Introduction
Krotkov (1963) was the first to notice that some plants released CO2 in response to light. This was only observed in green cells. He coined the term “photorespiration” to describe the phenomenon.
Photorespiration: Definition
Photorespiration is the emission of carbon dioxide during respiration in the presence of light. Beta, Phaseolus, Gossypium, Pisum, Capsicum, Petunia, Antirrhinum, Helianthus, Oryza, and Nitella and Chlorella algae are examples. Further research has found that photorespiration is linked to high temperatures ranging from 25 to 350 degrees Celsius and high oxygen levels in the environment. The rise in O2 causes a steady increase in photorespiration.
Mechanism of Photorespiration
Only after Bowes, Ogren, and Hageman’s study could a detailed mechanism of photorespiration be discovered (1971). They discovered that the enzyme Ribulose 1, 5-biphosphate carboxylase (Rubisco) is involved in both lower and higher CO2 concentrations. Rubisco has carboxylase activity when CO2 levels are normal, but when O2 levels are high or the O2/CO2 ratio is high, Rubisco has oxygenase activity and catalyzes the addition of O2 to RuBP to form a molecule of phosphoglycolic acid and a molecule of phosphoglyceric acid.
Photosynthesis is linked to photorespiration. As a result, the chloroplast is one of the organelles where photorespiration occurs. The presence of glycolate metabolism enzymes in peroxisomes and the discovery of peroxisomes (in close connection with chloroplasts) in plants suggests that peroxisomes are another location of photorespiration. Glycolate oxidase, glutamate-glyoxylate transaminase, and catalase enzymes have been discovered in peroxisomes. Peroxisomes may not be the true location of CO2 evolution during photorespiration, according to Tolbert and Kisaki (1969), but they may carry out part of the reaction to generate a substrate for CO2 evolution. Tolbert (1971) proposed that CO2 evolution in photorespiration occurs in mitochondria. Photorespiration is thought to be mediated by three organelles: chloroplasts, peroxisomes, and mitochondria, according to experimental findings. Using labeled carbon in tobacco leaves, researchers discovered that the first carbon atom of a two-carbon molecule, glycolate, is released as CO2. Glycol’s carboxyl group (COOH) is assumed to be the CO2 donor during photorespiratory release. The effects of light on CO2 emission are abolished by loss of chlorophyll from leaves due to nutritional deprivation or mutation. It isn’t present in cells that aren’t chlorophyllous or photosynthesizing.
Photorespiration’s Importance:
1. Photorespiration is only seen in plants that have a dark reaction as part of their Calvin cycle (C3 plants), but it is absent in C4 plants, according to research.
2. Photorespiration is found in temperate plants, whereas tropical plants do not.
3. There is no evidence of ATP production in the reaction pathway. Because this system occurs in low CO2 conditions, it is thought that this mechanism was frequent during earlier evolutionary times when CO2 levels in the atmosphere were very low and that it has been inhibited as CO2 levels in the atmosphere have increased.
4. Plant photosynthetic efficiency is reduced when the photorespiration mechanism is present. Genetists are working hard to create C3 plant strains with low photorespiration rates. Because this process is superfluous and non-essential in plants, such efforts are being made.
5. Scientists, on the other hand, believe that photorespiration serves as a protective and supporting function that lowers oxygen harm to chloroplasts. By absorbing O2, the mechanism aids in the maintenance of a low oxidative state in C3 plant chloroplasts. Oxygen-free radicals are harmful and can harm organelles, whereas photorespiration keeps oxygen-free radicals away.
Dark respiration versus Photorespiration
1. It is found in every living cell on the planet.
2. Carbohydrates may be used as a respiratory substrate.
3. The procedure is carried out in the cytoplasm.
4. The substrate could be old or brand new.
5. ATP molecules are created during this process.
6. There is no production of H2O2.
7. It can be found in both C3 and C4 plants.
8. The transamination reaction does not occur.
9. Only a small amount of O2 is required for the process to work.
10. NAD is broken down into NADH2.
11. It is light-independent and can be found in both dark and light environments.
Photorespiration
1. It’s found in green photosynthetic cells. It’s found in plants that use the Calvin cycle to repair CO2.
2. The substrate is glycolate, which can be either fat or protein.
3. It is found between the chloroplast, peroxisome mitochondria, cytosol, and mitochondria.
4. The substrate is always new.
5. There are no ATP molecules produced.
6. H2O2 is created as a result of the procedure.
7. It can be found in C3 plants.
8. A transamination reaction occurs.
9. It has a modest positive connection with O2 Concentration.
10. In this case, NADH2 is oxidized.
11. It is a light-dependent process that takes both day and night. only put it in the light
Role of the RUBISCO in Photorespiration
RUBISCO developed roughly 3 billion years ago, most likely from enzymes involved in sulfur metabolism but it is still the enzyme responsible for the great majority of net CO2 fixation from the environment today. The only source of molecular oxygen in the atmosphere at the time of RUBISCO development was presumably photolysis of water by UV light, and concentrations were 10-14 below current levels. At the same time, CO2 levels were at least 100 times higher than they are now. Due to the lack of evolutionary pressure, the first RUBISCO enzymes were likely terrible at distinguishing CO2 from O2. Huge volumes of CO2 were fixed into biomass with the advent of oxygenic photosynthesis in cyanobacteria, which partially sedimented and did not return to the global carbon cycle. Water was utilized as the reductant for the photosynthetic electron transport chain, which resulted in equimolar levels of O2 being discharged into the atmosphere.
Top Questions
Question: Name some plants which show PhotoRespiration?
ANS: Photorespiration is the emission of carbon dioxide during respiration in the presence of light. Beta, Phaseolus, Gossypium, Pisum, Capsicum, Petunia, Antirrhinum, Helianthus, Oryza, Nitella, and Chlorella algae are examples.
Question: What causes PhotoRespiration?
ANS: Photorespiration is linked to high temperatures ranging from 25 to 350 degrees Celsius and high oxygen levels in the environment. The rise in O2 causes a steady increase in photorespiration.
Question: Who first observed the PhotoRespiration?
ANS: Krotkov (1963) was the first to notice that some plants released CO2 in response to light. This was only observed in green cells. He coined the term “Photorespiration” to describe the Phenomenon.