Decker and Tio (1959) reported that light induces oxidation of photosynthetic intermediates with the help of oxygen in tobacco. It is called as photorespiration. The photorespiration is defined by Krotkov (1963) as an extra input of O2 and extra release of CO2 by green plants is light.
Photorespiration is the uptake of O2 and release of CO2 in light and results from the biosynthesis of glycolate in chloroplasts and subsequent metabolism of glycolate acid in the same leaf cell. Biochemical mechanism for photorespiration is also called glycolate metabolism. Loss of energy occurs during this process. The process of photorespiration involves the involvement of chloroplasts, peroxisomes and mitochondria. RuBP carboxylase also catalyses another reaction which interferes with the successful functioning of Calvin cycle.
The process of photorespiration interferes with the successful functioning of Calvin cycle. Photorespiration is quite different from respiration as no ATP or NADH are produced. Moreover, the process is harmful to plants because as much as half the photosynthetically fixed carbon dioxide (in the form of RuBP) may be lost into the atmosphere through this process.
Any increase in O2 concentration would favour the uptake of O2 rather than CO2 and thus, inhibit photosynthesis for this rubisco functions as RuBP oxygenase. Photorespiration is closely related to CO2 compensation point and occurs only in those plants which have high CO2 compensation point such as C3 plants.
It is absent in plants which have very low CO2 compensation point such as maize, sugarcane (C4 plants). Photorespiration generally occurs in temperate plants. Few photorespiring plants are : Rice, bean, wheat, barley, rice etc. Inhibitors of glycolic acid oxidase such as hydroxy sulphonates inhibit the process of photorespiration. Unlike usual mitochondria respiration neither reduced coenzymes are generated in photorespiration nor the oxidation of glycolate is coupled with the formation of ATP molecules. Photorespiration (C2 cycle) is enhanced by bright light, high temperature, high oxygen and low CO2 concentration.
CO2 compensation point : In photosynthesis, CO2 is utilized in presence of light to release O2 whereas in respiration, O2 is taken and CO2 is released. If light factor is saturating, there will be certain CO2 concentration at which rate of photosynthesis is just equal to rate of respiration or photosynthesis just compensates respiration or apparent photosynthesis is nil. It is called CO2 compensation point. Rate of photosynthesis is higher than that of respiration during day time and ratio of O2 produced to that consumed is 10 : 1.
CO2 compensation point is very low in C-4 plants, i.e., 0 to 5 ppm whereas high CO2 compensation point is found in C-3 plants, i.e. 25 to 100 ppm.
During compensation point there is no evolution of any gas.
Decker and Tio (1959) reported that light induces oxidation of photosynthetic intermediates with the help of oxygen in tobacco. It is called as photorespiration. The photorespiration is defined by Krotkov (1963) as an extra input of O2 and extra release of CO2 by green plants is light.
Photorespiration is the uptake of O2 and release of CO2 in light and results from the biosynthesis of glycolate in chloroplasts and subsequent metabolism of glycolate acid in the same leaf cell. Biochemical mechanism for photorespiration is also called glycolate metabolism. Loss of energy occurs during this process. The process of photorespiration involves the involvement of chloroplasts, peroxisomes and mitochondria. RuBP carboxylase also catalyses another reaction which interferes with the successful functioning of Calvin cycle.
The process of photorespiration interferes with the successful functioning of Calvin cycle. Photorespiration is quite different from respiration as no ATP or NADH are produced. Moreover, the process is harmful to plants because as much as half the photosynthetically fixed carbon dioxide (in the form of RuBP) may be lost into the atmosphere through this process.
Any increase in O2 concentration would favour the uptake of O2 rather than CO2 and thus, inhibit photosynthesis for this rubisco functions as RuBP oxygenase. Photorespiration is closely related to CO2 compensation point and occurs only in those plants which have high CO2 compensation point such as C3 plants.
It is absent in plants which have very low CO2 compensation point such as maize, sugarcane (C4 plants). Photorespiration generally occurs in temperate plants. Few photorespiring plants are : Rice, bean, wheat, barley, rice etc. Inhibitors of glycolic acid oxidase such as hydroxy sulphonates inhibit the process of photorespiration. Unlike usual mitochondria respiration neither reduced coenzymes are generated in photorespiration nor the oxidation of glycolate is coupled with the formation of ATP molecules. Photorespiration (C2 cycle) is enhanced by bright light, high temperature, high oxygen and low CO2 concentration.
CO2 compensation point : In photosynthesis, CO2 is utilized in presence of light to release O2 whereas in respiration, O2 is taken and CO2 is released. If light factor is saturating, there will be certain CO2 concentration at which rate of photosynthesis is just equal to rate of respiration or photosynthesis just compensates respiration or apparent photosynthesis is nil. It is called CO2 compensation point. Rate of photosynthesis is higher than that of respiration during day time and ratio of O2 produced to that consumed is 10 : 1.
CO2 compensation point is very low in C-4 plants, i.e., 0 to 5 ppm whereas high CO2 compensation point is found in C-3 plants, i.e. 25 to 100 ppm.
During compensation point there is no evolution of any gas.