What is photorespiration ? Explain the mechanism and its significance.
Photorespiration
is a process which involves loss of fixed carbon as CO2 in plants in the
presence of light. It is initiated in chloroplasts. This process does not
produce ATP or NADPH and is a wasteful process.
Photorespiration occurs usually
when there is the high concentration of oxygen. Under such circumstances,
RuBisCO, the enzyme that catalyses the carboxylation of RuBP during the first
step of Calvin cycle, functions as an oxygenase. Some O2 does bind to
RuBisCO and hence CO2 fixation is decreased. The RuBP binds with
O2 to form one molecule of PGA (3C compound) and phosphoglycolate (2C
compound ) in the pathway of photorespiration. There is neither the synthesis
sugar nor of ATP. Rather, it results in the release of CO2 with the
utilisation of ATP. It leads to a 25 percent loss of the fixed CO2.
Significance of photorespiration:
- Photorespiration helps in dissipation of
energy where stomata get closed during daytime because of water stress.
- Photorespiration
protects the plant from photoxidative damage by dissipating excess of
excitation energy.