Mechanism of C4-cycle:

• There are two carboxylation reaction takes place in C4-cycle. First carboxylation
• reaction takes place in mesophyll chloroplast and second carboxylation takes place in bundle sheath cells in the following step wise reaction:

Pathways of Hatch and Slack Cycle

1. The 4-carbon acid transported from mesophyll cells may be malate as above, or may be aspartate.

2. The 3-carbon acid transported back from bundle-sheath cells may be pyruvate, or alanine.

3. The enzyme which catalyses decarboxylation in bundle-sheath cells differs. In maize and sugarcane, the enzyme is NADP-malic enzyme, in millet, it is NAD-malic enzyme, and in Panicum maximum it is PEP carboxykinase.