Even though a very few cells in a `C_(4)` plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?

Explanation

H.P. Kortschak and C.E Hartt found that in sugarcane the first products of photosynthesis were acids containing 4 - c atoms, rather than the 3c - acid. The same has been found true for many tropical plants. Ex : Maize, Elensine, Sorghum, Amaranthus & Euphorbia etc. These plants are called `C_(4)` plants. Hatch and Slack explained the manner of `CO_(2)` fixation and reduction in such plants.
The leaves of `C_(4)` plants show Kranz anatomy, means `wreath. there vascular bundles are surrounded by two rings of cells. (i) Bundle sheath cells (ii) Mesophyll cells.
1. In `C_(4)` - pathway, the primary acceptor of `CO_(2)` is phosphoenol pyruvic acid (PEP) and which is converted into oxaloacetate in the presence of enzyme PEP carboxylase.
2. The oxaloacetate is converted into malate or aspartate depending upon the species.
3. The malate formed in mesophyll cells is transferred to the neighbour bundle sheath cells via plasmodesmata between these cells.
4. In the bundle sheath cell the malate is now decarboxylated producing pyruvate and `CO_(2)` by action of NADP specific malic enzyme.
5. In the bundle sheath cells the `CO_(2)` arising from the decarboxylation of malate is now fixed again in exactly the same calvin pathway of `C_(3)` plants.
6. Sucrose & starch are ultemately formed from 3 PGA in bundle sheath cells.
7. The pyruvate formed by decarboxylation of malate in the bundle sheath is transported bock to the mesophyll cells where it is converted into phosphoenol pyruvate by the action of enzyme pyruvate phosphate dikinase.