Question

Even though a very few cells in a C4 plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Let’s discuss why?

Answer 1

Part 1: Anatomy of C4 plants
The arrangement of mesophyll and bundle sheath cells in the leaf of C4 plants is different from C3 plants. The parenchymatous cell which is a type of ground tissue present in the leaf are called mesophyll cells. The cells surrounding the vascular bundles is called the bundle sheath cells. In C4 plant these mesophyll cells are clustered around the bundle sheath cells and forms a shape which is similar to the wreath. This arrangement seen in the leaf of C4 plants is called Kranz anatomy.

Part 2: Significance of Kranz anatomy
The atmospheric $C{O}_2$ is fixed initially in the mesophyll cells. Malate formed in this process is transported to the bundle sheath cells where it is converted into $C{O}_2$ . The enzyme RuBisCO is present within the bundle sheath cells. When the concentration of oxygen is high it can act as an oxygenase. This results in photorespiration. But in C4 plants the loss of energy molecules due to photorespiration is reduced as the concentration of $C{O}_2$ is high in the bundle sheath cells. Thus RuBisCO acts as a carboxylase and the Calvin cycle in C4 plants occurs within the bundle sheath cells. Therefore even though there are very few cells that perform Calvin cycle in C4 plants, the productivity is high as there is no loss of energy molecules due to photorespiration.