write an equation for photosynthesis

Photosynthesis – Equation, Formula & Products

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In this tutorial, you will learn all about photosynthesis . We begin with an introduction to photosynthesis and its balanced chemical equation. Then, we analyze the two key stages involved in this process and take a look at the final products. Lastly, we consider the different types of photosynthesis.

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• Common Oxidizing Agents & Reducing Agents
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Introduction to Photosynthesis

The process by which plants and other organisms convert light energy (sunlight) into chemical energy (glucose) is known as photosynthesis. Sunlight powers a series of reactions that use water and carbon dioxide to synthesize glucose and release oxygen as a byproduct. Energy is stored in the chemical bonds of glucose and can be later harvested to fuel the organism’s activities through cellular respiration or fermentation .

Photosynthesis is an endergonic process because it requires an input of energy from the surroundings in order for a chemical change to take place. Furthermore, photosynthesis is a reduction-oxidation (redox) reaction , meaning that it involves the transfer of electrons between chemical species. During the process, carbon dioxide is reduced (i.e., gains electrons) to form glucose, and water is oxidized (i.e., loses electrons) to form molecular oxygen.

The complex process of photosynthesis takes place in chloroplasts (i.e., membrane-bound organelles in plant and algal cells). Chloroplasts have an outer membrane and an inner membrane. The stroma is the fluid-filled space within the inner membrane; it surrounds flattened sac-like structures known as thylakoids. Thylakoids consist of a thylakoid space (lumen) surrounded by a thylakoid membrane. The thylakoid membrane contains photosystems, which are large complexes of proteins and pigments. There are two types of photosystems: photosystem I (PSI) and photosystem II (PSII).

Chemical Equation for Photosynthesis

The overall balanced equation for photosynthesis is commonly written as 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 (shown below). In other words, six molecules of carbon dioxide and six molecules of water react in the presence of sunlight to produce one molecule of glucose (a six-carbon sugar) and six molecules of oxygen. 

Stages of Photosynthesis

There are two main stages of photosynthesis: the light-dependent reactions and the Calvin cycle.

Light-Dependent Reactions

The light-dependent reactions use light energy to make ATP (an energy-carrying molecule) and NADPH (an electron carrier) for use in the Calvin cycle. In addition, oxygen is released as a result of the oxidation of water. In plants and algae, the light-dependent reactions take place in the thylakoid membrane of chloroplasts. The most common form of the light-dependent reactions is a process known as non-cyclic photophosphorylation. This process involves two key steps: ATP synthesis (via photosystem II) and NADPH synthesis (via photosystem I).

• Step 1 (ATP Synthesis): Pigments in photosystem II (such as chlorophylls) absorb light and energize electrons. A proton gradient is formed as these excited electrons travel down an electron transport chain and release energy that pumps hydrogen ions from the stroma to the thylakoid lumen. The splitting of water molecules through photolysis produces hydrogen ions (as well as oxygen molecules) that further contribute to this electrochemical gradient. As hydrogen ions flow down their gradient (i.e., back across the thylakoid membrane and into the stroma), they travel through an enzyme known as ATP synthase. ATP synthase catalyzes the formation of adenosine triphosphate (ATP) using ADP (adenosine diphosphate) and inorganic phosphate (P i ).
• Step 2 (NADPH Synthesis): Electrons are transferred to photosystem I and energized by the light absorbed by PSI pigments. The electrons reach the end of the electron transport chain and are passed to an enzyme known as ferredoxin-NADP + reductase (FNR). FNR catalyzes the reaction by which NADP + is reduced to NADPH.

Calvin Cycle

The Calvin cycle (also referred to as the light-independent reactions) takes place in the stroma of chloroplasts and is not directly dependent on sunlight. Instead, this stage utilizes the products of the light-dependent reactions (ATP and NADPH), along with carbon dioxide, to synthesize glucose. The Calvin cycle consists of three basic steps: carbon fixation, reduction, and regeneration.

• Step 1 (Carbon Fixation): RuBisCO (the most abundant enzyme on Earth) catalyzes the carboxylation of ribulose-1,5-biphosphate (RuBP) by carbon dioxide to produce an unstable six-carbon compound. This six-carbon compound is then readily converted into two molecules of 3-phosphoglyceric acid (3-PGA).
• Step 2 (Reduction): An enzyme known as phosphoglycerate kinase catalyzes the phosphorylation of 3-PGA by ATP to produce 1,3-biphosphoglyceric acid (1,3-BPG) and ADP. Next, another enzyme (glyceraldehyde 3-phosphate dehydrogenase) catalyzes the reduction of 1,3-BPG by NADPH to produce glyceraldehyde 3-phosphate (G3P) and NADP + .
• Step 3 (Regeneration): Every turn of the Calvin cycle produces two molecules of G3P. Therefore, six turns of the cycle produce twelve molecules of G3P. Two of these G3P molecules exit the cycle and are used to synthesize one molecule of glucose. Meanwhile, the other ten molecules of G3P remain in the cycle and are used to regenerate six RuBP molecules. The regeneration of RuBP requires ATP, but it allows the cycle to continue.

Products of Photosynthesis

The major product of photosynthesis is glucose, a simple sugar with the molecular formula C 6 H 12 O 6 . Plants and other photosynthetic organisms use glucose for numerous functions, including those listed below.

• Cellular Respiration: Glucose is broken down in order to produce ATP (which can be used to fuel other cellular activities) through a process known as cellular respiration.
• Biosynthesis of Starch and Cellulose: Glucose molecules can be linked together to form complex carbohydrates such as starch and cellulose. Plants and other organisms use starch to store energy and cellulose to support/rigidify their cell walls.
• Protein Synthesis: Glucose can be combined with nitrates (from the soil) to produce amino acids, which can then be used to build proteins.

In addition, oxygen is released into the atmosphere during the process of photosynthesis. Plants (along with many other organisms) use oxygen to carry out aerobic respiration.

Types of Photosynthesis

There are three main types of photosynthesis: C3, C4, and CAM (crassulacean acid metabolism). They differ in the way that they manage photorespiration, a wasteful process that occurs when the enzyme rubisco acts on oxygen instead of carbon dioxide. Photorespiration competes with the Calvin cycle and decreases the efficiency of photosynthesis (by wasting energy and using up fixed carbon).

C3 Photosynthesis

The majority of plants use C3 photosynthesis, a process in which no special features or adaptations are used to combat photorespiration. Hot, dry climates are not ideal for C3 plants (e.g., rice, wheat, and barley) because of the increased rate of photorespiration, which is due to the buildup of oxygen that occurs when plants close their stomata (leaf pores) in order to prevent water loss.

C4 Photosynthesis

C4 photosynthesis reduces photorespiration by performing the initial carbon dioxide fixation and Calvin cycle in two different cell types. This process utilizes an additional enzyme known as phosphoenolpyruvate (PEP) carboxylase. PEP carboxylase does not react with oxygen (unlike rubisco) and is able to catalyze a reaction between carbon dioxide and PEP in the mesophyll cells to produce the intermediate four-carbon compound oxaloacetate. Oxaloacetate is then reduced to malate and transported to bundle sheath cells. In these cells, malate undergoes decarboxylation, forming a special compartment for the concentration of carbon dioxide around rubisco.

As a result, the Calvin cycle can proceed as normal, and an opportunity for rubisco to bind to oxygen is prevented. C4 plants (e.g., maize and sugarcane) have a competitive advantage over C3 plants in hot, dry environments where the benefits of reduced photorespiration outweigh the additional energy costs associated with C4 photosynthesis.

CAM Photosynthesis

Crassulacean acid metabolism, also known as CAM photosynthesis, reduces photorespiration by performing the initial carbon dioxide fixation and Calvin cycle at separate times. CAM plants (e.g., cactus and pineapple) open their stomata at night, allowing carbon dioxide to enter the leaf. The carbon dioxide is converted to oxaloacetate by PEP carboxylase, the same enzyme used in C4 photosynthesis. Oxaloacetate is subsequently reduced to malate, which is stored as malic acid in vacuoles .

During the day (when light is readily available), CAM plants close their stomata and prepare for the Calvin cycle. Malate is transported into chloroplasts and broken down to release carbon dioxide, which is heavily concentrated around the enzyme rubisco. Similar to C4 photosynthesis, crassulacean acid metabolism is an energetically expensive process. However, it is quite useful for plants in hot, arid climates that need to minimize photorespiration and conserve water.

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5.1: Overview of Photosynthesis

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All living organisms on earth consist of one or more cells. Each cell runs on the chemical energy found mainly in carbohydrate molecules (food), and the majority of these molecules are produced by one process: photosynthesis. Through photosynthesis, certain organisms convert solar energy (sunlight) into chemical energy, which is then used to build carbohydrate molecules. The energy used to hold these molecules together is released when an organism breaks down food. Cells then use this energy to perform work, such as cellular respiration .

The energy that is harnessed from photosynthesis enters the ecosystems of our planet continuously and is transferred from one organism to another. Therefore, directly or indirectly, the process of photosynthesis provides most of the energy required by living things on earth. Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe, humans depend almost entirely on the organisms that carry out photosynthesis.

CONCEPT IN ACTION

Click the following link to learn more about photosynthesis.

Solar Dependence and Food Production

Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. The Greek roots of the word autotroph mean “self” ( auto ) “feeder” ( troph ). Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae (Figure \(\PageIndex{1}\)). Oceanic algae contribute enormous quantities of food and oxygen to global food chains. Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight.

Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. The Greek roots of the word heterotroph mean “other” ( hetero ) “feeder” ( troph ), meaning that their food comes from other organisms. Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis. Humans are heterotrophs, as are all animals. Heterotrophs depend on autotrophs, either directly or indirectly. Deer and wolves are heterotrophs. A deer obtains energy by eating plants. A wolf eating a deer obtains energy that originally came from the plants eaten by that deer. The energy in the plant came from photosynthesis, and therefore it is the only autotroph in this example (Figure \(\PageIndex{2}\)). Using this reasoning, all food eaten by humans also links back to autotrophs that carry out photosynthesis.

BIOLOGY IN ACTION: Photosynthesis at the Grocery Store

Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle contains hundreds, if not thousands, of different products for customers to buy and consume (Figure \(\PageIndex{3}\)).

Although there is a large variety, each item links back to photosynthesis. Meats and dairy products link to photosynthesis because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from grains, which are the seeds of photosynthetic plants. What about desserts and drinks? All of these products contain sugar—the basic carbohydrate molecule produced directly from photosynthesis. The photosynthesis connection applies to every meal and every food a person consumes.

Main Structures and Summary of Photosynthesis

Photosynthesis requires sunlight, carbon dioxide, and water as starting reactants (Figure \(\PageIndex{4}\)). After the process is complete, photosynthesis releases oxygen and produces carbohydrate molecules, most commonly glucose. These sugar molecules contain the energy that living things need to survive.

The complex reactions of photosynthesis can be summarized by the chemical equation shown in Figure \(\PageIndex{5}\).

Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex, as in the way that the reaction summarizing cellular respiration represented many individual reactions. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the physical structures involved.

In plants, photosynthesis takes place primarily in leaves, which consist of many layers of cells and have differentiated top and bottom sides. The process of photosynthesis occurs not on the surface layers of the leaf, but rather in a middle layer called the mesophyll (Figure \(\PageIndex{6}\)). The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata.

In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. In plants, chloroplast-containing cells exist in the mesophyll. Chloroplasts have a double (inner and outer) membrane. Within the chloroplast is a third membrane that forms stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane are molecules of chlorophyll, a pigment (a molecule that absorbs light) through which the entire process of photosynthesis begins. Chlorophyll is responsible for the green color of plants. The thylakoid membrane encloses an internal space called the thylakoid space. Other types of pigments are also involved in photosynthesis, but chlorophyll is by far the most important. As shown in Figure \(\PageIndex{6}\), a stack of thylakoids is called a granum, and the space surrounding the granum is called stroma (not to be confused with stomata, the openings on the leaves).

ART CONNECTION

On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

The Two Parts of Photosynthesis

Photosynthesis takes place in two stages: the light-dependent reactions and the Calvin cycle. In the light-dependent reactions, which take place at the thylakoid membrane, chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water. The light-dependent reactions release oxygen from the hydrolysis of water as a byproduct. In the Calvin cycle, which takes place in the stroma, the chemical energy derived from the light-dependent reactions drives both the capture of carbon in carbon dioxide molecules and the subsequent assembly of sugar molecules. The two reactions use carrier molecules to transport the energy from one to the other. The carriers that move energy from the light-dependent reactions to the Calvin cycle reactions can be thought of as “full” because they bring energy. After the energy is released, the “empty” energy carriers return to the light-dependent reactions to obtain more energy.

The process of photosynthesis transformed life on earth. By harnessing energy from the sun, photosynthesis allowed living things to access enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy, allowing them to evolve new structures and achieve the biodiversity that is evident today.

Only certain organisms, called autotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that can absorb light and convert light energy into chemical energy. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules (usually glucose) and releases oxygen into the air. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place.

Art Connections

Figure \(\PageIndex{6}\): On a hot, dry day, plants close their stomata to conserve water. What impact will this have on photosynthesis?

Levels of carbon dioxide (a reactant) will fall, and levels of oxygen (a product) will rise. As a result, the rate of photosynthesis will slow down.

Contributors and Attributions

Samantha Fowler (Clayton State University), Rebecca Roush (Sandhills Community College), James Wise (Hampton University). Original content by OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-e119a8aafbdd ).

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General Education

The word photosynthesis comes from two Greek words: photo, meaning “light”, and synthesis, meaning “put together.” Looking at that those two roots, we have a good idea of what happens during the chemical process of photosynthesis: plants put together water and carbon dioxide with light to create glucose and oxygen.

In this article, we’ll break down what photosynthesis is, why photosynthesis is important, and discuss the chemical equation for photosynthesis: what it is and what each part of it means.

What Is Photosynthesis?

Put simply, photosynthesis is how plants, algae, and certain types of bacteria harness energy from sunlight to create chemical energy for themselves to live.

There are two main types of photosynthesis: oxygenic photosynthesis and anoxygenic photosynthesis. Oxygenic photosynthesis is more common—that’s the type we see in plants and algae. Anoxygenic photosynthesis mainly occurs in bacteria.

In oxygenic photosynthesis, plants use light energy to combine carbon dioxide (CO2) and water (H2O). This chemical reaction produces carbohydrates for the plants to consume and oxygen, which is released back into the air.

Anoxygenic photosynthesis is very similar, but it doesn’t produce oxygen. We’ll be focusing on the more common type of photosynthesis, oxygenic photosynthesis, for the rest of this article.

Why Is Photosynthesis Important?

Photosynthesis is important for a few reasons:

First, it produces energy that plants need to live. The resulting carbohydrates provide plants with the energy to grow and live.

Second, photosynthesis helps take in the carbon dioxide produced by breathing organisms and convert that into oxygen, which is then reintroduced back into the atmosphere. Basically, with photosynthesis, plants are helping produce the oxygen that all living things need to breathe and survive.

Photosynthesis Equation

Here is the chemical equation for photosynthesis:

6CO2 + 12H2O + Light Energy ------> C6H12O6 + 6O2 + 6H2O

Photosynthesis Formula Breakdown

Now that we know what the photosynthesis equation is, let’s break down each piece of the photosynthesis formula.

On the reactants side, we have:

6CO2 = Six molecules of carbon dioxide

12H2O = Twelve molecules of water

Light Energy = Light from the sun

On the products side, we have:

C6H12O6 = glucose

6O2 = six molecules of oxygen

6H2O = six molecules of water

As we learned earlier, the glucose will be used by the plant as energy. The oxygen and water will be released back into the atmosphere to help other living things.

What You Need to Know About the Photosynthesis Formula

During photosynthesis, plants use light energy to combine carbon dioxide and water to produce glucose, oxygen, and water.

Photosynthesis is important because it provides plants with the energy they need to survive. It also releases needed oxygen and water back into the atmosphere.

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Hayley Milliman is a former teacher turned writer who blogs about education, history, and technology. When she was a teacher, Hayley's students regularly scored in the 99th percentile thanks to her passion for making topics digestible and accessible. In addition to her work for PrepScholar, Hayley is the author of Museum Hack's Guide to History's Fiercest Females.

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The Photosynthesis Formula: Turning Sunlight into Energy

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Some organisms need to create the energy they need to survive. These organisms are capable of absorbing energy from sunlight and using it to produce sugar and other organic compounds such as lipids and proteins . The sugars are then used to provide energy for the organism. This process, called photosynthesis, is used by photosynthetic organisms including plants , algae , and cyanobacteria.

Photosynthesis Equation

In photosynthesis, solar energy is converted to chemical energy. The chemical energy is stored in the form of glucose (sugar). Carbon dioxide, water, and sunlight are used to produce glucose, oxygen, and water. The chemical equation for this process is:

6CO 2 + 12H 2 O + light → C 6 H 12 O 6 + 6O 2 + 6H 2 O

Six molecules of carbon dioxide (6CO 2 ) and twelve molecules of water (12H 2 O) are consumed in the process, while glucose (C 6 H 12 O 6 ), six molecules of oxygen (6O 2 ), and six molecules of water (6H 2 O) are produced.

This equation may be simplified as: 6CO 2 + 6H 2 O + light → C 6 H 12 O 6 + 6O 2 .

Photosynthesis in Plants

In plants, photosynthesis occurs mainly within the leaves . Since photosynthesis requires carbon dioxide, water, and sunlight, all of these substances must be obtained by or transported to the leaves. Carbon dioxide is obtained through tiny pores in plant leaves called stomata. Oxygen is also released through the stomata. Water is obtained by the plant through the roots and delivered to the leaves through vascular plant tissue systems . Sunlight is absorbed by chlorophyll, a green pigment located in plant cell structures called chloroplasts . Chloroplasts are the sites of photosynthesis. Chloroplasts contain several structures, each having specific functions:

• Outer and inner membranes — protective coverings that keep chloroplast structures enclosed.
• Stroma —dense fluid within the chloroplast. The site of conversion of carbon dioxide to sugar.
• Thylakoid —flattened sac-like membrane structures. The site of conversion of light energy to chemical energy.
• Grana —densely layered stacks of thylakoid sacs. Sites of conversion of light energy to chemical energy.
• Chlorophyll —a green pigment within the chloroplast. Absorbs light energy.

Stages of Photosynthesis

Photosynthesis occurs in two stages. These stages are called the light reactions and the dark reactions. The light reactions take place in the presence of light. The dark reactions do not require direct light, however dark reactions in most plants occur during the day.

Light reactions occur mostly in the thylakoid stacks of the grana. Here, sunlight is converted to chemical energy in the form of ATP (free energy containing molecule) and NADPH (high energy electron carrying molecule). Chlorophyll absorbs light energy and starts a chain of steps that result in the production of ATP, NADPH, and oxygen (through the splitting of water). Oxygen is released through the stomata. Both ATP and NADPH are used in the dark reactions to produce sugar.

Dark reactions occur in the stroma. Carbon dioxide is converted to sugar using ATP and NADPH. This process is known as carbon fixation or the Calvin cycle. The Calvin cycle has three main stages: carbon fixation, reduction, and regeneration. In carbon fixation, carbon dioxide is combined with a 5-carbon sugar [ribulose1,5-biphosphate (RuBP)] creating a 6-carbon sugar. In the reduction stage, ATP and NADPH produced in the light reaction stage are used to convert the 6-carbon sugar into two molecules of a 3-carbon carbohydrate , glyceraldehyde 3-phosphate. Glyceraldehyde 3-phosphate is used to make glucose and fructose. These two molecules (glucose and fructose) combine to make sucrose or sugar. In the regeneration stage, some molecules of glyceraldehyde 3-phosphate are combined with ATP and are converted back into the 5-carbon sugar RuBP. With the cycle complete, RuBP is available to be combined with carbon dioxide to begin the cycle over again.

Photosynthesis Summary

In summary, photosynthesis is a process in which light energy is converted to chemical energy and used to produce organic compounds. In plants, photosynthesis typically occurs within the chloroplasts located in plant leaves. Photosynthesis consists of two stages, the light reactions, and the dark reactions. The light reactions convert light into energy (ATP and NADHP) and the dark reactions use the energy and carbon dioxide to produce sugar. For a review of photosynthesis, take the Photosynthesis Quiz .  

• Photosynthesis Basics - Study Guide
• Chloroplast Function in Photosynthesis
• Photosynthesis Vocabulary Terms and Definitions
• What Are the Products of Photosynthesis?
• Calvin Cycle Steps and Diagram
• 10 Fascinating Photosynthesis Facts
• What Is the Primary Function of the Calvin Cycle?
• All About Photosynthetic Organisms
• Chlorophyll Definition and Role in Photosynthesis
• Examples of Chemical Reactions in Everyday Life
• Thylakoid Definition and Function
• The Balanced Chemical Equation for Photosynthesis
• Laws of Thermodynamics as Related to Biology
• Adaptations to Climate Change in C3, C4, and CAM Plants
• All About Cellular Respiration

Biology Notes Online

Photosynthesis – Definition, Steps, Equation, Process, Diagram, Examples

Table of Contents

What is Photosynthesis?

• Photosynthesis is a fundamental biochemical process that harnesses the energy of light to synthesize glucose molecules. This intricate mechanism can be delineated into two primary stages. Initially, light energy is captured and transformed into chemical energy, stored within the molecules of adenosine triphosphate ( ATP ) and nicotinamide adenine dinucleotide phosphate (NADPH).
• Subsequently, these energy-rich cofactors participate in the Calvin Cycle, a series of reactions that facilitate the synthesis of organic molecules by assimilating carbon atoms from carbon dioxide (CO2). These organic molecules can either be utilized by mitochondria to generate ATP or amalgamated to yield glucose, sucrose, and other carbohydrates.
• Scientifically defined, photosynthesis is a cellular process employed by a myriad of organisms to transmute light energy into chemical energy. This stored chemical energy is embedded within organic compounds, which, upon metabolism via cellular respiration, release energy essential for the organism’s functions.
• Predominantly, the term “photosynthesis” alludes to oxygenic photosynthesis, characterized by the production of oxygen as a byproduct and the storage of some resultant chemical energy within carbohydrate molecules, including sugars, starch, and cellulose .
• This form of photosynthesis is executed by a majority of plants, algae, and cyanobacteria, collectively termed as photoautotrophs. Notably, photosynthesis plays a pivotal role in sustaining Earth’s atmospheric oxygen levels and furnishing the majority of biological energy requisite for Earth’s complex life forms.
• However, certain bacteria undergo anoxygenic photosynthesis, utilizing bacteriochlorophyll to cleave hydrogen sulfide, leading to the production of sulfur instead of oxygen. Furthermore, specific Archaea , such as Halobacterium, engage in a distinct form of non-carbon-fixing anoxygenic photosynthesis, leveraging simpler photopigments like retinal to absorb light and directly synthesize ATP . This archaic form of photosynthesis is postulated to be one of the earliest evolutionary adaptations on Earth.
• Regardless of the organism or method, photosynthesis invariably commences with the absorption of light energy by proteins known as reaction centers, which contain photosynthetic pigments or chromophores. In plants, these proteins, predominantly chlorophyll, are housed within organelles termed chloroplasts. During the light-dependent reactions, electrons are extracted from substances like water, resulting in the release of oxygen gas. The liberated hydrogen aids in the formation of NADPH and ATP .
• In plants, algae, and cyanobacteria, the Calvin cycle subsequently facilitates the synthesis of sugars. Here, atmospheric carbon dioxide is integrated into pre-existing organic carbon compounds, utilizing the ATP and NADPH generated earlier. In certain bacteria, alternative mechanisms achieve carbohydrate synthesis.
• Historically, the earliest photosynthetic organisms likely utilized reducing agents such as hydrogen or hydrogen sulfide. The advent of cyanobacteria marked a significant evolutionary milestone, as the surplus oxygen they generated significantly influenced Earth’s atmospheric composition, paving the way for the evolution of complex life forms.
• Presently, photosynthesis captures energy at an astounding rate of approximately 130 terawatts, surpassing the current global power consumption. Furthermore, photosynthetic organisms assimilate between 100–115 billion tons of carbon annually.
• In conclusion, photosynthesis is not only a cornerstone of life on Earth but also plays a crucial role in global climate processes by sequestering carbon dioxide. This intricate process, first identified by Jan Ingenhousz in 1779, remains a testament to nature’s ingenuity and efficiency.

Definition of Photosynthesis

Photosynthesis is the biological process by which plants, algae, and certain bacteria convert light energy into chemical energy, producing oxygen and organic compounds, primarily glucose, from carbon dioxide and water.

Experimental History

The intricate process of photosynthesis, which underpins life on Earth, has been the subject of extensive scientific inquiry over the centuries. This journey of discovery, refinement, and development has been marked by the contributions of numerous scientists, each building upon the work of their predecessors. Below is a summarized account of the experimental history of photosynthesis:

Where Does Photosynthesis take place?

Photosynthesis primarily occurs in the chloroplasts, specialized organelles found predominantly in plant leaves. These chloroplasts belong to a category of organelles known as plastids, which are membrane-bound structures responsible for various vital cellular functions.

• Chloroplast Structure : Chloroplasts are a type of primary plastid characterized by a double-membrane structure. They house the essential green pigment, chlorophyll, which plays a pivotal role in capturing light energy. In contrast, secondary plastids, found in certain plankton species, possess multiple membranes.
• Role of Chlorophyll : Chlorophyll pigments are responsible for absorbing light energy from the sun. Upon absorption, a chlorophyll molecule releases an electron, initiating the process of converting light energy into chemical energy.
• Reaction Centers : These are specialized complexes composed of pigments and proteins. They serve as the primary sites where light energy is transformed into chemical energy, marking the onset of electron transfer. The energy captured by the reaction centers is crucial for driving the subsequent biochemical reactions of photosynthesis.

In summary, photosynthesis is a complex process that takes place within the chloroplasts of plant cells. The chlorophyll pigments housed within these organelles are instrumental in capturing and converting light energy into a form that can be utilized by the plant for growth and sustenance.

Photosynthesis: a two-stage process

Photosynthesis, a fundamental biochemical process, can be delineated into two distinct stages. Contrary to the traditional classification of these stages as ‘light’ and ‘dark’ reactions, contemporary scientific understanding emphasizes that both stages are influenced by light, albeit in different capacities.

1. Photochemical Reaction Process (Light-Dependent Reactions):

In this initial stage, light energy, primarily from the sun, is harnessed and converted into chemical energy in the form of adenosine triphosphate ( ATP ). This process, known as photophosphorylation, is contingent upon the presence of light. During this phase:

• Photons are absorbed by photosynthetic pigments, initiating a series of electron transfer events.
• The energy derived from these events drives the synthesis of ATP and the electron carrier molecule, nicotinamide adenine dinucleotide phosphate (NADPH).
• Oxygen is released as a byproduct when water molecules are split.

2. Carbon Fixation Process (Light-Independent Reactions):

While this stage does not directly utilize light energy, it is influenced by the products of the light-dependent reactions. The primary objective here is the conversion of inorganic carbon into organic compounds. This energy-consuming, endergonic process can manifest in two distinct pathways:

• Carbon dioxide from the atmosphere is captured and integrated into existing organic molecules.
• The ATP and NADPH produced in the light-dependent reactions provide the energy and electrons, respectively, for the synthesis of glucose and other carbohydrates.
• Non-Calvin Cycle: This alternative pathway is exclusive to certain anoxygenic photosynthetic organisms. It diverges from the Calvin cycle in its mechanism of carbon fixation and the compounds produced.

In summation, photosynthesis is a two-stage process wherein light energy is first converted into chemical energy, which subsequently powers the synthesis of organic compounds from inorganic carbon. Both stages, while functionally distinct, are interdependent and collectively contribute to the sustenance of life on Earth.

Photosynthesis equations/reactions/formula

Photosynthesis, a fundamental biochemical process, varies between green plants and sulfur bacteria in terms of the reactants used and the products formed.

Oxygenic Photosynthesis in Plants:

In green plants, photosynthesis utilizes water and carbon dioxide, harnessing solar energy to produce glucose and oxygen. The overarching equation representing this process is:

6 CO 2 ​+6 H 2​ O +light energy→ C 6 ​ H 12 ​ O 6 ​+6 O 2​

Alternatively, it can be represented as:

6 CO 2 ​+12 H 2 ​ O +light energy→ C 6 ​ H 12 ​ O 6 ​+6 O 2​ +6 H 2 ​ O

This equation signifies that six molecules of carbon dioxide and twelve molecules of water, in the presence of light energy, yield one molecule of glucose, six molecules of oxygen, and six molecules of water. It’s noteworthy that while a triose (3-carbon molecule) is the direct product of photosynthesis, glucose, a hexose, is often depicted as the end product due to its foundational role in cellular processes. Additionally, the oxygen produced serves dual purposes: it is utilized by the plant during oxidative phosphorylation and is also released into the atmosphere, facilitating aerobic respiration in other organisms.

Anoxygenic Photosynthesis in Sulfur Bacteria:

Sulfur bacteria employ a distinct form of photosynthesis. Instead of water, they use hydrogen sulfide in conjunction with carbon dioxide. The general equation for this process is:

CO 2 ​+2 H 2 ​ S +light energy→( CH 2 ​ O )+ H 2 ​ O +2 S

This equation illustrates that carbon dioxide and hydrogen sulfide, under the influence of light energy, produce carbohydrates, water, and elemental sulfur.

In summation, photosynthesis, whether in plants or sulfur bacteria, is a series of intricate reactions that convert simple molecules into energy-rich compounds, using light as the primary energy source. The specific reactants and products differ based on the organism, but the core principle of harnessing light energy remains consistent.

Types of Photosynthesis

Photosynthesis, the fundamental process by which organisms convert light energy into chemical energy, manifests in various forms across different species. These diverse pathways are tailored to the specific environmental conditions and metabolic needs of the organisms. Here, we delve into the primary types of photosynthesis and their distinctive characteristics.

• Organisms : Predominantly found in cereals like wheat and rice, as well as in cotton, potatoes, and soybeans.
• Process : The enzyme Rubisco facilitates the fixation of CO2, producing a three-carbon molecule, 3-phosphoglyceric acid (3-PGA).
• Organisms : Plants such as sugarcane and maize.
• Process : CO2 is initially fixed into a four-carbon compound, oxaloacetate, which is subsequently converted to malate. This malate is transported to the bundle sheath cells, where it releases CO2. This CO2 is then utilized in the Calvin cycle, akin to the C3 pathway. Notably, C4 plants exhibit enhanced water-use efficiency in hot, arid conditions.
• Organisms : Adapted to extremely arid environments, plants like cacti and pineapples employ this pathway.
• Process : To mitigate water loss, these plants open their stomata during the cooler nighttime hours, absorbing CO2. This CO2 is fixed into organic acids, which are stored until daylight, when they are utilized in the light-dependent reactions of photosynthesis.
• Prokaryotic Photosynthesis : Executed by organisms without a defined nucleus, such as certain bacteria.
• Eukaryotic Photosynthesis : Conducted by organisms with a well-defined nucleus, including protists and green plants.
• Organisms : Cyanobacteria (prokaryotic) and protists like diatoms, dinoflagellates, and Euglena (eukaryotic). Additionally, green plants, spanning from algae to angiosperms, employ this pathway.
• Characteristic : Oxygen is evolved as a byproduct.
• Organisms : Exclusively prokaryotic, including green sulfur bacteria and purple bacteria.
• Characteristic : Oxygen is not released during the process.

In summary, photosynthesis, though universally critical for life on Earth, manifests in a myriad of forms, each tailored to the unique needs and environments of the photosynthesizing organisms.

Photosynthetic pigments

Photosynthetic pigments are specialized molecules that absorb and harness light energy, facilitating the conversion of this energy into chemical energy during the process of photosynthesis. These pigments are pivotal for the efficient absorption of light across various wavelengths.

1. Chlorophyll: Chlorophyll, predominantly green in color, is the primary pigment responsible for capturing light energy. Its salient features include:

• Nature: It is a lipid-based molecule.
• Location: Predominantly found within the thylakoid membranes of chloroplasts.
• Types: Several variants exist, including chlorophyll-a, b, c, and d. Among these, chlorophyll-a is the primary photosynthetic pigment.
• Structure: Chlorophyll-a, b, and d are derivatives of “chlorin,” while chlorophyll-c is a “porphyrin” derivative. A unique feature is the presence of a central magnesium ion (Mg^2+).
• Function: Chlorophyll is instrumental in capturing and storing solar energy, and it plays a pivotal role in the photochemical reactions of photosynthesis.

2. Carotenoids: Carotenoids, often yellow, red, or purple, work synergistically with chlorophyll. Their key characteristics are:

• Nature: These are lipid-soluble molecules.
• Types: Over 150 variants of carotenoids have been identified.
• Forms: They exist as simple hydrocarbons (e.g., beta-carotene) or oxygenated hydrocarbons (e.g., lutein).
• Function: Carotenoids assist in energy transfer, act as free-radical scavengers, and provide photoprotection by quenching excess energy.

3. Phycobilins: Distinct from chlorophyll and carotenoids, phycobilins are present in specific oxygenic photosynthetic organisms, particularly cyanobacteria and red algae.

• Types: Notable variants include Phycoerythrobilin, Phycocyanobilins, and Allophycocyanobilins.
• Structure: These pigments possess a tetrapyrrole structure and do not require magnesium ions.
• Location: Being water-soluble, phycobilins, in conjunction with proteins, form phycobiliproteins. These proteins aggregate into clusters known as phycobilisomes, which adhere to membranes.
• Function: Phycobilins are primarily involved in resonance energy transfer.

4. Bacteriorhodopsin: Exclusive to halobacteria, bacteriorhodopsin is a pigment that consists of a protein linked to a retinal prosthetic group. It plays a role in light absorption, leading to proton expulsion from the cell.

In summary, photosynthetic pigments are integral to the process of photosynthesis, ensuring efficient light absorption and energy conversion. Each pigment type has a distinct role and absorption spectrum, collectively ensuring that a broad range of light wavelengths is harnessed for photosynthesis.

Structure Of Chlorophyll

Chlorophyll, the quintessential green pigment in plants, possesses a unique molecular structure that facilitates its primary function: the absorption of sunlight for photosynthesis.

• Central Composition : At the core of chlorophyll’s structure lies a magnesium atom, encircled by four nitrogen atoms. This configuration is pivotal for its light-absorbing properties.
• Hydrocarbon Tail : Attached to this core is a hydrocarbon tail, which anchors the molecule to the thylakoid membrane within the chloroplasts.
• Chlorophyll-b : This assists chlorophyll-a in capturing light energy and is found alongside it in many plants.
• Chlorophyll-c1 and c2 : Typically found in certain algae species.
• Chlorophyll-d : Present in some cyanobacteria, it absorbs energy from different wavelengths of light compared to chlorophyll-a.
• Chlorophyll-f : Unique for its ability to absorb near-infrared light, making it more efficient than chlorophyll-a in certain conditions.
• Distribution : While green plants predominantly contain chlorophyll-a and chlorophyll-b, other photosynthesizing organisms, like certain algae and cyanobacteria, have the other variants, allowing them to optimize light absorption in diverse environments.

In essence, the structure of chlorophyll, with its central magnesium atom and various molecular variants, is ingeniously designed to maximize the absorption of sunlight, driving the life-sustaining process of photosynthesis across diverse organisms.

Factors affecting photosynthesis

Photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy, is influenced by a myriad of both external and internal factors. A comprehensive understanding of these factors is pivotal for optimizing the photosynthetic efficiency of plants.

1. Light Intensity, Quality, and Duration:

• Sciophytes: Flourish under diffused light conditions. (e.g., Oxalis)
• Heliophytes: Thrive under direct sunlight. (e.g., Dalbergia)
• Quality: Photosynthetically Active Radiation (PAR) denotes the fraction of light that actively participates in photosynthesis, typically ranging between 400-700nm in wavelength.
• Duration: While the duration of light exposure doesn’t directly alter the rate of photosynthesis, it does influence the total photosynthetic output.

2. Temperature:

Temperature plays a pivotal role in enzymatic activities associated with photosynthesis. For C3 plants, the optimal temperature range lies between 20-25°C, while C4 plants exhibit peak efficiency between 30-45°C. Beyond these ranges, enzymatic activities can diminish, potentially hampering the photosynthetic rate.

3. Carbon Dioxide Concentration:

Carbon dioxide (CO2) is a primary substrate in the photosynthetic process. An increase in its concentration can enhance the photosynthetic rate in C3 plants. However, C4 plants, equipped with a CO2 enrichment mechanism, exhibit a plateau in their photosynthetic rate even with elevated CO2 levels. The CO2 Compensation Point represents a threshold where the illuminated plant part ceases to absorb CO2.

4. Water Availability:

Water is indispensable for photosynthesis, participating in both light-dependent and light-independent reactions. A deficiency can impede the electron flow in Photosystem II and disrupt the Calvin cycle, thereby affecting the overall photosynthetic efficiency.

5. Genetic Factors:

Intrinsic genetic factors can also influence photosynthesis. Variations in genes encoding for photosynthetic machinery can lead to differences in their efficiency and functionality. Some species have evolved unique mechanisms to enhance photosynthetic efficiency, adapting to their specific environmental conditions.

In conclusion, photosynthesis is a multifaceted process influenced by a confluence of environmental and genetic factors. Understanding these factors and their interplay can provide insights into optimizing photosynthetic efficiency, with potential implications for agriculture and bioenergy production.

Photosynthetic Membranes and Organelles

Photosynthesis, the fundamental process by which energy from sunlight is converted into chemical energy, is facilitated by specific pigment molecules that absorb photons of light. The efficiency of this process is contingent upon the absorption of light within a precise wavelength range, ensuring the optimal energy required for photosynthesis.

To achieve this specificity in light absorption, phototrophic organisms have evolved specialized structures known as reaction center proteins. These proteins house the pigment molecules and are strategically positioned within the membranes of the organisms to optimize light absorption.

• In prokaryotes, the photosynthetic machinery is embedded directly within the cell or thylakoid membranes present in the cytosol.
• Unlike eukaryotes, prokaryotes lack specialized organelles like chloroplasts. Instead, their photosystems are integrated within the cellular architecture, ensuring efficient light capture and energy conversion.
• Eukaryotic organisms, such as green plants, possess specialized organelles known as chloroplasts. These chloroplasts are the hubs of photosynthetic activity.
• Within the chloroplasts, the thylakoid membranes house the photosystems. These membranes are laden with chlorophyll and other pigments, facilitating the absorption of light and the subsequent conversion of this energy into chemical forms.

In essence, the spatial organization of pigment molecules within specific membranes and organelles is a testament to the evolutionary adaptations of organisms to harness light energy efficiently. This intricate arrangement ensures that photosynthesis proceeds optimally, sustaining life on Earth.

Organelle for Photosynthesis

• The chloroplast is a pivotal organelle in eukaryotic cells, serving as the primary site for photosynthesis. Eukaryotic organisms, which encompass a diverse range of life forms, rely on chloroplasts to harness light energy and convert it into chemical energy.
• A typical plant cell is endowed with approximately 10 to 100 chloroplasts, underscoring their significance in the photosynthetic process. Delving deeper into the structure of the chloroplast, one encounters the thylakoids. These are specialized, membrane-bound compartments housed within the chloroplast.
• The thylakoid is not exclusive to eukaryotic chloroplasts; it is also found in the cytosol of cyanobacteria. However, it’s worth noting that while cyanobacteria possess thylakoids, they lack chloroplasts as a distinct organelle. The thylakoid is instrumental in the initial stages of photosynthesis, specifically the light-dependent or photochemical reactions.
• This compartment is intricately structured, comprising the membrane, lumen, and lamellae. Embedded within the thylakoid membranes are chlorophyll molecules, the green pigments responsible for capturing light energy.
• These molecules play a central role in the absorption and conversion of light energy, initiating the cascade of reactions that culminate in the synthesis of organic molecules. In summary, the chloroplast, with its resident thylakoids, stands as the cornerstone of photosynthesis in eukaryotic organisms, orchestrating the intricate processes that transform light into life-sustaining energy.

Process/ Steps of Photosynthesis – Mechanisms of Photosynthesis

Photosynthesis, a cornerstone of plant physiology, is a systematic process that facilitates the conversion of light energy into chemical energy stored in organic molecules. This intricate mechanism can be elucidated through the following sequential stages:

• Light Absorption: Within the chloroplasts, thylakoid membranes house chlorophyll molecules and other pigments. These molecules are adept at capturing light energy. Once absorbed, this energy facilitates the extraction of electrons from a donor, typically water. This electron removal results in the formation of oxygen. The primary electron acceptor in this phase is quinine (Q), akin to CoQ present in the electron transport chain.
• Electron Transport: Post the initial absorption, the electrons are relayed from the primary electron acceptor to a series of molecular intermediaries located within the thylakoid membrane. The culmination of this transfer sees the electrons being accepted by NADP+, the terminal electron acceptor. Concurrently, as electrons traverse the membrane, protons are actively extricated, engendering a proton gradient across the membrane.
• ATP Synthesis: Leveraging the established proton gradient, protons traverse from the thylakoid lumen back to the stroma via the F0F1 complex. This movement is instrumental in the phosphorylation of ADP, resulting in the generation of ATP . This phase mirrors the ATP synthesis observed in the mitochondrial electron transport chain.
• Carbon Reduction: With the energy and electrons furnished by NADP and ATP from the preceding steps, carbon dioxide undergoes a reduction process, culminating in the formation of six-carbon sugar molecules. It’s imperative to note that while the initial three stages are contingent on light, rendering them “light reactions”, the carbon reduction step operates independently of light, earning it the designation of “dark reactions”.

In summation, photosynthesis is a meticulously orchestrated sequence of events, harmonizing light-dependent and light-independent reactions to produce organic compounds vital for plant sustenance and growth.

Types/ Stages/ Parts of photosynthesis

Photosynthesis can be split into two stages that are based on the use of light energy

1. Light-dependent reactions

Photosynthesis, a pivotal biochemical process, encompasses a series of reactions that convert light energy into chemical energy. The light-dependent reactions, as the name suggests, are contingent on the presence of light and primarily transpire within the thylakoid membranes of chloroplasts. These reactions can be systematically delineated into the following stages:

1. Photon Absorption and Light Harvesting

The initial phase involves the capture of photons by chlorophyll molecules, accessory pigments, and associated proteins, collectively termed photoreceptors. These photoreceptors are organized into intricate assemblies, comprising a photosynthetic reaction center, core antenna complexes, and light-harvesting complexes (LHC). The core antenna and LHC, constituted by accessory pigments and chlorophyll-bound proteins, function as photon traps, capturing diverse wavelengths of light. Sequentially, the absorbed photon energy is channeled towards the photosynthetic reaction center.

Two distinct photosynthetic reaction centers are present in plants, green algae, and cyanobacteria:

• Photosystem I (PSI): Primarily utilizing chlorophyll a, PSI is excited by light with a peak wavelength of 700 nanometers (P700).
• Photosystem II (PSII): Incorporating both chlorophyll a and b, PSII can absorb light up to a wavelength of 680 nanometers (P680).

2. Electron Transport Dynamics:

Photon absorption culminates in the elevation of an electron to a heightened energy state, engendering a negatively charged radical. This unstable state prompts the electron’s spontaneous transfer to a proximate acceptor molecule, rendering the photoreceptor positively charged. Subsequent replenishment of the photoreceptor is achieved through electrons derived either from water or another electron transfer chain.

Electron transfer ensues through a series of complexes:

• PSI (Plastocyanin-Ferredoxin Oxidoreductase): Here, the excited electron from P700 is relayed to plastocyanin (PC), which subsequently donates the electron to ferredoxin (Fd). Concurrently, NADP+ is reduced to NADPH in the stroma.
• PSII: The excited P680 electron is sequentially transferred to pheophytin and plastoquinone. The resultant plastoquinol diffuses to the Cytochrome b6f complex. The oxygen-evolving complex (OEC) facilitates the replenishment of P680 by catalyzing water oxidation, releasing oxygen and protons.
• Cytochrome b6f Complex: Serving as a bridge between the photosystems, this complex facilitates linear electron flow, adhering to the Z scheme. The electron transfer is concomitant with proton translocation, engendering a proton gradient vital for ATP synthesis.

3. Photophosphorylation:

Two pathways exist for ATP synthesis:

• Z Scheme Pathway (Non-Cyclic Photophosphorylation): The proton gradient established during electron transfer drives ATP synthesis via ATP-H+ synthase, converting ADP to ATP .
• Cyclic Photophosphorylation: Here, electron flow is circumscribed between PSI and the Cytochrome b6f complex. The resultant proton gradient similarly facilitates ATP synthesis.

In essence, light-dependent reactions are a harmonious interplay of photon absorption, electron transport, and ATP synthesis, laying the foundation for the subsequent light-independent reactions of photosynthesis.

Wavelengths of light involved and their absorption

Light, a fundamental driver of photosynthesis, is composed of a spectrum of wavelengths, each with its distinct properties. The entirety of this spectrum, spanning from 390 to 760 nanometers (nm), constitutes the visible light spectrum perceivable by the human eye. However, not all these wavelengths are equivalently harnessed by photosynthetic organisms.

Within the broad spectrum of visible light lies a critical subset termed PAR, or Photosynthetically Active Radiation. This segment, ranging from 400 to 760 nm, is of paramount importance to photosynthetic processes. Within PAR, specific wavelengths play distinct roles:

• Blue Light (470-500 nm): This segment of the spectrum is actively absorbed and utilized by photosynthetic organisms. It plays a pivotal role in phototropic responses and chlorophyll production, thereby influencing plant growth and development.
• Red Light (660-760 nm): Another crucial segment for photosynthesis, red light is absorbed efficiently by chlorophyll pigments, driving the photosynthetic process.
• Green Light (500-580 nm): Contrary to the active absorption of blue and red lights, green light is predominantly reflected by plants. This reflection imparts the characteristic green hue to most plants. It’s worth noting that while the green light is majorly reflected, it is not entirely unused; a fraction is absorbed, albeit less efficiently than blue or red light.
• Blue-Green Light: While the spectrum does encompass blue-green wavelengths, it is the blue light, not the blue-green, that is harnessed for photosynthesis.

In summation, while the visible spectrum is vast, photosynthetic organisms exhibit selectivity in the wavelengths they absorb and utilize. This selective absorption and reflection not only drive the photosynthetic process but also influence the very appearance of plants in our environment.

Absorption spectrum and action spectrum

In the realm of photosynthesis, understanding the interaction between light and pigments is paramount. Two critical spectra, the absorption spectrum and the action spectrum, provide insights into this interaction. These spectra elucidate the efficiency of different wavelengths in the photosynthetic process and the role of specific pigments.

• Definition: The absorption spectrum is a graphical representation that delineates the efficiency with which a specific pigment absorbs various wavelengths of light.
• Graphical Representation: On the X-axis, the graph plots the wavelengths of light (measured in nanometers/nm), while the Y-axis represents the percentage of light absorption by the pigment.
• Characteristics: Each pigment possesses a unique absorption spectrum, making it a signature representation of that pigment. For instance, chlorophyll-a and chlorophyll-b have distinct absorption peaks, indicating their preferential absorption of specific wavelengths.
• Example: Chlorophyll-a predominantly absorbs light at 430 nm (blue) and 660 nm (red), with a higher absorption efficiency at 660 nm. In contrast, chlorophyll-b exhibits optimal absorption at 430 nm (blue) and 660 nm (red), with a pronounced peak at 430 nm.
• Definition: The action spectrum offers a depiction of the effectiveness of different light wavelengths in instigating the photosynthetic process.
• Graphical Representation: The X-axis plots the wavelengths of light (in nanometers/nm), while the Y-axis showcases the rate of photosynthesis, typically quantified by the amount of oxygen released.
• Interrelation with Absorption Spectrum: Overlaying the action spectrum with the absorption spectrum of a pigment can elucidate the contribution of specific wavelengths to photosynthetic efficiency and productivity.
• Significance: While the absorption spectrum can be determined for any photosynthetic pigment, the action spectrum is specifically associated with the primary photochemical reaction-performing pigment, chlorophyll-a. This pigment is located at the reaction center, where the evolution of oxygen gas, indicative of photosynthetic activity, predominantly occurs. Given its direct link to the excitation of the chlorophyll-a molecule, the action spectrum is exclusively attributed to this pigment.

In summary, while the absorption spectrum provides insights into the light-absorbing capabilities of pigments, the action spectrum reveals the functional efficacy of these absorbed wavelengths in driving photosynthesis. Together, these spectra offer a comprehensive understanding of the intricate interplay between light and photosynthetic pigments.

What actually happens in the Light-dependent reaction

The light-dependent reaction is a pivotal phase in photosynthesis, transpiring within the chloroplasts. This process is initiated by the absorption of light energy and culminates in the synthesis of ATP and NADPH, which are quintessential for the subsequent light-independent reactions. Here’s a detailed elucidation of the events that transpire during the light-dependent reaction:

• Upon the absorption of a photon by a chlorophyll molecule, specifically P680, the molecule becomes photoexcited and releases an electron.
• This event marks the commencement of the photochemical electron flow.
• The excited electron is initially relayed to the D1/D2 protein complex.
• Subsequently, it is transferred to a modified chlorophyll variant and then to “pheophytin.”
• The electron journey continues as it moves to plastoquinone A and eventually to plastoquinone B.
• The orchestrated electron flow sets in motion an electron transport chain, which plays a pivotal role in the light-dependent reactions.
• One of the primary outcomes of this electron flow is the reduction of NADP to NADPH. This molecule, NADPH, is instrumental in the subsequent light-independent reactions of photosynthesis.
• Concurrently, the electron flow engenders a proton gradient across the chloroplast membrane.
• The established proton gradient is harnessed by the ATP synthase enzyme.
• Utilizing this gradient, ATP synthase facilitates the phosphorylation of ADP to generate ATP .
• The synthesized ATP serves as an energy reservoir for the ensuing light-independent reactions.

In essence, the light-dependent reaction is a meticulously orchestrated sequence of events that harnesses light energy to produce ATP and NADPH. These molecules are indispensable for the sustenance of the photosynthetic process and the plant’s overall energy requirements.

Water photolysis

Water photolysis, also known as the oxygen-evolving process, is a fundamental mechanism within the photosynthetic pathway. This process is responsible for replenishing the electron deficit experienced by the chlorophyll molecule during the initial stages of photosynthesis. Here’s a comprehensive overview of water photolysis:

• During photosynthesis, the chlorophyll molecule loses an electron upon photon absorption. To sustain the continuity of the photosynthetic electron transport chain, this electron deficit must be addressed.
• The mechanism that compensates for this electron loss is the photolysis of water molecules, facilitated by the “oxygen-evolving complex” situated in the thylakoid membrane.
• As a consequence of water photolysis, oxygen is evolved. This process not only replenishes the lost electron to the chlorophyll molecule but also results in the liberation of oxygen gas, a byproduct of photosynthesis.
• The origin of the oxygen released during photosynthesis was a subject of scientific debate. Initial hypotheses posited that the oxygen atom from CO2 might be the source of the evolved oxygen.
• However, through collaborative research, the mystery was unraveled. C.B. Van Niel, studying purple photosynthetic bacteria, provided indirect evidence suggesting that the oxygen source was water molecules, not CO2.
• This assertion was further corroborated by Ruben, Hassid, and Kamen, who employed isotopic studies to furnish direct evidence that the oxygen evolved during photosynthesis indeed originates from H2O molecules.
• The photolysis process involves the hydrolysis of two water molecules, culminating in the release of one molecule of oxygen gas. This can be represented by the following equation for the light-dependent reactions: 2 H 2​ O +2 N A D P ++3 A D P +3 P i + l i g h t →2 N A D P H +2 H ++3 A TP + O 2​

In essence, water photolysis is a pivotal process in photosynthesis, ensuring the continuity of the electron transport chain and facilitating the release of oxygen, which is vital for aerobic life forms on Earth.

In the realm of photosynthesis, the photochemical reactions can be categorized into two primary types: cyclic and non-cyclic reactions. These reactions are distinguished by the involvement and flow of electrons through photosystems.

• This reaction involves solely Photosystem I (PS1).
• Upon photon absorption, the P700 chlorophyll molecule in PS1 becomes excited. The excited electron then traverses a sequence of molecules: from Fe-S to Ferredoxin, followed by Plastoquinone, the Cytochrome b6f complex, and finally to Plastocyanin.
• Given the exclusive involvement of PS1, the electron flow forms a loop, rendering it cyclic. This process culminates in what is termed cyclic phosphorylation.
• This reaction predominantly occurs in the stroma lamellae, especially when light with a wavelength exceeding 680nm is available.
• This reaction encompasses both Photosystem I (PS1) and Photosystem II (PS2).
• In PS2, the absorption of a photon excites the P680 chlorophyll molecule. This excitement leads to the loss of an electron, which is subsequently transferred to pheophytin.
• The electron then embarks on a unique trajectory, often visualized as a zigzag or ‘Z’ pattern, hence the name “Z-Scheme.”
• Within this Z-Scheme, the electron undergoes a series of redox reactions, culminating in the reduction of NADP+ to NADPH.
• Concurrently, the chemiosmotic potential is established by pumping protons across the membrane into the thylakoid lumen. This gradient drives the synthesis of ATP .

In summary, the Z-Scheme is a crucial component of the non-cyclic photochemical reactions in photosynthesis. It delineates the intricate electron flow through both photosystems, facilitating the production of essential energy molecules, NADPH and ATP , vital for the subsequent stages of photosynthesis.

Cyclic vs. Non-cyclic phosphorylation

In the intricate process of photosynthesis, photochemical reactions play a pivotal role. These reactions can be broadly categorized into cyclic and non-cyclic phosphorylation. Each type has distinct characteristics and functions. Here’s a detailed comparison between the two:

Key Insights:

• Cyclic Phosphorylation: This process involves only Photosystem I (PS1). As the name suggests, the electron flow is cyclic, meaning the electrons return to their original position after completing the cycle. Notably, this process does not lead to the oxidation of water or the generation of oxygen gas. Its primary function is to produce ATP .
• Non-cyclic Phosphorylation: This is a more complex process involving both Photosystem I (PS1) and Photosystem II (PS2). Here, electrons are transferred from water molecules to NADP+, resulting in the production of NADPH. This process leads to the oxidation of water, releasing oxygen gas as a byproduct. Both ATP and NADPH are produced, which are essential for the subsequent stages of photosynthesis.

In essence, while both cyclic and non-cyclic phosphorylation contribute to the production of ATP , only non-cyclic phosphorylation results in the generation of NADPH and oxygen gas, making it integral to the overall photosynthetic process.

2. Light independent reactions (Calvin cycle)

The Calvin Cycle, also known as the light-independent reactions, is a crucial phase of photosynthesis that operates in the stroma of chloroplasts. Contrary to its name, this cycle doesn’t directly rely on light; however, it is dependent on the ATP and NADPH produced during the light-dependent reactions.

• Carbon Fixation: The cycle commences with the fixation of a single carbon dioxide molecule to a five-carbon sugar called ribulose 1,5-bisphosphate. This reaction is facilitated by the enzyme ribulose 1,5-bisphosphate carboxylase, commonly referred to as rubisco. The immediate product is an unstable six-carbon compound, which rapidly splits into two molecules of 3-phosphoglycerate.
• Reduction Phase: The 3-phosphoglycerate molecules undergo a series of enzymatic reactions. Initially, ATP donates a phosphate group to 3-phosphoglycerate, forming 1,3-bisphosphoglycerate. Subsequently, NADPH provides electrons, converting 1,3-bisphosphoglycerate into glyceraldehyde 3-phosphate. While a portion of the produced glyceraldehyde 3-phosphate contributes to the synthesis of glucose and other sugars, the majority is utilized to regenerate ribulose 1,5-bisphosphate.
• Regeneration of Ribulose 1,5-bisphosphate: The remaining glyceraldehyde 3-phosphate undergoes a complex series of enzymatic reactions, resulting in the production of ribulose 1,5-bisphosphate. This regeneration ensures the continuity of the Calvin Cycle.

Overall Reaction: 3 C O 2​+9 A TP +6 N A D P H +6 H +→ g l ycer a l d e h y d e −3− p h os p ha t e ( G 3 P )+9 A D P +8 P i +6 N A D P ++3 H 2​ O

To synthesize one molecule of glucose, which contains six carbon atoms, the Calvin Cycle must operate six times, fixing six molecules of carbon dioxide.

In essence, the Calvin Cycle is a metabolic pathway that transforms carbon dioxide and other compounds into glucose, providing energy and structural integrity to plants. This intricate process underscores the importance of both light-dependent and light-independent reactions in sustaining life on Earth.

Order and kinetics of Photosynthesis

Photosynthesis, a fundamental biological process, is an intricate sequence of events that culminates in the conversion of light energy into chemical energy in the form of glucose. Understanding the order and kinetics of photosynthesis is crucial to unraveling the mechanisms that drive this essential phenomenon. This informative discourse provides insight into the sequential stages and time scales involved in the photosynthetic process, as outlined below.

Stage 1: Energy Transfer in Antenna Chlorophyll (Thylakoid Membranes)

The inception of photosynthesis begins with the absorption of light energy by chlorophyll and other pigments located in the antenna complex of thylakoid membranes. This critical step occurs with astonishing rapidity, unfolding on the femtosecond to picosecond timescale. During this minuscule time frame, the excited electrons within the chlorophyll molecules undergo rapid energy transfer, initiating the photosynthetic cascade.

Stage 2: Transfer of Electrons in Photochemical Reactions (Thylakoid Membranes)

Following energy absorption, the second stage encompasses the transfer of these energized electrons through a series of photochemical reactions within the thylakoid membranes. This process operates at a slightly longer timescale, ranging from picoseconds to nanoseconds. As electrons shuttle through protein complexes, such as Photosystem II and Photosystem I , they undergo redox reactions that ultimately result in the generation of ATP and the reduction of NADP+ to NADPH.

Stage 3: Electron Transport Chain and ATP Synthesis (Thylakoid Membranes)

The third phase of photosynthesis involves the electron transport chain, which propels electrons through a series of membrane-bound protein complexes. This intricate molecular machinery operates on a timescale spanning from microseconds to milliseconds. As electrons flow through the transport chain, protons are pumped across the thylakoid membrane, establishing a proton gradient that fuels the synthesis of ATP via chemiosmotic coupling. This stage is pivotal in harnessing the energy from light and converting it into a biologically useful form.

Stage 4: Carbon Fixation and Export of Stable Products

The culmination of photosynthesis transpires in the fourth stage, where the acquired ATP and NADPH molecules, along with carbon dioxide, are utilized for the fixation of carbon into organic compounds. This final, but no less intricate, phase operates on a timescale ranging from milliseconds to seconds. The Calvin-Benson cycle, a series of enzyme-catalyzed reactions, assimilates carbon dioxide and generates sugars, primarily glucose, which serve as the ultimate product of photosynthesis. These stable products are subsequently exported to various parts of the plant for energy storage and growth.

In conclusion, the order and kinetics of photosynthesis encompass a meticulously orchestrated sequence of events, spanning a wide range of time scales from femtoseconds to seconds. This process showcases the remarkable efficiency of nature in harnessing light energy to sustain life on Earth, underlining its significance in the realm of biological science.

Carbon Concentrating Mechanisms in Photosynthesis

In the realm of photosynthesis, carbon concentrating mechanisms (CCMs) play a pivotal role in optimizing the carbon fixation process, especially in environments with fluctuating carbon dioxide (CO2) levels. These mechanisms are primarily observed in certain angiosperm families and are categorized based on their operational strategies.

1. C4 Photosynthesis: The C4 pathway, also known as the Hatch and Slack cycle, is a specialized mechanism observed in approximately 4% of angiosperm families, notably Poaceae and Cyperaceae. It was elucidated by scientists Hatch and Slack, who studied its manifestation in maize plants.

• Mechanism: In C4 plants, photosynthesis is spatially separated into two cell types: mesophyll cells and bundle sheath cells. The initial CO2 fixation occurs in the mesophyll cells, where CO2 is combined with phosphoenolpyruvate (PEP) by the enzyme PEP carboxylase, producing a four-carbon compound, oxaloacetic acid or malate. This compound is then transported to the bundle sheath cells, where it undergoes decarboxylation, releasing CO2. This CO2 is subsequently fixed into glucose through the conventional C3 cycle.
• Significance: The C4 mechanism is an adaptive strategy for plants in semi-arid regions. Under high temperatures and light conditions, these plants can efficiently fix CO2, even when stomata are partially closed to minimize water loss. This spatial separation reduces the oxygenase activity of RuBisCo, thereby decreasing photorespiration and enhancing carbon fixation.

2. CAM Photosynthesis: Crassulacean Acid Metabolism (CAM) is another carbon concentrating mechanism predominantly found in xerophytes like cacti and succulents, with around 16,000 species employing this strategy.

• Mechanism: Unlike C4 plants that exhibit spatial separation, CAM plants demonstrate a temporal separation of CO2 uptake and fixation. During the night, when the stomata are open, CO2 is fixed into malate by PEP carboxylase. During the day, when the stomata are closed, malate is decarboxylated to release CO2, which is then fixed through the C3 cycle.
• Significance: This mechanism allows CAM plants to efficiently conduct photosynthesis under water-limited conditions, as they can take up CO2 during cooler nights and minimize water loss during the day.

Aquatic Adaptations: In aquatic environments, cyanobacteria exhibit a unique carbon concentrating mechanism. They possess specialized structures called carboxysomes, which enrich the CO2 concentration around the RuBisCo enzyme. The enzyme carbonic anhydrase within these carboxysomes can release CO2 from dissolved bicarbonate ions, ensuring efficient carbon fixation.

In summary, carbon concentrating mechanisms are adaptive strategies that enhance the efficiency of photosynthesis under varying environmental conditions. Whether through spatial or temporal separation, or specialized cellular structures, these mechanisms ensure optimal carbon fixation, catering to the diverse needs of plants across different habitats.

Regulation of the cycle

Photosynthesis is not possible in the night, however, glycolysis, a process that utilizes the same reactions as those in the Calvin-Benson cycles, with the exception of the reverse, takes place. This means that certain steps in the cycle would be inefficient when they are allowed to take place in darkness, as they could impede the process of glycolysis. In this regard, certain enzymes in the Calvin-Benson cycle can be “turned off” (i.e. they become inactive) in darkness.

In the absence of sunlight, changes in physiological conditions often require adjustments to the rate of reaction in the Calvin-Benson cycle such that enzymes that are involved in some reactions alter their catalytic activities. These changes in enzyme activity are typically caused through changes in the levels of chloroplast components such as reduced ferredoxin and acids and the soluble components (e.g., Pi and magnesium ions).

Products of Photosynthesis

Photosynthesis, the fundamental process by which plants convert light energy into chemical energy, yields a variety of essential products that sustain life on Earth. These products can be categorized based on the specific reactions involved:

• ATP (Adenosine Triphosphate) : A primary energy currency of cells, facilitating energy transfer for various cellular processes.
• NADPH (Nicotinamide Adenine Dinucleotide Phosphate) : A coenzyme that carries electrons, crucial for the synthesis of organic molecules.
• Oxygen (O2) : Released into the atmosphere as a byproduct when water molecules are split.
• Protons (H+ ions) : These play a role in creating a proton gradient across the thylakoid membrane, driving ATP synthesis.
• Glyceraldehyde-3-Phosphate (G3P) : A three-carbon sugar molecule, which is a precursor to glucose and other carbohydrates.
• Protons (H+ ions) : Involved in the reduction of 3-phosphoglycerate to G3P.
• Glucose ( Carbohydrates ) : The primary energy storage molecule, which can be further converted into other organic compounds or used for energy by organisms.
• Water (H2O) : Some water molecules are produced during the Calvin cycle.
• Oxygen (O2) : A vital byproduct released into the atmosphere, supporting aerobic respiration in organisms.
• Sulfur : Specifically produced in photosynthetic sulfur bacteria, contributing to the sulfur cycle in ecosystems.

These products, especially glucose and oxygen, are fundamental to the survival and growth of most organisms on Earth.

Process of Photosynthesis – Overview

Photosynthesis, a vital physiological process, transpires within specialized cellular structures termed chloroplasts. These organelles house chlorophyll, the green pigment responsible for the characteristic hue of plant leaves. The leaf’s lamina facilitates the absorption of both sunlight and carbon dioxide, essential components for photosynthesis.

This intricate process can be delineated into two primary phases based on light dependency:

• Temporal Occurrence : As the name suggests, these reactions are contingent upon sunlight and predominantly occur during daylight hours.
• Location : The thylakoid membrane, within the chloroplast, is the site for these reactions.
• Grana : Situated inside the thylakoid, grana are sac-like structures that capture and store light.
• Photosystem-I (PS-I)
• Photosystem-II (PS-II)
• Electron Excitation : Upon photon absorption by chlorophyll within the reaction center, an electron is excited and subsequently released.
• Energy Conversion : This phase culminates in the conversion of solar energy into chemical energy, yielding ATP and NADPH.
• Chemical Representation : 2H2O + 2NADP+ + 3 ADP + 3Pi → O2 + 2NADPH + 3ATP
• Alternative Names : Often referred to as the dark reaction or carbon fixation.
• Location : These reactions transpire within the stroma of the chloroplast.
• Carbon Dioxide Uptake : Plants assimilate carbon dioxide via stomata, initiating the Calvin cycle.
• Sugar Formation : Through the Calvin cycle, six carbon dioxide molecules are utilized to synthesize a single sugar molecule.
• Chemical Representation : 3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6NADP+ + 9ADP + 8Pi

Light-dependent reactions vs. light-independent reactions

Photosynthesis, the process by which plants convert light energy into chemical energy, is delineated into two primary phases: the light-dependent reactions and the light-independent reactions. Each phase plays a distinct role in the overall process, and they are characterized by their dependency on light and their respective locations within the chloroplast.

1. Light-Dependent Reactions:

• Location: These reactions transpire in the thylakoid membrane of the chloroplast.
• Dependency on Light: As the name suggests, light-dependent reactions necessitate the direct absorption of sunlight.
• Mechanism: Within the thylakoid membrane, chlorophyll and other pigments absorb photons from sunlight. This absorption triggers a series of electron transport chains, leading to the synthesis of energy-rich molecules, adenosine triphosphate ( ATP ) and nicotinamide adenine dinucleotide phosphate (NADPH).
• Outcome: The primary products of light-dependent reactions are ATP and NADPH, which store the energy harnessed from sunlight in chemical form.

2. Light-Independent Reactions (Calvin Cycle):

• Location: These reactions occur in the stroma, the fluid-filled space between the thylakoid membranes and the chloroplast envelope.
• Dependency on Light: Contrary to light-dependent reactions, the Calvin Cycle operates independently of direct light exposure, hence the designation “light-independent.”
• Mechanism: Utilizing the energy stored in ATP and NADPH, the Calvin Cycle facilitates the fixation of atmospheric carbon dioxide (CO2) into organic molecules. Through a series of enzymatic reactions, CO2 is converted into carbohydrate molecules, such as glucose.
• Outcome: The culmination of the Calvin Cycle is the synthesis of glucose and other carbohydrates, which serve as energy reservoirs for the plant and are crucial for growth and development.

Photosynthesis examples

Photosynthesis, the process by which organisms convert light energy into chemical energy, manifests in various forms across different species. Here are specific examples:

• Organisms : Green plants and oxygenic bacteria, notably cyanobacteria.
• Pigment Involved : Chlorophyll, a green pigment, plays a pivotal role in capturing light energy.
• Location : This process occurs within the thylakoids of chloroplasts.
• Reactants : Carbon dioxide and water.
• Products : Oxygen gas, glucose, and water molecules. In plants, glucose units are often linked to form compounds like starch, fructose, or sucrose.
• Organisms : Purple sulfur bacteria and green sulfur bacteria.
• Pigment Involved : While green sulfur bacteria utilize chlorophyll, purple sulfur bacteria predominantly use carotenoids as their photosynthetic pigments.
• Location : Within specialized structures in bacterial cells.
• Reactants : Carbon dioxide and hydrogen sulfide (H2S) serve as the primary reactants, replacing water.
• Products : Carbohydrates (which may not always be glucose), sulfur gas, and water molecules.
• Organisms : Red algae (Rhodophyta).
• Pigment Involved : Phycobiliproteins, especially phycoerythrin, give red algae its distinctive color and play a role in capturing light energy.
• Location : Within the chloroplasts of red algae cells.
• Products : Oxygen gas and carbohydrates. Red algae often produce floridean starch as their primary carbohydrate storage molecule.
• Organisms : Diatoms , a major group of microalgae found in oceans, waterways, and soils.
• Pigment Involved : Chlorophyll-a and chlorophyll-c, along with fucoxanthin, a brown pigment that gives diatoms their golden-brown color.
• Location : Within the chloroplasts of diatom cells, which are often encased in intricate silica shells.
• Products : Oxygen gas and carbohydrates. Diatoms store energy primarily as chrysolaminarin, a water-soluble polysaccharide.

These examples underscore the diversity of photosynthetic processes across different organisms, each adapted to their unique environments and energy requirements.

Importance of photosynthesis

• Photosynthesis serves as the fundamental energy conversion mechanism for autotrophic organisms. Through this process, they harness solar energy, converting it into chemical energy stored in the form of glucose and other carbohydrates. This self-sustenance allows them to thrive in diverse ecosystems.
• Autotrophs , primarily plants and certain bacteria, form the base of the food chain. Heterotrophic organisms, including animals and humans, rely on these primary producers for their energy and nutritional needs. Without photosynthesis, the foundation of this chain would collapse, disrupting the balance of ecosystems.
• Photosynthesis is a critical contributor to the planet’s oxygen levels. As plants and photosynthetic bacteria convert carbon dioxide into glucose, they release oxygen as a byproduct. This oxygen replenishes the atmosphere, ensuring its availability for aerobic respiration in various organisms.
• Through photosynthesis, plants play a pivotal role in the global carbon cycle. They absorb atmospheric carbon dioxide, converting it into organic compounds. This process aids in mitigating the effects of excessive carbon dioxide, which is a major greenhouse gas contributing to global warming.
• Photosynthesis facilitates various symbiotic relationships in nature. For instance, plants provide oxygen and nutrients to animals, which in turn produce carbon dioxide and other organic matter that plants utilize. This mutualistic relationship underscores the interconnectedness of life.
• The sun is the ultimate energy source for Earth. Through photosynthesis, this radiant energy is captured and transformed into a form that can be used by a myriad of organisms. This process underscores the significance of solar energy in sustaining life on the planet.

In essence, photosynthesis is not just a biological process but a cornerstone of life on Earth. It interlinks various biogeochemical cycles, supports biodiversity, and ensures the continuity of energy flow in ecosystems.

What is Artificial photosynthesis?

• Artificial photosynthesis refers to a chemically engineered process that emulates the natural mechanism by which plants, algae, and certain bacteria harness sunlight to convert water and carbon dioxide into oxygen and energy-rich carbohydrates.
• Central to artificial photosynthesis is the use of photocatalysts. These are specialized compounds designed to facilitate the oxidation-reduction reactions analogous to those in natural photosynthesis. Their role is pivotal in capturing and converting solar energy efficiently.
• The primary aim of artificial photosynthesis is the generation of solar fuels. These are energy carriers synthesized directly from sunlight, allowing for energy storage and utilization even in the absence of direct sunlight.
• One of the significant outcomes of artificial photosynthesis is the production of oxygen from water and sunlight. This process offers a sustainable and environmentally friendly approach to energy generation, minimizing carbon emissions and other pollutants.
• A crucial component of artificial photosynthesis is the photocatalytic division of water molecules. This process yields oxygen and a substantial volume of hydrogen gas, a potential clean fuel source with myriad applications.
• Beyond water splitting, artificial photosynthesis can also drive carbon reduction, mirroring the natural carbon fixation pathway. This results in the synthesis of carbohydrate molecules, providing another avenue for energy storage.
• The implications of artificial photosynthesis are vast. It holds promise in diverse fields such as photoelectrochemistry, enzyme engineering, and the development of photoautotrophic microorganisms. These applications can lead to the production of microbial biofuels and biohydrogen, offering sustainable energy solutions derived directly from sunlight.

Photosynthesis vs Cellular respiration

Photosynthesis and cellular respiration are two fundamental biochemical processes that sustain life on Earth. While they are interconnected and interdependent, they serve distinct roles in the energy dynamics of living organisms. Here, we elucidate the key differences between these two processes:

• Type : An anabolic process, which means it involves the synthesis of complex molecules from simpler ones.
• Energy Dynamics : Endergonic and endothermic, signifying that it absorbs energy.
• Type : A catabolic process, implying the breakdown of complex molecules to release energy.
• Energy Dynamics : Exergonic and exothermic, indicating that it releases energy.
• Photosynthesis : Takes place in the chloroplasts of eukaryotic phototrophic cells, specifically within the thylakoids.
• Cellular Respiration : Primarily occurs in the mitochondria of cells.
• Reactants : Carbon dioxide, water, and light energy.
• Products : Glucose (a carbohydrate), oxygen, and in some instances, water.
• Reactants : Glucose and oxygen.
• Products : Carbon dioxide, water, and energy in the form of adenosine triphosphate ( ATP ).
• Photosynthesis : 6CO2 + 6H2O (in the presence of light energy) → C6H12O6 + 6O2
• Cellular Respiration : C6H12O6 + 6O2 → 6CO2 + 6H2O
• Photosynthesis : Conducted by green plants, certain algae, and some photosynthetic bacteria.
• Cellular Respiration : A universal process that occurs in all living organisms.
• Photosynthesis : Exclusively occurs in the presence of sunlight.
• Cellular Respiration : A continuous process that does not necessitate sunlight.

Evolution of Photosynthesis

The evolution of photosynthesis is a fascinating journey through Earth’s history, representing a pivotal moment in the development of life on our planet. This process has not only shaped the composition of the Earth’s atmosphere but has also played a fundamental role in the emergence of complex life forms. In this scientific exploration, we delve into the key milestones and mechanisms underlying the evolution of photosynthesis.

Early Photosynthetic Organisms:

The fossil record provides intriguing insights into the origins of photosynthesis. Fossils of filamentous photosynthetic organisms, dating back approximately 3.4 billion years, suggest that photosynthesis may have commenced around this time. These ancient organisms likely laid the foundation for the photosynthetic processes we observe today.

Oxygenic Photosynthesis Emergence:

The most significant shift in Earth’s history was the rise of oxygenic photosynthesis, which ultimately led to the oxygenation of our planet. Geological evidence points to the emergence of oxygenic photosynthesis, notably in cyanobacteria, during the Paleoproterozoic era, roughly 2 billion years ago. This marked the inception of an era often referred to as the “oxygen catastrophe,” as oxygen levels in the atmosphere began to rise significantly.

Symbiosis and Chloroplast Origins:

One intriguing aspect of photosynthesis evolution is the symbiotic relationships that have developed between photosynthetic organisms and various life forms. Notably, corals, sponges, sea anemones, and even certain mollusks, such as Elysia viridis and Elysia chlorotica, have formed symbiotic connections with photosynthetic algae. These relationships are often attributed to the simplicity of the host organisms’ body plans and their ability to maximize surface area for photosynthesis.

Endosymbiotic Theory and Chloroplasts:

A pivotal moment in the evolution of photosynthesis occurred with the origin of chloroplasts. Chloroplasts, which bear striking similarities to photosynthetic bacteria, are thought to have originated through endosymbiosis. According to this theory, early eukaryotic cells engulfed photosynthetic bacteria, eventually forming the first plant cells. The evidence for this theory lies in the presence of chloroplast DNA, separate from the host cell’s nucleus, resembling the genetic makeup of cyanobacteria. This genetic legacy supports the notion that chloroplasts evolved from photosynthetic bacteria.

Diversity of Photosynthetic Lineages:

Photosynthesis has diversified over time, resulting in various lineages of photosynthetic organisms. These include:

• Archaeplastida (uni- and multicellular): Comprising glaucophytes, red and green algae.
• Cryptista (unicellular): Encompassing cryptophytes.
• Haptista (unicellular): Represented by haptophytes.
• Alveolata (unicellular): Incorporating dinoflagellates, chromerids, and Pseudoblepharisma.
• Stramenopila (uni- and multicellular): Encompassing ochrophytes.
• Rhizaria (unicellular): Comprising chlorarachniophytes and select Paulinella species.
• Excavata (unicellular): Including euglenids.

These lineages, whether uni- or multicellular, reveal the diversification of photosynthetic organisms and their adaptive strategies.

Prokaryotic Photosynthesis:

Early photosynthetic systems, particularly those of green and purple sulfur and green and purple nonsulfur bacteria, were likely anoxygenic and utilized various molecules, such as hydrogen, sulfur, and organic acids, as electron donors. These systems were consistent with the highly reducing conditions of the early Earth’s atmosphere. Archaea , including haloarchaea, can harness energy from the sun but do not perform oxygenic photosynthesis.

In conclusion, the evolution of photosynthesis is a captivating narrative of life’s adaptation to Earth’s changing conditions. From the emergence of early photosynthetic organisms to the rise of oxygenic photosynthesis and the formation of symbiotic relationships, photosynthesis has played a pivotal role in shaping our planet’s history and continues to be a cornerstone of life as we know it. This intricate process underscores the remarkable complexity and diversity of life on Earth.

Quiz Practice

MCQ 1: What is the primary pigment responsible for capturing light energy in photosynthesis?

A) Chlorophyll B) Carotenoid C) Xanthophyll D) Phycobilin

MCQ 2: In which organelle does photosynthesis primarily occur in plant cells?

A) Nucleus B) Mitochondria C) Chloroplast D) Endoplasmic reticulum

MCQ 3: During the light-dependent reactions of photosynthesis, what molecule is produced as a byproduct?

A) Oxygen B) Carbon dioxide C) Glucose D) Water

MCQ 4: What is the primary source of carbon dioxide for photosynthesis in most plants?

A) Soil B) Air C) Water D) Other plants

MCQ 5: Which of the following colors of light is least effective in driving photosynthesis?

A) Red B) Blue C) Green D) Yellow

MCQ 6: What is the ultimate goal of the Calvin cycle in photosynthesis?

A) Produce ATP B) Convert glucose to starch C) Generate carbon dioxide D) Synthesize glucose

MCQ 7: In C4 plants, what is the primary function of mesophyll cells?

A) Storing water B) Capturing light energy C) Fixing carbon dioxide D) Producing oxygen

MCQ 8: What gas is necessary for the opening of stomata during photosynthesis?

A) Oxygen B) Carbon dioxide C) Nitrogen D) Hydrogen

MCQ 9: Which environmental factor can limit the rate of photosynthesis?

A) High oxygen levels B) Low carbon dioxide levels C) Warm temperatures D) Bright sunlight

MCQ 10: What is the primary purpose of the light-independent reactions (Calvin cycle) in photosynthesis?

A) Generate oxygen B) Produce ATP C) Fix carbon dioxide D) Capture light energy

Where does photosynthesis take place?

In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll. Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane, that forms long folds within the organelle.

What are the reactants of photosynthesis?

The process of photosynthesis is commonly written as: 6CO2 + 6H2O → C6H12O6 + 6O2. This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products.

How are photosynthesis and cellular respiration related?

Photosynthesis is the process by which atmospheric carbon dioxide is assimilated and converted to glucose and oxygen is released. CO2 and H2O are utilised in the process. In the cellular respiration, glucose is broken down to CO2 and energy is released in the form of ATP , which is utilised in performing various metabolic processes. Oxygen is utilised in the process. Energy is stored in the process of photosynthesis, whereas it is released in the process of cellular respiration. The process of cellular respiration and photosynthesis complement each other. These processes help cells to release and store the energy respectively. They are required to keep the atmospheric balance of carbon dioxide and oxygen concentrations.

What is the equation for photosynthesis?

The process of photosynthesis is commonly written as: 6CO2 + 6H2O → C6H12O6 + 6O2

Where does photosynthesis occur?

chloroplasts

What are the products of photosynthesis?

Let’s look at the products of photosynthesis! During the process of photosynthesis plants break apart the reactants of carbon dioxide and water and recombine them to produce oxygen (O2) and a form of sugar called glucose (C6H12O6).

Why is photosynthesis important?

Photosynthesis is the main source of food on earth. It releases oxygen which is an important element for the survival of life. Without photosynthesis, there will be no oxygen on earth. The stored chemical energy in plants flows into herbivores, carnivores, predators, parasites, decomposers, and all life forms.

Which of these equations best summarizes photosynthesis? A. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy B. C6H12O6 + 6 O2 → 6 CO2 + 12 H2O C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D. 6 CO2 + 6 O2 → C6H12O6 + 6 H2O E. H2O → 2 H+ + 1/2 O2 + 2e-

Ans: C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2

What are the raw materials of photosynthesis?

The raw materials of photosynthesis, water and carbon dioxide, enter the cells of the leaf. Oxygen, a by-product of photosynthesis, and water vapor exit the leaf.

Which gas is removed from the atmosphere during photosynthesis?

Photosynthesis removes CO2 from the atmosphere and replaces it with O2.

Which of the following sequences correctly represents the flow of electrons during photosynthesis? A. NADPH → O2 → CO2 B. H2O → NADPH → Calvin cycle C. NADPH → chlorophyll → Calvin cycle D. H2O → photosystem I → photosystem II

The correct option is B H2O → NADPH → Calvin cycle Electrons flow from water through the photosystem II, electron transport chain, and photosystem I to NADP+. The electrons of NADPH thus formed are then used in the Calvin cycle.

What organelle does photosynthesis occur in

What are the inputs of photosynthesis.

In photosynthesis, water, carbon dioxide, and energy in the form of sunlight are inputs, and the outputs are glucose and oxygen.

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• Leegood, R. C. (2004). Photosynthesis. Encyclopedia of Biological Chemistry, 330–335. doi:10.1016/b0-12-443710-9/00487-7
• Boyer, R. (2006). Concepts in Biochemistry , 3rd edition. John Wiley & Sons.
• Heldt, H. W. (2005). Plant Biochemistry , 3rd edition. Academic Press.
• Martin, W. F., Garg, S., & Zimorski, V. (2015). Endosymbiotic theories for eukaryote origin. Philosophical Transactions of the Royal Society B: Biological Sciences , 370(1678), 20140330. doi:10.1098/rstb.2014.0330
• Milne, B. F., Toker, Y., Rubio, A., & Nielsen, S. B. (2015). Unraveling the Intrinsic Color of Chlorophyll. Angewandte Chemie International Edition , 54(7), 2170-2173. doi:10.1002/anie.201410899
• Gao, J., Wang, H., Yuan, Q., & Feng, Y. (2018). Structure and Function of the Photosystem Supercomplexes. Frontiers in Plant Science , 9. doi:10.3389/fpls.2018.00357
• Rutherford, A. W., & Faller, P. (2003, January). “Photosystem II: evolutionary perspectives.” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences , 358(1429), 245–253. doi:10.1098/rstb.2002.1186. PMC 1693113. PMID 12594932.
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ENCYCLOPEDIC ENTRY

Photosynthesis.

Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.

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Learning materials, instructional links.

• Photosynthesis (Google doc)

Most life on Earth depends on photosynthesis .The process is carried out by plants, algae, and some types of bacteria, which capture energy from sunlight to produce oxygen (O 2 ) and chemical energy stored in glucose (a sugar). Herbivores then obtain this energy by eating plants, and carnivores obtain it by eating herbivores.

The process

During photosynthesis, plants take in carbon dioxide (CO 2 ) and water (H 2 O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.

Chlorophyll

Inside the plant cell are small organelles called chloroplasts , which store the energy of sunlight. Within the thylakoid membranes of the chloroplast is a light-absorbing pigment called chlorophyll , which is responsible for giving the plant its green color. During photosynthesis , chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.

Light-dependent Reactions vs. Light-independent Reactions

While there are many steps behind the process of photosynthesis, it can be broken down into two major stages: light-dependent reactions and light-independent reactions. The light-dependent reaction takes place within the thylakoid membrane and requires a steady stream of sunlight, hence the name light- dependent reaction. The chlorophyll absorbs energy from the light waves, which is converted into chemical energy in the form of the molecules ATP and NADPH . The light-independent stage, also known as the Calvin cycle , takes place in the stroma , the space between the thylakoid membranes and the chloroplast membranes, and does not require light, hence the name light- independent reaction. During this stage, energy from the ATP and NADPH molecules is used to assemble carbohydrate molecules, like glucose, from carbon dioxide.

C3 and C4 Photosynthesis

Not all forms of photosynthesis are created equal, however. There are different types of photosynthesis, including C3 photosynthesis and C4 photosynthesis. C3 photosynthesis is used by the majority of plants. It involves producing a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose. C4 photosynthesis, on the other hand, produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle. A benefit of C4 photosynthesis is that by producing higher levels of carbon, it allows plants to thrive in environments without much light or water. The National Geographic Society is making this content available under a Creative Commons CC-BY-NC-SA license . The License excludes the National Geographic Logo (meaning the words National Geographic + the Yellow Border Logo) and any images that are included as part of each content piece. For clarity the Logo and images may not be removed, altered, or changed in any way.

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Related Resources

• Biology Article

Photosynthesis

Photosynthesis is a process by which phototrophs convert light energy into chemical energy, which is later used to fuel cellular activities. The chemical energy is stored in the form of sugars, which are created from water and carbon dioxide.

Table of Contents

• What is Photosynthesis?
• Site of photosynthesis

Photosynthesis definition states that the process exclusively takes place in the chloroplasts through photosynthetic pigments such as chlorophyll a, chlorophyll b, carotene and xanthophyll. All green plants and a few other autotrophic organisms utilize photosynthesis to synthesize nutrients by using carbon dioxide, water and sunlight. The by-product of the photosynthesis process is oxygen.Let us have a detailed look at the process, reaction and importance of photosynthesis.

What Is Photosynthesis in Biology?

The word “ photosynthesis ” is derived from the Greek words  phōs  (pronounced: “fos”) and σύνθεσις (pronounced: “synthesis “) Phōs means “light” and σύνθεσις   means, “combining together.” This means “ combining together with the help of light .”

Photosynthesis also applies to other organisms besides green plants. These include several prokaryotes such as cyanobacteria, purple bacteria and green sulfur bacteria. These organisms exhibit photosynthesis just like green plants.The glucose produced during photosynthesis is then used to fuel various cellular activities. The by-product of this physio-chemical process is oxygen.

A visual representation of the photosynthesis reaction

• Photosynthesis is also used by algae to convert solar energy into chemical energy. Oxygen is liberated as a by-product and light is considered as a major factor to complete the process of photosynthesis.
• Photosynthesis occurs when plants use light energy to convert carbon dioxide and water into glucose and oxygen. Leaves contain microscopic cellular organelles known as chloroplasts.
• Each chloroplast contains a green-coloured pigment called chlorophyll. Light energy is absorbed by chlorophyll molecules whereas carbon dioxide and oxygen enter through the tiny pores of stomata located in the epidermis of leaves.
• Another by-product of photosynthesis is sugars such as glucose and fructose.
• These sugars are then sent to the roots, stems, leaves, fruits, flowers and seeds. In other words, these sugars are used by the plants as an energy source, which helps them to grow. These sugar molecules then combine with each other to form more complex carbohydrates like cellulose and starch. The cellulose is considered as the structural material that is used in plant cell walls.

Where Does This Process Occur?

Chloroplasts are the sites of photosynthesis in plants and blue-green algae.  All green parts of a plant, including the green stems, green leaves,  and sepals – floral parts comprise of chloroplasts – green colour plastids. These cell organelles are present only in plant cells and are located within the mesophyll cells of leaves.

Also Read:  Photosynthesis Early Experiments

Photosynthesis Equation

Photosynthesis reaction involves two reactants, carbon dioxide and water. These two reactants yield two products, namely, oxygen and glucose. Hence, the photosynthesis reaction is considered to be an endothermic reaction. Following is the photosynthesis formula:

Unlike plants, certain bacteria that perform photosynthesis do not produce oxygen as the by-product of photosynthesis. Such bacteria are called anoxygenic photosynthetic bacteria. The bacteria that do produce oxygen as a by-product of photosynthesis are called oxygenic photosynthetic bacteria.

Structure Of Chlorophyll

The structure of Chlorophyll consists of 4 nitrogen atoms that surround a magnesium atom. A hydrocarbon tail is also present. Pictured above is chlorophyll- f,  which is more effective in near-infrared light than chlorophyll- a

Chlorophyll is a green pigment found in the chloroplasts of the  plant cell   and in the mesosomes of cyanobacteria. This green colour pigment plays a vital role in the process of photosynthesis by permitting plants to absorb energy from sunlight. Chlorophyll is a mixture of chlorophyll- a  and chlorophyll- b .Besides green plants, other organisms that perform photosynthesis contain various other forms of chlorophyll such as chlorophyll- c1 ,  chlorophyll- c2 ,  chlorophyll- d and chlorophyll- f .

Also Read:   Biological Pigments

Process Of Photosynthesis

At the cellular level,  the photosynthesis process takes place in cell organelles called chloroplasts. These organelles contain a green-coloured pigment called chlorophyll, which is responsible for the characteristic green colouration of the leaves.

As already stated, photosynthesis occurs in the leaves and the specialized cell organelles responsible for this process is called the chloroplast. Structurally, a leaf comprises a petiole, epidermis and a lamina. The lamina is used for absorption of sunlight and carbon dioxide during photosynthesis.

Structure of Chloroplast. Note the presence of the thylakoid

“Photosynthesis Steps:”

• During the process of photosynthesis, carbon dioxide enters through the stomata, water is absorbed by the root hairs from the soil and is carried to the leaves through the xylem vessels. Chlorophyll absorbs the light energy from the sun to split water molecules into hydrogen and oxygen.
• The hydrogen from water molecules and carbon dioxide absorbed from the air are used in the production of glucose. Furthermore, oxygen is liberated out into the atmosphere through the leaves as a waste product.
• Glucose is a source of food for plants that provide energy for  growth and development , while the rest is stored in the roots, leaves and fruits, for their later use.
• Pigments are other fundamental cellular components of photosynthesis. They are the molecules that impart colour and they absorb light at some specific wavelength and reflect back the unabsorbed light. All green plants mainly contain chlorophyll a, chlorophyll b and carotenoids which are present in the thylakoids of chloroplasts. It is primarily used to capture light energy. Chlorophyll-a is the main pigment.

The process of photosynthesis occurs in two stages:

• Light-dependent reaction or light reaction
• Light independent reaction or dark reaction

Stages of Photosynthesis in Plants depicting the two phases – Light reaction and Dark reaction

Light Reaction of Photosynthesis (or) Light-dependent Reaction

• Photosynthesis begins with the light reaction which is carried out only during the day in the presence of sunlight. In plants, the light-dependent reaction takes place in the thylakoid membranes of chloroplasts.
• The Grana, membrane-bound sacs like structures present inside the thylakoid functions by gathering light and is called photosystems.
• These photosystems have large complexes of pigment and proteins molecules present within the plant cells, which play the primary role during the process of light reactions of photosynthesis.
• There are two types of photosystems: photosystem I and photosystem II.
• Under the light-dependent reactions, the light energy is converted to ATP and NADPH, which are used in the second phase of photosynthesis.
• During the light reactions, ATP and NADPH are generated by two electron-transport chains, water is used and oxygen is produced.

The chemical equation in the light reaction of photosynthesis can be reduced to:

2H 2 O + 2NADP+ + 3ADP + 3Pi → O 2 + 2NADPH + 3ATP

Dark Reaction of Photosynthesis (or) Light-independent Reaction

• Dark reaction is also called carbon-fixing reaction.
• It is a light-independent process in which sugar molecules are formed from the water and carbon dioxide molecules.
• The dark reaction occurs in the stroma of the chloroplast where they utilize the NADPH and ATP products of the light reaction.
• Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the Calvin photosynthesis cycle.
• In the Calvin cycle , the ATP and NADPH formed during light reaction drive the reaction and convert 6 molecules of carbon dioxide into one sugar molecule or glucose.

The chemical equation for the dark reaction can be reduced to:

3CO 2 + 6 NADPH + 5H 2 O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi

* G3P – glyceraldehyde-3-phosphate

Calvin photosynthesis Cycle (Dark Reaction)

Also Read:  Cyclic And Non-Cyclic Photophosphorylation

Importance of Photosynthesis

• Photosynthesis is essential for the existence of all life on earth. It serves a crucial role in the food chain – the plants create their food using this process, thereby, forming the primary producers.
• Photosynthesis is also responsible for the production of oxygen – which is needed by most organisms for their survival.

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1. what is photosynthesis explain the process of photosynthesis., 2. what is the significance of photosynthesis, 3. list out the factors influencing photosynthesis., 4. what are the different stages of photosynthesis, 5. what is the calvin cycle, 6. write down the photosynthesis equation..

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Please What Is Meant By 300-400 PPM

PPM stands for Parts-Per-Million. It corresponds to saying that 300 PPM of carbon dioxide indicates that if one million gas molecules are counted, 300 out of them would be carbon dioxide. The remaining nine hundred ninety-nine thousand seven hundred are other gas molecules.

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What Are the Reactants & Products in the Equation for Photosynthesis?

Organelles Involved in Photosynthesis

Photosynthesis is the process by which plants, and some bacteria, use solar energy to produce sugar. This process converts light energy to chemical energy, which is stored in the sugars. This process is important for two reasons. First, photosynthesis provides the energy that is used by all other organisms to survive. Second, photosynthesis removes carbon dioxide from the atmosphere, replacing it with life-sustaining oxygen. The process involves three basic reactants and produces three key products.

TL;DR (Too Long; Didn't Read)

The reactants for photosynthesis are light energy, water, carbon dioxide and chlorophyll, while the products are glucose (sugar), oxygen and water.

Photosynthesis Reactants

The photosynthetic process requires several simple reactants. Water is the first required reactant. The plant acquires water through its root system. The next required reactant is carbon dioxide. The plant absorbs this gas through its leaves. The final required reactant is light energy. The plant absorbs this energy through green pigments, called chlorophyll. This chlorophyll is located in the plant's chloroplasts.

Products of Photosynthesis

The photosynthetic process produces several products. The first product, and primary reason for the process, is simple sugar. This sugar, called glucose, is the end result of the conversion of solar energy to chemical energy. It represents stored energy that can be used by the plant, or consumed by other organisms. Oxygen is also a product of photosynthesis. This oxygen is released into the atmosphere through the plant’s leaves. Water is also a product of photosynthesis. This water is produced from the oxygen atoms in the carbon dioxide molecules. The oxygen molecules released into the atmosphere come exclusively from the original water molecules, not from the carbon dioxide molecules.

Light-Dependent Process

Photosynthesis is a two-stage process. The first stage is called the light-dependent process, or light reactions, because it requires sunlight. During this stage, light energy is converted into adenosine triphosphate (ATP) and NADPH. The ATP represents stored chemical energy. These products of the light reaction are then used by the plant during the second stage of the photosynthesis process.

Light-Independent Process

The second stage of the photosynthesis process is the light-independent process, or dark reactions. During this stage, the ATP and NADPH are used to break chemical bonds and form new ones. The bonds of the carbon dioxide molecules are broken; this allows the carbon atoms to be bonded to some of the water molecules to form glucose. The oxygen atoms from the carbon dioxide are bonded to free hydrogen atoms; this bonding produces water. The free oxygen atoms from the original water molecules are released to the atmosphere.

The Overall Process

When viewed as a whole, the photosynthetic process utilizes 12 water molecules, six carbon dioxide molecules and light energy to produce one glucose molecule, six water molecules and six oxygen molecules. This can be represented by the following chemical equation:

It is important to remember that the resulting oxygen is produced from the original water molecules, not the carbon dioxide. This distinction becomes important when considering anoxygenic photosynthesis.

Related Articles

How do plant cells obtain energy, what are light dependent reactions, what are light independent reactions, why is water important to photosynthesis, what happens in the light reaction of photosynthesis, what provides electrons for the light reactions, materials needed for photosynthesis, how does a plant convert light energy to chemical energy, phases of photosynthesis & its location, what is the end product of photosynthesis, when does respiration occur in plants, why do plants need the sun, difference between aerobic & anaerobic cellular respiration..., chemical ingredients of photosynthesis, what is the sun's role in photosynthesis, how oxygen gas is produced during photosynthesis, sequence stages in photosynthesis, what is nadph in photosynthesis, how does photosynthesis work in plants.

• University of Illinois at Urbana-Champaign; The Photosynthetic Process; John Whitmarsh, Ph.D., and Govindjee, Ph.D.

About the Author

Doug Bennett has been researching and writing nonfiction works for more than 20 years. His books have been distributed worldwide and his articles have been featured in numerous websites, newspapers and regional publications. Bennett's background includes experience in law enforcement, the military, sound reinforcement and vehicle repair/maintenance.

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AP®︎/College Biology

Course: ap®︎/college biology   >   unit 3.

• Photosynthesis

Intro to photosynthesis

• Breaking down photosynthesis stages
• Conceptual overview of light dependent reactions
• The light-dependent reactions
• The Calvin cycle
• Photosynthesis evolution
• Photosynthesis review

Introduction

What is photosynthesis.

• Energy. The glucose molecules serve as fuel for cells: their chemical energy can be harvested through processes like cellular respiration and fermentation , which generate adenosine triphosphate— ATP ‍   , a small, energy-carrying molecule—for the cell’s immediate energy needs.
• Fixed carbon. Carbon from carbon dioxide—inorganic carbon—can be incorporated into organic molecules; this process is called carbon fixation , and the carbon in organic molecules is also known as fixed carbon . The carbon that's fixed and incorporated into sugars during photosynthesis can be used to build other types of organic molecules needed by cells.

The ecological importance of photosynthesis

• Photoautotrophs use light energy to convert carbon dioxide into organic compounds. This process is called photosynthesis.
• Chemoautotrophs extract energy from inorganic compounds by oxidizing them and use this chemical energy, rather than light energy, to convert carbon dioxide into organic compounds. This process is called chemosynthesis.
• Photoheterotrophs obtain energy from sunlight but must get fixed carbon in the form of organic compounds made by other organisms. Some types of prokaryotes are photoheterotrophs.
• Chemoheterotrophs obtain energy by oxidizing organic or inorganic compounds and, like all heterotrophs, get their fixed carbon from organic compounds made by other organisms. Animals, fungi, and many prokaryotes and protists are chemoheterotrophs.

Leaves are sites of photosynthesis

The light-dependent reactions and the calvin cycle.

• The light-dependent reactions take place in the thylakoid membrane and require a continuous supply of light energy. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP ‍   —an energy storage molecule—and NADPH ‍   —a reduced (electron-bearing) electron carrier. In this process, water molecules are also converted to oxygen gas—the oxygen we breathe!
• The Calvin cycle , also called the light-independent reactions , takes place in the stroma and does not directly require light. Instead, the Calvin cycle uses ATP ‍   and NADPH ‍   from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars—glyceraldehyde-3-phosphate, or G3P, molecules—which join up to form glucose.

Photosynthesis vs. cellular respiration

Attribution.

• “ Overview of Photosynthesis ” by OpenStax College, Biology, CC BY 3.0 . Download the original article for free at http://cnx.org/contents/5bb72d25-e488-4760-8da8-51bc5b86c29d@8 .
• “ Overview of Photosynthesis ” by OpenStax College, Concepts of Biology, CC BY 3.0 . Download the original article for free at http://cnx.org/contents/[email protected] .

Works cited:

• "Great Oxygenation Event." Wikipedia. Last modified July 17, 2016. https://en.wikipedia.org/wiki/Great_Oxygenation_Event .

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ORIGINAL RESEARCH article

Water deficit differentially modulates leaf photosynthesis and transpiration of fungus-tolerant muscadinia x vitis hybrids.

• 1 UE Pech Rouge, Univ Montpellier, INRAE, Gruissan, France
• 2 UMR LEPSE, Univ Montpellier, INRAE, CIRAD, Institut Agro Montpellier, Montpellier, France
• 3 Departamento de Producción Agrícola, Facultad de Ciencias Agronómicas, Universidad de Chile, Santiago, Chile

Screening for drought performance among novel fungi-tolerant grapevine genotypes is a key point to consider in semiarid regions where water scarcity is a common problem during fruit ripening period. It is therefore important to evaluate the genotypes’ responses at the level of carbon metabolism and water demand, under water deficit conditions. This study aimed to characterize leaf and plant water use efficiency (respectively named WUEi and WUEpl) of novel INRAE fungi-tolerant genotypes (including LowSugarBerry (LSB) genotypes), under mild and high-water deficit (WD) and to decipher the photosynthetic parameters leading to higher WUEi. For this purpose, experiments were conducted on potted plants during one season using a phenotyping platform. Two stabilized soil moisture capacity (SMC) conditions, corresponding to mild (SMC 0.6) and high (SMC 0.3) WD, were imposed from the onset of berry ripening until the physiological ripeness stage, which was defined as the point at which fruits reach their maximum solutes and water content. At the whole plant level, all genotypes increased WUEpl under high WD. The highest WUEpl was reached for 3176N, which displayed both a high rate of non-structural carbon accumulation in fruits due to high fruit-to-leaf ratio and low plant transpiration because of low total leaf area. However, when normalizing the fruit-to-leaf ratio among the genotypes, G14 reached the highest normalized WUEpl_n under high WD. At the leaf level, WUEi also increased under high WD, with the highest value attained for G14 and 3176N and the lowest value for Syrah. The higher WUEi values for all genotypes compared to Syrah were associated to higher levels of photosynthesis and changes in light-harvesting efficiency parameters (Φ CO2 , qP and qN), while no clear trend was apparent when considering the photosynthetic biochemical parameters (Vcmax, Jmax). Finally, a positive correlation between leaf and plant WUE was observed regardless of genotypes. This study allowed us to classify grapevine genotypes based on their grapes primary metabolite accumulation and water consumption during the critical sugar-loading period. Additionally, the study highlighted the potential drought adaptation mechanism of the LSB genotypes.

1 Introduction

Grapevines are a prominent global fruit crop, largely cultivated in semi-arid regions with rainfed or under-deficit irrigation systems. Because of climate change, several viticultural regions are currently encountering more frequent and severe droughts ( Santillán et al., 2020 ), with significant impacts on the vineyards’ resilience, grape yield and composition ( Van Leeuwen et al., 2019 ; Santillán et al., 2020 ). With an emphasis on more eco-friendly wine and grape production that uses fewer chemical inputs in vineyards, challenges such as fungal diseases, including downy and powdery mildews, sums to this challenge. So, it becomes urgent to propose varietal innovations combining both tolerance to fungal diseases and water deficit (WD). Despite numerous breeding programs proposing new disease-tolerant hybrids ( Yobrégat, 2018 ), there is still a lack of characterization of these genotypes’ response to abiotic factors, such as drought.

When screening for drought performance among grapevine genotypes, it is crucial to consider both the carbon metabolism and water demand responses to WD. The water use efficiency (WUE) has been widely recognized as a useful parameter ( Hoover et al., 2023 ) when seeking for vineyard sustainability ( Tomás et al., 2012 ), especially under adverse climate change conditions like drought ( Andreu-Hayles et al., 2011 ; Gago et al., 2014 ). The WUE is defined as the balance between the carbon gain and water loss, and it can be measured at different scales, from leaf to ecosystem and at different time frames, from seconds to years ( Medrano et al., 2015a ; Hoover et al., 2023 ). At the leaf level, it is calculated as the ratio of net photosynthesis (An) to stomatal conductance (gs) (WUEi) or to transpiration (E) (WUEinst). At the plant level WUE can be assessed as the ratio of plant carbon gain to total transpired water (WUEpl) ( Flexas et al., 2010 ; Hoover et al., 2023 ). Carbon isotopic discrimination analysis (δC 13 ), in grapes, is an integrative indicator of WUEi during grape maturation, and might be considered as a proxy to plant WUE during ripening ( Santesteban et al., 2015 ). To assess ecosystem WUE over longer time frames, indicators such as radial wood growth, δC 13 , and eddy covariance are commonly used ( Tang et al., 2015 ; Medlyn et al., 2017 ; Gong et al., 2022 ).

High genotypic variability in grapevine WUEi under WD ( Bota et al., 2001 , Bota et al., 2016 ; Gutiérrez-Gamboa et al., 2019 ; Wilhelm de Almeida et al., 2023a ) and on δC 13 ( Tomás et al., 2014 ; Bchir et al., 2016 ; Bota et al., 2016 ; Jacinto et al., 2023 ) has been reported, mostly associated with contrasting gs regulations ( Tomás et al., 2014 ). Although all cultivars decrease stomatal conductance under WD, the sensitivity of the stomatal control under WD differs significantly. This variation has been adopted for genotype classification, distinguishing those tending to maintain stomata open at high levels of WD resulting in a decrease in leaf water potential (near anisohydric), from those characterized by stringent stomata control, thereby maintaining the leaf water potential at a high level (near isohydric) ( Schultz, 1996 , Schultz, 2000 ). However, this classification can vary, leading to controversial results for the same cultivar, mainly due to differences in growing conditions, the hydraulic conductance control on gs and the degree of WD ( Martínez-Vilalta and Garcia-Forner, 2017 ; Hochberg et al., 2018 ).

Enhancing WUEi under WD can also be achieved by investigating genotypic regulations on photosynthesis ( Medrano et al., 2002 ; Flexas et al., 2010 ; Gago et al., 2014 ; Mathias and Thomas, 2021 ). For instance, Mathias and Thomas, 2021 showed that the consistent increase in WUEi in several woody species across the globe were mainly related to stimulated An and not to gs reductions. Although stomatal limitations account for most of the An variation under WD, there are also non-stomatal limitations to consider, such as those linked to light harvesting efficiency and biochemical processes ( Gago et al., 2014 ). Under no light limiting conditions, factors such as mesophyll conductance (gm), Rubisco (RuBP) activity and carboxylation efficiency (Vcmax), RuBP regeneration (maximum electron transport rate, Jmax) and the maximum rate of triose-P use (TPU), are all vital biochemical processes that play a major role on An rates ( Flexas et al., 2016 ; Urban et al., 2017 ). Yet, it has been observed that WD negatively impacts Vcmax, Jmax and gm ( Lawlor and Tezara, 2009 ; Villalobos-González et al., 2022 ), and that such impacts were genotype dependent in grapevine ( Tomás et al., 2014 ; Villalobos-González et al., 2022 ).

It is important to have in mind that a higher WUEi under WD does not always translate into increased WUEpl. This is due to different factors impacting WUE at the leaf and plant level. For instance, WUEi is highly dependent on vapor pressure deficit (VPD), temperature and air CO 2 concentration ( Hatfield and Dold, 2019 ; Mathias and Thomas, 2021 ) because of their impact on gs ( Zufferey et al., 2000 ; Prieto et al., 2010 ; Greer, 2017 ). At the plant level, pruning and canopy management play a key role on the leaf to fruit balance and organ microclimate, thus impacting the total carbon gain and water loss ( Flexas et al., 2010 ; Prieto et al., 2012 ; Sexton et al., 2021 ). Previous studies reported a large variability of WUEpl among genotypes ( Tomás et al., 2012 ). However, the expected drought-induced increase in this trait was not always observed ( Poni et al., 2009 ; Tomás et al., 2012 ). When compared to WUEi and δC 13 studies, there are much fewer studies focusing on grapevine WUEpl under WD. This might be due to the difficulties in quantifying total carbon gain and water losses at the whole plant level over the cropping season, and adds up to the complexity of factors contributing to WUEpl.

Furthermore, when coupling both WD and high light conditions, plants will tend to avoid excessive light-related damage, by activating photoprotective mechanisms such as energy dissipation as heat ( Malnoë, 2018 ) and photorespiration ( Villalobos-González et al., 2022 ). As for energy dissipation, two useful parameters associated to chlorophyll fluorescence can be used, qP which reflects the efficiency of photosystem II (PSII) in converting light energy into chemical energy during photosynthesis (proportion of PSII reaction centers open), and qN, which is related to thermal dissipation ( Murchie and Lawson, 2013 ).

In this context, the present study aims to classify and characterize the performance of new fungal disease-tolerant varieties, including LSB genotypes which present lowered C demands in fruits ( Bigard et al., 2022 ) under controlled conditions on potted plants under mild and high WD. It is hypothesized that novel fungi-tolerant genotypes, which include non V. vinifera genetic background could exhibit different responses to WD compared to V. vinifera cv. Syrah, a widely grown variety with well-documented performance characteristics. In particular, the WUE rates at leaf and plant levels were compared and the underlying impact of the photosynthetic machinery on the leaf WUE was addressed. We have worked with mild and high water deficit conditions, based on the real conditions of grapevine cultivation. Indeed, grapevines are grown worldwide under conditions of inherent water deficit, especially during the critical period from veraison to harvest, which coincides with hotter and drier conditions of summer. The simulation of these suboptimal water conditions in our study is essential for understanding grapevine responses to stress and adapting them for improved vineyard management.

2 Materials and methods

2.1 overall plant material and growing conditions.

The plant material consisted of five fungus disease-tolerant scions of grapevine, Floreal, 3176N, 3159B, G5 and G4, which are V. vinifera x M. rotundifolia derivative hybrids ( Wilhelm de Almeida et al., 2023a ), where the latter two display the LSB trait. The V. vinifera L. var. ‘Syrah’ was adopted as the control. All plants were three years old and grafted on 140 Ruggeri rootstock. Plants were installed in 9 L (0.19 m diameter x 0.4 m high) pots filled with a substrate composed of clay (170 kg m -3 ) and peat (50% of frozen black peat and 50% of white peat). Each plant was spur pruned to keep two proleptic axes. Thus, two annual shoots with all the secondary axes, and two to three clusters per plant were retained. A total of 10 plants per genotype were assessed, resulting in population size of 60 plants.

From budburst until the start of veraison (defined as 10% of softened berries) plants were cultivated outside and managed to avoid any mineral/water deficit or pest/disease development. Fertilization consisted of a nutritive solution composed of 2.2% nitrogen 1.6% P 2 O 5 , 6.4% K 2 O, 1.6% MgO and 3.2% SO 3 , with a proportion of nutritive solution to water of 0.2%. Two inputs of iron fertilization (1.1 g Fe per plant) were performed, at 15 and 30 days after budburst.

At veraison and until the conclusion of the experiment, plants were transferred into the Phenodyn phenotyping platform to impose the targeted water treatments ( https://www6.montpellier.inrae.fr/lepse/Plateformes-de-phenotypage-M3P ). Phenodyn is an automated greenhouse equipped with a set of climatic sensors that measure light intensity, relative humidity, air temperature and VPD every minute. Each plant is equipped with a connected scale continuously measuring weight changes and an automatic dripper able to add precise amounts of water based on predetermined soil water contents target ( Sadok et al., 2007 ). During the ripening period, at 10 days after veraison (DAV) a third application of iron was made (1.1 g Fe per plant) and an input of 3 g of Osmocote per plant (0.5 g of N per plant). Relative humidity, air temperature and VPD were respectively 62%, 27 °C and 1.4 kPa during the day, and 75%, 21 °C and 0.7 kPa during the night. The photosynthetic photon flux density (PPFD) during the day (from 6:00 h to 19:00 h) was 997 μmol m -2 s -1 on average.

2.2 Water treatments

Before veraison plants were watered to meet climatic demand. They were irrigated twice a day (10h00 and 14h00) from budburst until flowering and five times a day (8h00, 10h00, 14h00, 18h00 and 21h00) from flowering until veraison. The duration of the watering period was 9 minutes with a flow rate of 2 L h -1 , corresponding to 0.6 L day -1 from budburst to flowering and 1.5 L day -1 from flowering to veraison.

Once plants entered the phenotyping platform (from veraison to physiological ripeness), genotypes and water treatment (mild WD ‘M-WD’ and high WD ‘H-WD’) were randomized in a split-plot design with five blocks. Within each block, genotypes were randomly distributed in the main plot while the water treatment to the subplot. A total of 5 replicates per ‘genotype × water treatment’ were assessed (5 plants × 6 genotypes × 2 water treatment = 60). M-WD and H-WD corresponded to soil moisture capacity (SMC) of 60% and 30% (respectively), which were maintained according to pot weight target values by daily irrigations (up to four times a day 8h00, 13h00, 17h00 and 20h00). For each individual plant, the target weight used for irrigation was calculated as in ( Coupel-Ledru et al., 2014 ) and it was defined based on a pre-experiment using 4 potted plants at the same stage of development and substrate to the plants under study. The pre-experiment consisted of watering the plants to field capacity (FC) and bagging the pots to prevent evaporation from the soil. The plants went on a drying period until permanent wilting point (WP) assessed from predawn water potential (Ψ pd ) measurements. The pots were weighted on each day, at the same time, from FC to WP. The relationship between Ψ pd and soil water content is shown in Supplementary Figure S1 . These values were used as a reference to calculate the SMC ( Equation 1 ).

where Soil TW corresponds to the total pot weight measured daily minus the total tare, Soil W-WP and Soil W-FC to the soil weight at permanent wilting point (2691 g on average) and at field capacity (3064 g on average), both determined during the pre-experiment and applied to all plants. The total tare corresponded to the sum of plant fresh weight (measured by image analysis at veraison, as described below) and the tutor weight (200 g).

2.3 Definition of fruit physiological ripeness stage and cluster biomass

Mean berry weight at veraison was obtained from the berry volume determined from the images (BV VER ), using the parameters of a linear regression fitted at harvest between the measured mean berry weight and the image-based berry volume at harvest (BV HAR ):

The biomass of clusters at veraison was then determined by multiplying the mean berry weight estimated from the pictures taken at veraison by the number of berries per plant counted at harvest.

At the conclusion of the experiment, all plants were weighted to record vegetative fresh biomass (shoots + leaves). The dry biomass of leaves (Leaf DW ) and shoots (Shoot DW ) were assessed after drying all samples for 15 days at 60°C. At this same stage, images of clusters were taken for fitting the relation between mean berry weight and the estimated berry volume (BV HAR ) ( Equation 2 ). The number of clusters, fresh fruit weight (F FW ) and number of berries were directly assessed. Berry weight was determined by dividing the weight of all berries by the total number of berries per plant.

2.4 Total leaf area and canopy biomass

The vegetative biomass, total leaf area of individual plants were estimated through RGB image analysis at the onset of their entry into the platform at veraison (see below) or from direct measurements at the conclusion of the experiment. The images of all plants at veraison were acquired within the PhenoArch platform ( Cabrera-Bosquet et al., 2016 ), hosted at M3P (Montpellier Plant Phenotyping Platforms, https://www6.montpellier.inrae.fr/lepse/Plateformes-de-phenotypage-M3P ). Images were captured for each plant from 13 different angles, which included 12 side views with a 30° rotational difference, as well as one top view.

For vegetative biomass and total leaf area estimations at veraison, plant pixels were separated from the background using a combination of thresholding and random forest algorithms, following the methodology described by ( Brichet et al., 2017 ) and converted into mm 2 by calibrating camera positions using reference objects. Then, total plant leaf area and shoot fresh weight were determined from calibration curves established with multiple linear regression models. These models were constructed based on processed images taken in the 13 directions (grapevine database) against ground truth measurements of leaf area and fresh canopy biomass (excluding biomass of clusters) at different stages. The latter measurements (total leaf area and fresh canopy biomass) were taken at the conclusion of the experiment on plants subjected to M-WD and H-WD treatments.

The total leaf area at the end of the experiment was assessed in one plant for treatment using a planimeter (LI-3100C Area Meter, LiCor Biosciences GmbH, Bad Homburg, Germany), and then estimated for all plants by fitting a linear regression between total leaf area and leaves dry weight (Leaf DW ) ( Equation 3 ).

In order to characterize plant balance, the ratio of total cluster fresh weight to leaf area (kg m -2 ) at harvest was calculated.

2.5 Variation of fruit carbon content during fruit ripening

To evaluate the distribution of carbon in the major metabolites of the grapevine fruit, at physiological ripeness each individual plant was harvested and the juice of all berries was extracted. Soluble sugars (SS = glucose + fructose), tartaric (H2T) and malic (H2M) acids were analyzed by high-performance liquid chromatography (HPLC) and UV detector as described in ( Bigard et al., 2019 ). To estimate the soluble carbon content in fruits at veraison, it was considered a concentration of SS, H2T and H2M, for normal sugar level genotypes (3176N, 3159B, Floreal and Syrah) of 100, 120 and 210 mmol L -1 , respectively, and for sugarless genotypes (G14 and G5), of 83, 96 and 258 mmol L -1 , respectively ( Bigard et al., 2022 ). The carbon equivalent conversion was done for SS, H2T and H2M, using MM of 180, 150, 134 g mol -1 , and number of C of 6, 4 and 4, respectively as in ( Wilhelm de Almeida et al., 2023b ). Thus, the variation of fruit carbon content per plant (varC) during the ripening period was determined as follow ( Equation 4 ):

2.6 Plant transpiration

Total plant transpiration over the ripening period (TR) was obtained from the area under the curve of the individual plant pot weight variations recorded every 15 minutes.

2.7 Gas exchange measurements

All gas exchange measurements were performed on one mature and exposed leaf per plant, using a LI-6800 Portable Photosynthesis System equipped with the Multiphase Flash Fluorometer and Chamber (LI- COR Inc., Lincoln, NE, USA). The environmental parameters in the chamber were settled with flow rate of 600 μmol s-1, photosynthetically active radiation (PAR) of 1500 μmol photons m -2 s -1 , CO 2 of 400 µmol mol-1, VPD of 1.8 kPa, and leaf temperature of 28°C for most measurements. Leaves were systematically acclimated to the chamber setting conditions for 5 minutes prior to the measurement described below.

2.7.1 Net photosynthesis, stomatal conductance and leaf transpiration

The net photosynthesis (An) and stomatal conductance (gs) were measured three to four times after veraison and before physiological ripeness, approximately at 5, 10, 25 and 40 days after veraison (DAV), in 5 to 6 plants per treatment.

2.7.2 Maximum rate for carboxylation and electron transport

The parameters of maximum rate for carboxylation (Vcmax) and maximum electron transport rate (Jmax) were calculated from photosynthesis response curves to varying intercellular CO 2 concentrations. Response curves were assessed at 10 DAV on 5 plants per genotype. Those response curves were assessed with the dynamic assimilation technique, utilizing a continuous CO 2 ramp rate of 160 µmol mol -1 min -1 and measurements recorded at each four seconds ( Saathoff and Welles, 2021 ). The reference and sample infrared gas analyzers (IRGAs) were matched every 20 minutes. The dynamic assimilation technique program consists of a ramp down from 400 to 10 µmol mol -1 of CO 2 , which is followed one minute later by a ramp up from 10 to 1100 µmol mol -1 of CO 2 , at a rate of 160 µmol mol -1 of CO 2 . The data used to fit the photosynthesis response curve consisted of the ramp up phase. The parameters Vcmax and Jmax were estimated from the A-Ci fit from the R package ‘plantecophys’, using the default method of the fitacis () function ( Duursma, 2015 ).

2.7.3 Photosynthesis response to light intensity and chlorophyll fluorescence

Dark respiration (Rd) and photosynthesis response curve to PAR (An-PAR) were performed at 25 DAV on 4 plants per treatment.

To assess Rd, leaves were covered with foil paper and dark acclimated for 12 h prior to gas exchange and chlorophyll fluorescence measurements (Fm and Fo). Modifications on chamber environmental conditions were done regarding flow rate, set to 400 μmol s -1 and PAR set to 0 μmol photons m -2 s -1 .

After assessing the dark-adapted parameters, leaves were acclimated at 1800 μmol photons m -2 s -1 and gas exchange measurements and chlorophyll fluorescence measurements (Fm’, Fo’ and Ft) were taken at three to five minutes intervals at decreasing PAR levels: 1800, 1500, 1200, 900, 700, 600, 500, 400, 300, 200, 100, 50 and 0 μmol photons m -2 s -1 .

Photosynthesis response curve to PAR were then fitted with the non-rectangular hyperbola model as described in ( Villalobos-González et al., 2022 ), using the nls() function and the selfstart package for this model, SSnrh from the nlraa package ( Archontoulis and Miguez, 2015 ). The parameters of maximum photosynthetic rate (Asyn) and apparent quantum yield (Φ CO2 ) were then estimated.

The parameters of photochemical and non-photochemical fluorescence quenching, qN and qP respectively, were estimated for each level of light intensity as described in Villalobos-González et al. (2022) .

2.8 Water use efficiency at the leaf and plant levels

Leaf water use efficiency was calculated as the ratio of An to gs (WUE i ). Plant water use efficiency was calculated as the ratio of the fruit carbon (in major soluble components) variation during ripening in soluble sugars (SS), malic acid (H2M) and tartaric acid (H2T) (varC, Equation 4 ) to total transpired water from veraison to harvest (TR) (WUE PL , Equation 5 ). A normalized WUE (WUEpl_n) was also calculated considering a plant with a plant balance of 1 L of fruit to 1 m 2 of leaf area, in order to buffer the effects of the variations in yield per plant and plant leaf area between the genotypes on WUEpl ( Equation 6 ).

2.9 Statistical analysis

In order to account for the split-plot experimental design, the lmer() function was used to fit mixed effects models, where the fixed effects included blocks and the genotype’s interaction with water treatment, while the interaction of blocks and genotypes were considered as random effects. The average mean values of An, gs and WUEi per water treatment, M-WD and H-WD, corresponded to the average values per plant, when SMC ranged from 0.45 to 0.6 and from 0.15 to 0.3, respectively. The values used for qN and qP were those at 1200 PAR (maximum light intensity inside the platform). Multiple comparisons of means were performed using the emmeans and multcomp package, followed by pairwise comparisons with Bonferroni adjustment, with a significance level set at 0.05. To analyze the leaf and plant WUE relationship, Pearson correlations were assessed. The multivariate analysis (PCA) was conducted using FactoMiner package. In order to explore the contribution of variables to total plant transpiration (TR) and WUE (WUEpl), multiple linear regression was employed. The proportion explained by each variable considered in TR (gs, leaf area, sugar loading duration, varC) and in WUEpl (fruit to leaf ratio, TR, WUEi, varC) was calculated by dividing the sum of square by the total sum of square (η 2 ). All graphical processing and statistical tests were performed using R studio software.

3.1 Soil water content capacity, phenology and plant balance

The targeted SMC among water treatments were stable during the duration of the experiment, varying slightly among genotypes, with the average SMC of M-WD treatments ranging from 0.62 in G14, to 0.51 in G5 ( Table 1 ). The H-WD showed significantly lower SMC values ( ca. -47%), ranging from 0.33 in G14 to 0.27 in Floreal (p.value > 0.05). No interaction between treatments was observed ( Table 1 ).

Table 1 Soil water content capacity (SMC), fruit to leaf ratio (kg m -2 ), carbon gain in fruit solubles solids per plant (varC) and total transpired water per plant, from veraison to harvest, in 5 fungus tolerant genotypes and Syrah under M-WD and H-WD treatments.

Veraison started first in 3176N (DOY 181) and occurred lastly in G14, 19 days later (DOY 200) ( Table 2 ). Sugar loading duration was also extreme for those two genotypes, ranging from 55 days in 3176N under H-WD vs 36 days in G14 under M-WD. Most genotypes showed longer durations (up to 10 days) to reach grape physiological ripeness in H-WD when compared to M-WD plants ( Table 2 ). However, in G14 there were no differences on the sugar loading duration between water treatments, and Syrah was the only genotype with an opposite response, i.e. H-WD plants reached physiological ripeness 6 days earlier than M-WD ( Table 2 ).

Table 2 Day of the year of veraison and physiological ripeness stage and sugar loading duration in 5 fungus tolerant genotypes and Syrah under M-WD and H-WD treatments.

Although the fruit fresh mass of the plants was adjusted at the beginning of the experiment, the remaining variations of total leaf area and yield components (berry number and berry weight) among the genotypes ( Supplementary Table S1 ) led to contrasting plant balances (ratio of fresh fruit weight per unit of leaf area) at harvest ( Table 1 ) between genotypes. The genotypes were divided into three main groups, the first conformed by Syrah and 3176N, displaying the highest number of berries and plant balance, with an average ratio of 0.60 kg m -2 irrespective of the water treatment. The second group was conformed by 3159B, G14 and Floreal, showing a lower number of berries and the lowest ratio of 0.20 kg m -2 on average (irrespective of the water treatment). The third group was conformed by G5, which displayed a similar berry number as the second group, but higher berry weight, thus resulting in intermediate plant balance value of 0.39 kg m -2 ( Table 1 ).

3.2 Carbon gain and water loss at the plant level

3.2.1 total carbon gain as fruit soluble solids and total transpiration per plant.

Variation in C gain (varC), i.e. the variation of the main sugars and organic acids ( Equation 4 ) during ripening, was determined by both genotype and water treatment ( Table 1 ). As observed for the fruit to leaf ratio, the C gain was higher for Syrah and 3176N than for Floreal, G14 and 3159B, with an average of 22.3 g C per plant and 11.0 g C per plant, respectively. G5, on the other hand, resulted in an intermediate value of 19 g C per plant. The varC values of the H-WD plants was 23% lower than that of M-HD, with no main differences between genotypes ( Table 1 ). One exception was 3159B which showed stable varC regardless of water treatment ( Table 1 ). Total plant transpiration during ripening (TR), under M-WD, ranged from 24.6 L in G14 to 33.9 L in 3159B, although their leaf areas were similar ( Table 1 ; SupplementaryTable S1 ). Plants under H-WD treatment transpired 36% less of that observed in M-WD (10 L less, on average, over the ripening period).

3.2.2 Observed and normalized values for plant water use efficiency

The observed WUEpl values ( Figure 1 ) varied according to the fruit to leaf area ratio ( Table 1 ), with the highest being recorded for 3176N and the lowest for 3159B, with values of 1.03 g C L -1 of 0.37 g C L -1 , respectively. In order to account for the phenotypic variations observed in both yield and leaf area per plant ( Supplementary Table S1 ), the WUEpl was normalized by the plant balance (WUEpl_n, see Equation 5 ). This normalization is equivalent to calculating the grams of carbon gained per liter of transpired water for a plant displaying 1 L of fruit and 1 m 2 of leaf area ( Figure 1 ). The WUEpl_n was similar for all the genotypes, with an average value of 2.1 g C L -1 in M-WD, with the exception of G14, which reached a higher value of 2.8 g C L -1 ( Figure 1 ). Although the variations of the fruit to leaf ratio were not significant between the water treatments ( Table 1 ), the plant WUE increased in H-WD compared to M-WD by ca . 46% when normalized (WUEpl_n) vsca . 25% when non normalized (WUEpl) ( Figure 1 ).

Figure 1 Means and standard deviations of observed (WUEpl) and normalized per fruit to leaf ratio (WUEpl_n) plant water use efficiency, from veraison to physiological ripeness in 5 fungus tolerant genotypes and Syrah under M-WD and H-WD treatments. Numbers on top indicate the relative difference (%) (calculated as H-WD - M-WD/M-WD * 100). Different letters indicate significant differences between genotypes averaging both water treatments. ‘G’, ‘Treat’ and ‘G: Treat’ stands for the genotype, water treatment and their interaction effects, respectively. ‘***’ and ‘*’ stands for 0.001, and 0.05 levels of significance and ‘ns’ to no-statistical significance.

3.3 Leaf gas exchange response to water deficit

The average mean values of An, gs and WUEi were compared among genotypes under both M-WD and H-WD treatments ( Figure 2 ). The values corresponded to the average values per plant, when SMCinst ranged from 0.45 to 0.6 and from 0.15 to 0.3, respectively. The WUEi is presented as a representative variable of leaf instantaneous WUE (WUEinst) due to the constant VPD throughout the experiment, which resulted in a high correlation between gs and E.

Figure 2 Means and standard deviations of gs, An (A) and WUEi (B) in 5 fungus tolerant genotypes and Syrah under M-WD and H-WD treatments. Different letters indicate significant differences between genotypes within water treatment. ‘G’, ‘Treat’ and ‘G: Treat’ stands for the genotype, water treatment and their interaction effects, respectively. ‘***’, ‘**’, ‘*’ stands for 0.001, 0.01, 0.05 levels of significance and ‘ns’ to no-statistical significance.

3.3.1 Photosynthesis, stomatal conductance and leaf WUE responses to water deficit

All genotypes reduced the net photosynthesis and stomatal conductance, and increased WUEi from M-WD to H-WD ( Figure 2 ). Differences on gs and An among genotypes were mostly observed under M-WD ( Figure 2A ), while on WUEi differences arose under H-WD ( Figure 2B ).

Under M-WD genotypes exhibited either comparable (3176N, 3159B, G14) or lower (Floreal and G5) gs and An values compared to Syrah (0.298 mol H 2 O m -2 s -1 and 17.5 μmol CO 2 m -2 s -1 , respectively). While under H-WD, all genotypes displayed similar average gs and An values of 0.095 mol H 2 O m -2 s -1 and 8.90 μmol CO 2 m -2 s -1 , respectively (p-value ≥ 0.05) ( Figure 2A ). The highest regulations on gs and An were displayed by 3176N, which showed a decrease of 79% and 60%, respectively when comparing M-WD and H-WD ( Supplementary Table S2 ). Despite G14 showing a similar decrease in gs values, of 62%, it showed a similar reduction in An as that of Syrah, of 37% ( Supplementary Table S2 ).

Consequently, there were consistent WUEi values among genotypes under M-WD conditions (averaging 73 μmol CO 2 mol -1 H 2 O), but variations emerged under H-WD conditions, where those genotypes that showed the highest gs regulations, 3176N and G14, also exhibited the highest values of 96.3 μmol CO 2 mol -1 H 2 O and 132.4 μmol CO 2 mol -1 H 2 O, respectively ( Figure 2B ).

3.3.2 Assessing photosynthesis parameters responses to water deficit

To better understand the limitations on photosynthetic parameters and water use efficiency under increasing drought, we compared the averages of the two water treatments for Φ CO2 , Vcmax, Jmax, qP and qN.

Under M-WD, Vcmax values were either comparable (3176N and G14) or lower (3159B, Floreal and G5) than the values observed for Syrah. Genotypes showed different reduction rates when comparing H-WD to M-WD, where Syrah, 3176N and 3159B reduced Vcmax values of more than 30%, while Floreal, G14 and G5 were not significantly affected ( Figure 3A ). This led to more attenuated genotypic differences under H-WD, with only 3159B showing lower values, of 23.7 μmol CO 2 m -2 s -1 , than those displayed by Syrah, 61.1 μmol CO 2 m -2 s -1 ( Figure 3A ). Differently, Jmax showed similar genotype ranking under both M-WD and H-WD, with genotypes showing values either similar (Floreal and G14) or lower (3176N, 3159B and G5) than Syrah. A general decrease in Jmax values of 16%, regardless of genotype, from M-WD to H-WD was also observed ( Figure 3A ).

Figure 3 Means and standard deviations of Vcmax, Jmax (A) and of phi_CO 2 (ΦCO 2 ), qP and qN (B) in 5 fungus tolerant genotypes and Syrah under M-WD and H-WD treatments. Different letters indicate significant differences between genotypes within water treatment. ‘G’, ‘Treat’ and ‘G: Treat’ stands for the genotype, water treatment and their interaction effects, respectively. ‘***’, ‘**’, ‘*’ stands for 0.001, 0.01, 0.05 levels of significance and ‘ns’ to no-statistical significance. Values of qP and qN presented are at 1200 PAR.

In terms of Φ CO2 and qP, genotypes showed comparable values to Syrah, of 0.046 µmol CO 2 mol -1 and 0.54, respectively, under both water treatments ( Figure 3B ). An exception was observed for Φ CO2 where G5 showed lower values than Syrah, on average 0.039 µmol CO 2 mol -1 (regardless of water treatment). Yet, most genotypes showed similar qN values than those of Syrah, of 0.85 and 0.75 in M-WD and H-WD, respectively. Whereas G14 stood out showing higher qN of 0.83 and 0.89, in M-WD and H-WD, respectively ( Figure 3B ).

3.4 Overall genotype responses to water deficit

A principal component analysis was conducted using the leaf variables (An, gs, WUEi, Vcmax, Jmax, phi (Φ CO2 ), qP and qN) and plant variables [WUEpl, WUEpl_n, fruit to leaf ratio (F_LA), carbon gain in fruits (varC) and plant transpiration (TR)] ( Figure 4 ). The PCA explained 78% of the variation, where the first, second and third dimensions (Dim1, Dim2 and Dim3) accounted for 46.3%, 19.1% and 13.6%, respectively ( Figure 4 ). Dim1 distinctly separated both water treatments. An, gs, and qP were positively correlated with M-WD (right side), and qN, WUEi and WUEpl_n were related to H-WD (left side) ( Figures 4A, C ). Dim2 distinctly separated genotypes and it was mainly represented by WUEpl, and to a lesser extent by fruit to leaf ratio (F_LA), varC, WUEi and TR ( Figure 4A ). Syrah, 3176N and G5 were positively correlated to WUEpl and F_LA, and opposite to G14, 3159B and Floreal ( Figure 4B ). The genotypes classification on Dim2 was conserved at both water treatment levels, indicating similar values of WUEpl and fruit to leaf ratio, regardless of the water treatments ( Figure 4B ).

Figure 4 Principal components analysis in Dim1 and Dim2 (A, B) and in Dim1 and Dim3 (C, D) of genotypes leaf and plant performance under moderate (blue) and high (red) water deficit. Points in bold colors represent the mean by genotype and water treatment.

Dim3 was mainly related to leaf variables of Vcmax, Jmax, phi (Φ CO2 ) and An, and to a lesser extent to the plant variable of WUEpl_n ( Figure 4C ). On the right side (M-WD), Syrah and 3176N were related to high An and gs. While on the left side G14 was related to high WUEpl_n and qN and low phi and TR, while 3159B was related to low Jmax and Vcmax ( Figure 4D ).

3.5 Relationship between leaf and plant water use efficiency

The relationship between the leaf and plant WUE either observed (WUEpl) ( Figure 5A ) or normalized (WUEpl_n) ( Figure 5B ) was evaluated. A low correlation was found when analyzing WUEpl in function of WUEi (corr = 0.28, p.value = 0.04, Figure 5A ).

Figure 5 Linear relationship between leaf water use efficiency (WUEi) and plant WUE observed [WUEpl, (A) ] and normalized per fruit to leaf ratio [WUEpl_n, (B) ] in 5 fungus tolerant genotypes and Syrah, under M-WD (blue) and H-WD (red) treatments. Dotted lines represent the general correlation. WUEi values correspond to the average values of M-WD and H-WD, when SMC ranged from 0.45 to 0.6 and from 0.15 to 0.3, respectively.

After plant WUE was normalized, a positive correlation was observed between WUEi and WUEpl_n, indicating that greater WUEi was associated with a higher WUEpl_n (corr = 0.59, p.value< 0.001, Figure 5B ). However, high differences were observed among the genotypes ( Supplementary Table S3 ). Notably, G14 and 3176N showed the greatest deviation from the other genotypes. When comparing the increase in WUEpl_n between the two, G14 and 3176N showed respectively a higher and lower increase in WUEpl_n as WUEi increased ( Figure 5B ).

4 Discussion

In the present study, the response mechanisms of grapevines to contrasting WD levels imposed during the sugar loading into berry’s phase, was analyzed. The mild and high WD (0.6 and 0.3 of SMC) were chosen to represent common soil conditions faced by growers during the critical period of fruit ripening in many mediterranean regions.

High WD negatively affected most physiological variables related to carbon gain and water loss measured either at the leaf (An, gs) or plant level (TR, C accumulation in fruits), while increasing the leaf and plant WUE (WUEi, WUEpl). Although different signatures on the responses to WD were observed among the genotypes in leaf variables, the variations of fruit-to-leaf ratio also played a key cofactor role in those responses.

4.1 Leaf level regulations of water loss and carbon gain

Despite no differences in gs and An being observed among genotypes under H-WD conditions, G14 and 3176N exhibited the highest WUEi, while Syrah showed the lowest ( Figure 2 ). Such variations were mostly related to a high gs reduction in the former genotypes, and a low reduction in the latter when comparing H-WD to M-WD ( Figure 2 ; Supplementary Table S2 ). This less strict gs control of Syrah when compared to G14 and 3176N could be related to its well-reported near-anisohydric behavior under WD ( Schultz, 2003 ).

A common leaf acclimation to WD is the regulation of gs to limit water loss, which subsequently reduces An rates and lead to increases in WUEi. Indeed, the variation in gs is the primary factor impacting both An and WUEi under WD ( Tomás et al., 2014 ; Bota et al., 2016 ). For that, extensive research has been conducted on grapevine genetic variability in the regulation of gs under drought ( Zufferey et al., 2000 ; Bota et al., 2001 ; Bota et al., 2016 ; Flexas et al., 2010 ; Prieto et al., 2010 ). In the present study, 3176N and Floreal exhibited respectively the highest and lowest gs reductions under H-WD ( Supplementary Table S2 ). The control of stomata is associated with biochemical control, specifically abscisic acid, and hydraulic signaling, involving aquaporin proteins ( Gambetta et al., 2017 ; Hasan et al., 2021 ). All of which might influence the differences in gs regulations between varieties ( Coupel-Ledru et al., 2017 ; Shelden et al., 2017 ). Beyond the regulatory mechanisms influencing gs, the consistently lower gs values observed for 3159B, Floreal, G14, and G5, particularly under M-WD conditions and in comparison to Syrah, may be attributed to differences in stomatal anatomy and density among genotypes. These traits were observed to vary among different rice ( Chen et al., 2020 ; Pitaloka et al., 2022 ), and soybean ( Sakoda et al., 2019 ) varieties. However, environmental conditions can also influence these traits ( Zhang et al., 2012 ). For instance, elevated temperature have been shown to lead to larger stomatas in grapevine ( Sadras et al., 2012 ), while previous studies by Bota et al. (2016) have highlighted substantial genetic variability in gs values even under non-water deficit conditions.

Although this study confirms an important variability in such responses (gs, An, WUEi) among these novel genotypes, when comparing the genotype ranking in field conditions ( Wilhelm de Almeida et al., 2023a ) to the current controlled potted-vines experiment, contrasting results were found. In the preceding research 3159B, G5 and G14 displayed higher An reductions as WD increased, while Floreal and 3176N had similar An regulations to Syrah. The WUEi was similarly discordant, with Syrah and Floreal showing the highest increase in WUEi as WD progressed ( Wilhelm de Almeida et al., 2023a ).

Similar contrasting classifications between field and potted vines experiments were also reported by ( Buesa et al., 2022 ), when studying leaf WUEi of different clones of Vitis vinifera ‘Grenache’ responses to WD. The sensitivity of genotypic gs response to drought changes in response to interactions between the genotypes and the environment, that includes the scion and rootstock pairs, the weather and microclimatic conditions (VPD, temperature, wind and light) and the degree of soil WD ( Martínez-Vilalta and Garcia-Forner, 2017 ; Hochberg et al., 2018 ). The phenotyping platform maintains relatively constant conditions compared to open field conditions, with little variation in air VPD and temperature, low light intensities, and no wind. Additionally, soil conditions are highly contrasted as well, as potted plants are subjected to very dry soils with fluctuating conductivities and rapid wet and dry cycles, imposed by irrigation cycles. It is important to note that plants in the field might be more resilient, due to their higher reserve pool when compared to potted plants. This tight dependency to the plant’s environment can explain the lack of stability in genotype classification between studies performed in greenhouse and open-field.

4.2 Non-stomatal limitation of photosynthesis efficiency under water deficit

To account for the impact of photosynthetic properties on WUEi as WD progressed, we analyzed the biochemical (Vcmax and Jmax) and light-harvesting efficiency (Φ CO2 , qP and qN) factors among genotypes ( Figure 3 ). All parameters decrease under H-WD compared to M-WD, at different levels depending on variables, with exception to qN. At M-WD all genotypes exhibited a rather cohesive grouping when comparing the photosynthetic variables functioning, while at H-WD, a more scattered distribution of genotypes was observed in the PCA. This observed dispersion within lower water availability implies a heightened level of differentiation among genotypes, suggesting that the WD accentuated the inherent disparities between them.

Under H-WD the biochemical parameters Vcmax and Jmax both exhibited reductions of 17% and 16%, respectively (regardless of genotype). This observation aligns with their typical correlation, as high levels of carboxylation often require elevated reductive power ( Manter and Kerrigan, 2004 ; Walker et al., 2014 ). The high decrease of Vcmax and Jmax under H-WD in 3159B suggests that plants may have modulated their carboxylation rate, potentially reducing enzyme activity when its substrate, i.e. CO 2 is less available. In a previous study ( Bota et al., 2004 ) it was observed that the content or activity of RuBP was reduced under high WD, after a 50% reduction in An.

It is important to note that in G14, G5, and Floreal, the biochemical process Vcmax was not negatively affected by H-WD, despite the fact that the two former genotypes displayed higher or similar reductions in gs and An compared to Syrah. This lack of effect could be attributed to the lower An when compared to those observed by Bota et al. (2004) , but it could also be indicative of adaptive mechanisms in LSB genotypes that enable them to maintain Vcmax even under H-WD conditions. In the case of G14, this may have resulted in higher An and/or WUEi levels under H-WD when compared to Syrah. Nevertheless, other factors, such as a reduction in mesophyll conductance under WD ( Tomás et al., 2014 ; Perdomo et al., 2017 ; Urban et al., 2017 ), may also contribute to a reduction in CO 2 availability in chloroplasts ( Galmés et al., 2011 ), resulting in a decrease in both Vcmax and Jmax.

Thermal dissipation is an important photoprotective mechanism activated in plants under environmental stress ( Malnoë, 2018 ). Indeed, a negative relationship between gs and qN among genotypes was observed in the PCA ( Figure 4 ), indicating that all genotypes increased heat dissipation under H-WD. Interestingly, G14 displayed a higher qN but similar qP than Syrah, suggesting a higher capacity in dissipating excess energy in the form of heat while maintaining a comparable maintenance of light conversion into chemical energy. Another photoprotective strategy adopted by C3 plants involves photorespiration ( Kozaki and Takeba, 1996 ; Guan et al., 2004 ; Villalobos-González et al., 2022 ), which was proposed to be especially noticeable in genotypes with high sensitivity of stomatal regulation (near-isohydric behavior) ( Villalobos-González et al., 2022 ). This might suggest that 3176N, with the highest regulation of gs but low qN, may have relied more on photorespiration.

Notably, the highest Φ CO2 observed for 3176N ( Figure 3B ) could be an interesting trait to enhance An under WD and low light conditions. This is particularly relevant in complex canopies such as in grapevines, where leaves are often shaded (in denser canopies) or subjected to intraday variations of light environments (in less-dense canopies) ( Escalona et al., 2003 ; Prieto et al., 2012 ). Investigating the rapidity of gs responses would be a crucial point to better understand the contribution of this trait on C gain and WUEi under fluctuating light ( Qu et al., 2016 ; Faralli et al., 2019 ).

4.3 Leaf and whole plant feedbacks under water deficit

In spite of crop load management among plants at the onset of the experiment, the fruit-to-leaf ratio was 3-folds higher in the present study for Syrah and 3176N compared to all other genotypes, regardless of the water treatments, while LSB genotypes showed either similar (G5) or lower (G14) ratios when compared to Syrah. Variations in fruit-to-leaf ratio were mostly related to variations in total leaf area ( Supplementary Table S1 ). The higher ratio for Syrah and 3176N was a result of low leaf area associated to high yield. The high yield for these genotypes might be a result of genetic expression, as these two genotypes were also characterized as highly productive in field phenotyping experiments ( Wilhelm de Almeida et al., 2023a ). Genetic variability within grapevine yield formation was previously observed in regards to bunch number per shoot ( Grzeskowiak et al., 2013 ), number of inflorescence per flower and in fruit set rate ( Ibáñez et al., 2019 ).

Ultimately, a high influence of the fruit-to-leaf ratio on C accumulation was observed, where genotypes with higher ratios also showed a higher carbon gain in fruits ( Figures 4A, B ). As the ratio was consistently below 1 kg m -2 across all genotypes and water treatments, no trophic impediment in fruit maturation is expected. This can be due to a proper balance between sink and source activities ( Kliewer and Dokoozlian, 2005 ), or yet due to the fact that as the sink force was very low for some genotypes, the expected source limitation due to WD was not enough to impair sugar accumulation ( Intrigliolo and Castel, 2011 ). However, the longer sugar loading for H-WD compared to M-WD reflected an insufficient C gain in fruits. The fruit-to-leaf ratio not only influenced the C accumulation in fruits and WUEpl, but also An rates. For instance, the two genotypes with the highest fruit-to-leaf ratio, Syrah and 3176N, also exhibited the highest An rates. This could be attributed to a feedback response from sink (fruits) to source (leaf) organs. Feedback mechanisms between sink (crop load) and source activities (An rates) within the plant system have been reported in many fruit crops including apple ( Pallas et al., 2018 ), peach ( Wang et al., 2022 ) and grapevine ( Rossouw et al., 2017 ; Martínez-Lüscher and Kurtural, 2021 ; Faralli et al., 2022 ). Conversely, plants of G5, despite having a similar fruit-to-leaf ratio to Syrah, did not exhibit increased An rates. This discrepancy might be associated with its LSB trait, indicating a lower carbon demand in the fruits, thereby influencing the assimilate allocation despite comparable ratios. Furthermore, plant balance was demonstrated to alter C reserves and mobilization in grapevines, further emphasizing its intricate and pivotal role in plant performance ( Holzapfel and Smith, 2012 ; Hernández-Montes et al., 2022 ).

It is important to notice that when normalizing fruit-to-leaf ratio among genotypes, the levelling process aligns all plants based on those with lower productivity or vegetative expression. Consequently, this approach might suggest a skewed sense of comfort, favoring highly productive or vegetative genotypes like 3176N and 3159B (respectively) over inherently less fertile or vegetative ones such as Floreal and G5 (respectively). This also raises questions when considering genotypes inherently characterized by lower sugar demands in fruits, such as the LSB genotypes G14 and G5 ( Bigard et al., 2022 ). When studying fleshy fruits of genotypes that decouple water and sugar demands, the definition of yield per se presents a direct challenge. Yield can be defined as fresh weight, which is mainly related to water demand, or as biomass, which is mostly linked to C demand. From a physiological perspective, this implies that genotypes should be normalized based on either water or C demand. If we consider yield in terms of fresh weight, i.e. in relation to the volume of fruit and therefore water, these genotypes that require less C, would theoretically be less reliant on photosynthesis during the sugar loading period. This suggests that they may exhibit lower photosynthetic rates. However, the photosynthetic rate did not appear to be particularly lower in the LSB genotypes. In addition, previous studies have proposed a relationship between high photosynthetic activity and C export to roots ( Escalona et al., 2012 ; Hernández-Montes et al., 2022 ). This might imply that the G14 and G5 genotypes would have more C available to allocate to other plant sinks, such as reserves. A genotype-dependent response in C allocation to the root system was previously observed when comparing Tempranillo and Grenache under WD conditions, which was mainly accounted by their differences in C respiratory losses ( Hernández-Montes et al., 2022 ). These characteristics could imply a superior performance of these LSB genotypes in facing WD conditions.

The total transpired water from veraison to harvest also varied among the genotypes and water treatments, due, at least partly to the fluctuations of total leaf area and of the duration of sugar loading ( Supplementary Figure S2 ). Under M-WD, the high transpiration observed for 3159B was backed up by the highest total leaf area ( Supplementary Table S1 ) and sugar loading durations (48 days) ( Table 2 ). Syrah, which showed similar high transpiration, also showed the longest ripening period (50 days) although displaying one of the lowest total leaf areas. In contrast, G14 exhibited high vegetative development, but had one of the lowest transpiration rates due to its short sugar loading duration (36 days). Under H-WD, total transpired water per plant was reduced by ca. -36% compared to M-WD, in spite of a longer ripening duration for all genotypes except Syrah (up to 10 days). The reduction of transpiration is a recognized water conservation strategy in plants and it is ultimately linked to leaf area and gs regulations ( Simonneau et al., 2017 ), indeed gs and TR were closely related in the PCA ( Figure 4A ). In the present study, total leaf area and gs were reduced under H-WD by about respectively 15% and 57%. Such low reduction of leaf area can be explained by the late onset of WD treatments (starting at veraison).

Although other factors such as boundary layer conductance, leaf cuticular conductance, stomatal density and size were shown to influence plant transpiration, of various plant species, including poplar ( Grünhofer et al., 2022 ), grapevines ( Konlechner and Sauer, 2016 ), rice ( Chen et al., 2020 ; Pitaloka et al., 2022 ), and soybeans ( Sakoda et al., 2019 ), it is likely that these variables accounted for variations between genotypes rather than differences arising from water treatments. Indeed, the boundary layer conductance was conserved between treatments inside the platform, due to its rather constant and controlled environmental conditions. In addition, the effects of drought on these traits are commonly established during early stages of leaf development ( Bi et al., 2017 ; Bertolino et al., 2019 ), a period when all plants in our study experienced uniform, optimal conditions of light, water, and nutrients.

As the C accumulation in fruits was less reduced than plant transpiration under H-WD, WUEpl was promoted for all genotypes. However, the differences of WUEpl among the genotypes mainly resulted from the variations in the fruit-to-leaf ratio ( Supplementary Figure S3 ). Yet, when normalized the WUEpl_n most genotypes showed comparable values to Syrah, despite showing lower plant transpiration. One exception was observed for the genotype G14 which showed the highest WUEpl_n ( Figure 1 ). This suggests that under water-limiting situations, all fungi-tolerant genotypes tended to regulate their water loss over the ripening period more efficiently than Syrah, but G14 clearly stood out with a higher WUE. Furthermore, a lack of consideration for critical variables, including plant respiration and night transpiration, when assessing WUEi may contribute to observed discrepancies ( Escalona et al., 2012 ; Medrano et al., 2015b ; Coupel-Ledru et al., 2016 ). Such factors represent significant sources of carbon and water loss at the plant level. Studies have estimated that fruit carbon respiration alone accounts for approximately 18% of total leaf assimilated carbon ( Hernández-Montes et al., 2022 ). Similarly, night transpiration can contribute up to 30% of daily water loss, particularly under dry conditions ( Coupel-Ledru et al., 2016 ), with both factors demonstrating variability among grapevine genotypes. It is important to acknowledge that despite the normalization process allowing for a balanced comparison between genotypes at similar fruit-to-leaf ratios, i.e. considering a plant with 1 L of fruit and 1 m² of leaf area, it may introduce bias by assuming linearity in genotypic responses regardless of variations in the crop load. In addition, it do not considering the variations in C demand in genotypes presenting the LSB trait.

5 Conclusions

Physiological and biochemical responses of gas exchange related parameters varied depending on the genotype, highlighting the intricate relationship between genotypic traits and environmental conditions.

The fruit-to-leaf ratio emerged as a key determinant influencing C accumulation in fruits and WUEpl. Genotypes with higher fruit-to-leaf ratios demonstrated higher C gains in fruits and An rates, highlighting the role of sink-source interactions. Despite differences in responses under varying WD conditions, WUEpl was promoted for all genotypes due to reduced plant transpiration, with the LSB genotype, G14, exhibiting the highest normalized WUEpl.

When compared to Syrah, most genotypes displayed either equal or superior WUE at leaf and plant level. Two genotypes should be highlighted, 3176N and G14 due to their higher WUEi and different regulations in Φ CO2 in the former and in Vcmax and qN in the latter. Furthermore, the genotype-dependent correlation between leaf-level and whole-plant WUE emphasizes the need to further explore the significance of factors such as fruit-to-leaf ratio, canopy and root structure, plant respiration, and night transpiration in influencing overall WUE.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Author contributions

LW: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Software, Validation, Visualization, Writing – original draft, Writing – review & editing. CP: Conceptualization, Methodology, Resources, Supervision, Visualization, Writing – review & editing. HO: Conceptualization, Funding acquisition, Supervision, Writing – review & editing. LT: Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing. AP: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The study was funded by the Occitanie Region, the Conseil Interprofessionnel des Vins du Languedoc - CIVL, the International Organization of Vine and Wine - OIV, INRAE and Institut Agro Montpellier (France).

Acknowledgments

The authors thank Stéphane Berthézène and Romain Boulord for their essential technical support and management of experiments, the students Riccardo Rossi and Louis Haegi for their support in data acquisition, Ménanie Veyret and Centina Pinier for metabolites analysis, Llorenç Cabrera-Bosquet, Aude Coupel-Ledru and Thierry Simonneau for scientific advices.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpls.2024.1405343/full#supplementary-material

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Keywords: chlorophyll fluorescence, stomatal conductance, whole-plant transpiration, berry sugarless trait, grapevine

Citation: Wilhelm de Almeida L, Pastenes C, Ojeda H, Torregrosa L and Pellegrino A (2024) Water deficit differentially modulates leaf photosynthesis and transpiration of fungus-tolerant Muscadinia x Vitis hybrids. Front. Plant Sci. 15:1405343. doi: 10.3389/fpls.2024.1405343

Received: 22 March 2024; Accepted: 30 April 2024; Published: 16 May 2024.

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Copyright © 2024 Wilhelm de Almeida, Pastenes, Ojeda, Torregrosa and Pellegrino. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Anne Pellegrino, [email protected]

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