For carboxylation reaction in C4 plants which amongst the following enzymes is/are involved:(a) RuBisCO(b) PEPcase(c) Pyruvate orthophosphate dikinase(d) Ribulose-5-phosphate kinase.

The primary CO2 acceptor in C4 cycle is a 3-carbon molecule phosphoenol pyruvate (PEP) and is present in the mesophyll cells. The enzyme responsible for this fixation is PEP carboxylase or PEPcase. It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells itself, which are transported to bundle sheath cells. In bundle sheath cells these C4 acids are broken down to release CO2 and 3-carbon molecule (pyruvic acid). The CO2 released in the bundle sheath cells enters the C3 or the Calvin cycle. In the Calvin cycle again carboxylation occurs with the help of the enzyme RuBiSCO.