photorespiration

1. University of Salahaddin
College of Education
Biology department
1
Halala Rahman Qadir
M.Sc. Plant physiology
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3. The objectives are:
Definition of photorespiration
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What happens during the process
called "photorespiration"?
Photorespiration in plants
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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
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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.
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Photorespiration
• depends on light
• “wastes” CO2
• protects against light
damage
• favored by high O2, low
CO2 and warm
temperatures

8. What happens during the process called "photorespiration"?
• It has long intrigued biologists that O2 has an
inhibitory effect upon photosynthesis. As shown
in the following hypothetical experiment, in the
presence of elevated O2 levels, photosynthesis
rates are lower.
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9. It is now known that this response to oxygen is due
to competition between O2 and CO2 on the
Rubisco enzyme of the Calvin-Benson cycle. You
will recall that in the "normal" reaction, CO2 is
joined with RUBP to form 2 molecules of 3PGA.
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In the process called photorespiration, O2 replaces
CO2 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 O2 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.
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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.
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