Question

Describe the C₄ Cycle or Hatch & Slack Pathway.

Answer 1

• Discovered by Hatch & Slack, so called as Hatch &Slack Pathway. 
• First stable product is 4- carbon compound (Oxaloacetic Acid) hence called C₄-cycle and plants having this cycle are called as C₄ plants. 
• C₄ plants have special kind of leaf anatomy called as “Kranz anatomy”.
• (Presence of two types of photosynthetic cells, i.e. mesophyll cells and bundle sheaths cells). 
• In C₄ plants (Maize, sugar cane etc.) both C₃ cycle (In bundle sheath cell chloroplasts) & C₄ cycle (In mesophyll cell chloroplasts) occurs. 

C₄ plants have special type of leaf anatomy, they tolerate higher temperatures. In this pathway, oxaloacetic acid (OAA) is the first stable product formed. It is 4 carbon atoms compound, hence called C₄ pathway (Hatch and Slack Cycle). 

The leaf has two types of cells : mesophyll cells and Bundle sheath cells (Kranz anatomy). Initially CO₂ is taken up by phosphoenol pyruvate (PEP) in mesophyll cells and changed to oxaloacetic acid (OAA) in the presence of PEP carboxylase. Oxaloacetate is reduced to maltate/asparate that reach into bundle sheath cells.