(a) : C4 pathway was first reported in members of family Gramineae (grasses) like sugarcane, maize, sorghum, etc. In C4 plants PEPCo (PEP carboxylase) is the key enzyme used to fix CO2 in C4 plants. Oxaloacetic acid is a 4 -C compound and is the first stable product so this pathway is known as C4 cycle.