The photorespiratory losses are checked by certain grasses by having physiological adaptation. The process of photosynthesis occurs in mesophyll cells and bundle sheath cells.
Mesophyll cells : (a) Initially, CO2 is taken up by phosphoenol pyruvate (3C) and changed to oxaloacetate (4C) in the presence of PEP carboxylase, (b) Oxaloacetate is reduced to Malate/Aspartate, the product formed, reach into bundle sheath.
Bundle sheath : (a) The oxidation of Malate (and Aspartate) occurs with release of carbon dioxide and formation of Pyruvate (3C).
(b) Due to the increased CO2 concentration, the Rubisco functions as carboxylase and not as oxygenase.
(c) The photosynthetic losses are prevented.
(d) RuBP operates now under Calvin cycle and
Pyruvate transported back to mesophyll cells is changed into phosphoenol-pyruvate, to keep the cycle going.