Photorespiration (C2 Pathway) in Plants.

Photorespiration PPT will help the introduction, process, explanation with research proof.

1. Photorespiration Jasmine Juliet Teaching Assistant Biochemistry, AC&RI, Madurai.

2. Photorespiration (C2 Cycle) Photorespiration is the light-dependent evolution of CO 2 . The photorespiratory pathway is initiated by the fixation of O 2  by Rubisco producing phosphoglycolate , which is metabolized in the photorespiratory pathway to form CO 2  and NH 3 .

3. Photorespiration (C2 Cycle) photorespiration appears to be a very wasteful process in which net CO 2   fixation is reduced and energy is also used up in the process. Any factor that reduces the availability of CO 2  or increases the availability of O 2  to rubisco will increase the levels of photorespiration .

4. Photorespiration (C2 Cycle) The reactions of photorespiration cycle occur in three organelles: C hloroplasts, P eroxisomes , and Mitochondria. ( i ) (a) The C2 cycle is initiated in the chloroplast with the formation of 2-phosphoglycolate , which is subsequently converted to glycolate and Pi by the action of phosphoglycolate phosphatase . ( i ) (b) The glycolate exits the chloroplast and enters into the peroxisome .

5. P hotorespiration (C2 C ycle) (ii) The glycolate reacts with O 2 to produce glyoxylate and H 2 O 2 which is catalysed by glycolate oxidase . (iii) Two molecules of glyoxylate are aminated to form glycine in a reaction catalysed by glutamate:glyoxylate aminotransferase . H 2 O 2 is removed by the abundant catalase present in peroxisomes to H 2 O and O 2 .

6. Photorespiration (C2 Cycle) (iv) The glycine produced in the peroxisome moves into the mitochondria. For every two molecules of glycine, one molecule of serine, CO 2 and NH 3 is produced, and one NAD + is reduced to NADH. This takes place through the action of glycine decarboxylase complex. One CO 2 is produced for every two molecules of O 2 taken up by the action of RuBP oxygenase .

7. Photorespiration (C2 Cycle) (v) The serine produced in the mitochondria now moves into the peroxisome , where it is deaminated to hydroxypyruvate by serine:glyoxylate aminotransferase . Then, hydroxypyruvate is reduced to glycerate by hydroxypyruvate reductase . (vi) The glycerate exits the peroxisome and enters the chloroplast and is phosphorylated by glycerate kinase to 3-phosphoglycerate . This reaction completes the conversion of two molecules of phosphoglycolate to one of 3-PGA, which can now enter the C3 cycle.

8. Benefits of Photorespiration Photorespiration have some beneficial role in plants: P hoto-protective effects (preventing light-induced damage to the molecules involved in photosynthesis), Maintains redox balance in cells Support plant immune defenses  .

9. Research article evidences The protective role of photorespiration may be especially important under stress conditions such as drought when leaf stomata’s close in the light in order to prevent excess water loss  ( Wingler et al., 1999 ). Lowering photorespiration may not result in increased growth rates for plants. Photorespiration may be necessary for the assimilation of nitrate from soil. Thus, a lowering in photorespiration by genetic engineering or because of increasing atmospheric carbon dioxide may not benefit plants as has been proposed. Several physiological processes may be responsible for linking photorespiration and nitrogen assimilation . Reference: Rachmilevitch S, Cousins AB, Bloom AJ (August 2004). "Nitrate assimilation in plant shoots depends on photorespiration". Proceedings of the National Academy of Sciences of the United States of America.  101  (31): 11506–10. 

10. Thank You