Photorespiration

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Photorespiration

Description

Photorespiration is the process by which the enzyme RuBisCo oxygenates the Ribulose Biphosphate (RuBP) instead of carboxylating it as part of the Calvin-Benson cycle, creating phosphoglycolate, a product that cannot be used within this cycle, and thus wasting the energy produced by photosynthesis (in the form of a direct cost in ATP and NAD(P)H). It is estimated that approximately 25 % of RuBisCo reactions are photorespiration, meaning a potential 25 % reduction in photosynthetic output due to the carbon fixed by photorespiration being released as carbon dioxide and nitrogen as ammonia, while the other product, 3-phosphoglycerate (G3P), requires a higher metabolic cost. This process involves a complex network of enzyme and metabolite exchanges between the chloroplasts, peroxisomes and mitochondria. It is also known as the oxidative photosynthetic carbon cycle or C2 photosynthesis and abiotic conditions tend to affect it, such as temperature and the atmospheric partial pressures of oxygen and carbon dioxide. Certain type of plants (C4 plants and CAM plants) and algae have biochemical and biophysical mechanisms to overcome the photosynthetic losses due to photorespiration making them more photosynthetically efficient than C3 plants. Recent plant biotechnology advances have been focused on increasing plant photosynthetic carbon fixation by reducing photorespiration loses.


Reference:

Stern K 2003. Introductory Plant Biology New York: McGraw-Hill. ISBN 978-0-07-290941-8.
Photorespiration.png
Simplified photorespiration diagram
Communicated by Huete-Ortega M 2020-07-29
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