Question

The first carbon dioxide acceptor in $C_4$ plant is

• A. Phosphoenolpyruvate.
• B. Oxaloacetic acid.
• C. Phosphoglyceric acid.
• D. Ribulose 1, 5- diphosphate.

Answer 1

The correct option is A Phosphoenolpyruvate.

The $C_4$ plants are called so because the first stable product of this process are the four carbon atom containing organic acids like oxalo-acetic acid and malic acid. The initial acceptor of carbon dioxide is phosphoenol pyruvic acid (PEP) and the initial carboxylating enzyme is PEP carboxylase. The initial carboxylation reaction occurs in the mesophyll cells. In the $C_4$ organic acids are decarboxylated in the bundle sheath cells to release carbon dioxide. In the bundle sheath cells the carbon dioxide is fixed with the help of RuBisCO enzyme.