C4 pathway is an adaptation to tolerate strong light, high temperature ; high quantity of oxygen etc. Evolution of C4 plants from C3 plants can be described as follows :
1. C3 plants undergo photorespiration in strong light or at high temperature which is a wasteful process in which no energy is produced.
2. In C3 plants RUBP carboxylase get denatured in strong light, but in C4 plants it does not.
3. These C4 plants have Kranz anatomy. In this case mesophyll cells have grana thylakoid and bundle sheath cells have agranal thylakoids present in stroma of chloroplast.
4. In C4 plant, light reaction occurs in mesophyll cells and RuBisCo is found in bundle sheath cells in which CO2 fixation occurs. Thus, in C4 plants RuBisCo remains protected from sunlight and is also protected from oxygenation, because in bundle sheeth cells only dark reaction occurs.
Thus, to avoid photorespiration, oxygenation of RuBisCo etc. C4 plants were evolved from C3plants. The C4 plants are maize, sugar cane, grasses etc.
What is photosystem ? Which is the pigment that acts as reaction centre ? Describe the interaction of photosystem I and photosystem II.
