Photorespiration is a type of respiration which occurs in green cells in presence of light. It involves three organelles - chloroplast, peroxisomes and mitochondria. Respiratory substrate in photorespiration is a 2-carbon compound glycolic acid (2C), hence called C, cycle. RuBP-carboxylase in normal O/CO conc, acts as 'carboxylase'. It is the key enzyme of photosynthesis in C plants.
Photorespiration is a wasteful process in plants in which plants intake oxygen, and sunlight and release carbon dioxide and no glucose is formed. Photorespiration generally takes place when the concentration of oxygen in the leaves is very high and that of carbon dioxide is very low.
In Calvin cycle carbon dioxide fixation does not take place . Hence, instead of carbon dioxide oxygen reacts with RuBP.
Photorespiration in C3 and C4 Plants:
C4 plants do not undergo photorespiration due to their special mechanism to increase the CO2 level for enzyme binding.
In Hatch and Slack Pathway, C4 acid and oxaloacetic acid breaks down to release CO2.
This ensures a high concentration of intercellular CO2.
Thus, in C4 plants, RuBisCO is more active as a carboxylase enzyme rather than as an oxygenase.
