Process of Photorespiration

Ribulose-1,5-bisphosphate-carboxylase/oxygenase (RUBISCO) is the enzyme that initiates photorespiration in almost all photosynthetic organisms. RUBISCO is also the enzyme that is responsible for CO2 fixation in virtually all photosynthetic organisms. In the photorespiratory pathway, the phosphoglycolate formed by oxygen fixation is recycled to the Calvin cycle intermediate phosphoglycerate, which is then recycled again. During this reaction cascade, energy and reducing equivalents are consumed, and a portion of the previously fixed carbon is released as CO2. Consequently, photorespiration was often regarded as a wasteful process by many people. In this paper, we present an overview of the current knowledge about the components of the photorespiratory pathway, which has been gained primarily through genetic and biochemical studies in Arabidopsis plants. 

The energy costs of photorespiration are calculated based on this knowledge, but the numerous positive aspects of photorespiration that call into question the traditional view of photorespiration as a wasteful pathway are also discussed. An outline of possible alternative pathways that could be used in addition to the primary pathway is provided. Recently published research on photorespiration in photosynthetic organisms that express a carbon concentrating mechanism, as well as the implications of these findings for understanding Arabidopsis photorespiration, are reviewed and discussed. Finally, approaches to metabolic engineering that aim to increase plant productivity by reducing photorespiratory losses are discussed and evaluated.

Photorespiration occurs when the concentration of carbon dioxide within a leaf decreases. This occurs primarily on hot, arid days when plants are forced to close their stomata to prevent excessive water loss from transpiration. Keeping the plants’ stomata closed while they try to fix carbon dioxide will result in them consuming all of the carbon dioxides they have stored and the oxygen proportions of the leaf increasing when compared to the carbon dioxide levels in the surrounding environment.

What is Photorespiration?

A living organism’s photorespiration is the chemical reactions that take place within it that result in the production of phosphoglycolate during oxygenation, which is catalysed by the enzyme RubisCO. Photorespiration inhibits photosynthesis by interfering with CO2 fixation by RubisCO.

Increasing the temperature and the intensity of the light influences photorespiration by accelerating the formation of glycolate and the flow of oxygen and nutrients through the photorespiratory pathway.

Photorespiration is characterised by the light-dependent acceptance of oxygen and the discharge of carbon dioxide, and it is associated with the formation and metabolism of a minute particle known as glycolate.

Photosynthesis and photorespiration are two biological processes (in flourishing plants) that can operate simultaneously beside each other because photosynthesis produces oxygen as a byproduct and photorespiration produce carbon dioxide as a byproduct, and the aforementioned gases are the raw materials for the processes above. 

Photosynthesis produces oxygen as a byproduct and photorespiration produces carbon dioxide as a byproduct, and the aforementioned gases are the raw materials for the processes above. When the carbon dioxide levels inside the leaf drop to approximately 50 parts per million (ppm), RuBisCO begins combining oxygen with RuBP as a substitute for carbon dioxide in the leaf.

As a result, rather than manufacturing two molecules of 3C-PGA units, only one unit of PGA is fashioned with a toxic 2C molecule known as phosphoglycolate, as an alternative to manufacturing two molecules of 3C-PGA units.

The plant goes through a series of steps to rid itself of the phosphoglycolate. First and foremost, it immediately purges itself from the phosphate cluster by converting the units of phosphate into glycolic acid. Following that, the glycolic acid is transferred to the peroxisome, where it is transformed into glycine and other compounds. The mitochondria of the plant cell are responsible for the conversion of glycine to serine. The serine produced as a result of this process is used to construct other organic units. Carbon dioxide is released from the vegetation due to these reactions, which charge the plants’ energy reserves.

Photosynthesis in C4 plants

Plants that reproduce in warm, arid climates, such as sugarcane and corn, have evolved a carbon dioxide fixation system that is distinct from that of these crops. The structure of the leaves of these plants differs from the structure of a normal leaf in several ways. They are well-known for exhibiting Kranz’s anatomy. Bundle sheath cells, which are dense-walled parenchyma cells that surround the phloem and xylem of these leaves and are responsible for the majority of photosynthesis, surround the phloem and xylem of these leaves.

Photorespiration in C4 Plants

Any amount of O2 binds to RuBisCO in C3 plants, reducing the amount of CO2 fixation.

In this case, the RuBP binds to O2 instead of being converted into two PGA molecules, resulting in the formation of one phosphoglycerate and one phosphoglycolate molecule through a process known as Photorespiration.

This pathway does not involve the synthesis of sugars or energy-producing ATP molecules. Instead, it aids in the release of CO2 through the use of ATP.

In the photorespiratory pathway, there is no synthesis of either ATP or NADPH. Consequently, photo-respiration is an expensive procedure.

CAM – Crassulacean Acid Metabolism

 Except for the fact that they take carbon dioxide during the night and convert it to malic or aspartic acid, this section of flora follows the same procedure as the C4 section. The vacuoles of their photosynthetic cells serve as a storage space for these compounds. As soon as the sun shines, these plants close their stomata and disintegrate the malic acid to maintain a carbon dioxide ratio high enough to prevent photorespiration from occurring. This allows the stomata of the leaves to be closed to prevent withering from occurring. Kranz’s anatomy is not displayed in this section of the flora.

Conclusion:

RuBisCO is the enzyme that is found in the greatest quantity all over the world. Its active location can bind to both CO2 and oxygen. The enzyme that will bind to the enzyme is determined by the relative concentrations of oxygen and carbon dioxide. As carbon dioxide concentrations rise, photorespiration occurs, which is defined as a decrease in the rate of photosynthesis as a result of the increase.