In the Hatch-Slack pathway, the C₄ acid formed in the mesophyll cells is transported to the bundle sheath cells. What is the immediate primary metabolic event that this C₄ acid undergoes upon entering the bundle sheath cells?

Step-by-step solution

In the C₄ pathway (Hatch-Slack pathway), the C₄ acid (such as malic acid or aspartic acid) formed in the mesophyll cells is transported to the bundle sheath cells. Upon entering the bundle sheath cells, these C₄ acids undergo decarboxylation. They are broken down to release CO₂ and a 3-carbon molecule. The released CO₂ then enters the Calvin cycle ( C₃ pathway) catalyzed by RuBisCO, while the 3-carbon molecule is transported back to the mesophyll to regenerate PEP. Answer: Decarboxylation