Photorespiration

photorespiration

1. University of Salahaddin College of Education Biology department Photorespiration 1 Halala Rahman Qadir M.Sc. Plant physiology 11/14/2015

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3. The objectives are: Definition of photorespiration 3 What happens during the process called "photorespiration"? Photorespiration in plants 11/14/2015

4. Definition of photorespiration Photorespiration: (also known as the  oxidative photosynthetic carbon cycle , or  C2 photosynthesis ) is a process in  plant metabolism  which attempts to reduce the consequences of a wasteful oxygenation reaction by the  enzyme  RuBisCO . Or the process that leads to only one 3PGA being produced in the dark reaction in chloroplasts 11/14/2015 4

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6. Photorespiration in plants The end result is that photorespiration decreases the net amount of carbon dioxide which is converted into  sugars  by a photosynthesizing plant. By interfering with photosynthesis in this way, photorespiration may significantly limit the growth rate of some plants. 11/14/2015 6

7. 9/12/07 7 Photorespiration depends on light “wastes” CO 2 protects against light damage favored by high O 2 , low CO 2 and warm temperatures

8. What happens during the process called "photorespiration"? It has long intrigued biologists that O 2   has an inhibitory effect upon photosynthesis . As shown in the following hypothetical experiment, in the presence of elevated O 2  levels, photosynthesis rates are lower . 11/14/2015 8

9. It is now known that this response to oxygen is due to competition between O 2  and CO 2  on the Rubisco enzyme of the Calvin-Benson cycle . You will recall that in the "normal" reaction, CO 2   is joined with RUBP to form 2 molecules of 3PGA . 11/14/2015 9

10. 11/14/2015 10 In the process called   photorespiration , O 2  replaces CO 2  in a non-productive, wasteful reaction.

11. It is believed that photorespiration in plants has increased over geologic time and is the result of increasing levels of O 2  in the atmosphere--the byproduct of photosynthetic organisms themselves. The appearance of C4-type plants appears to be an evolutionary mechanism by which photorespiration is suppressed. 11/14/2015 11

12. It has long been the dream of biologists to increase the production of certain crop plants, such as wheat , that carry on C3-type photosynthesis by genetically re-engineer them to perform  C4-type photosynthesis . It seems unlikely that this goal will be accomplished in the near future due to the complex anatomical and metabolic differences that exist between C3- and C4-type plants. 11/14/2015 12