Question

Calvin cycle of $C_4$ plants operates in the

• A. Grana of mesophyll chloroplasts.
• B. Stroma of chloroplasts in mesophyll cells.
• C. Bundle sheath cells of chloroplasts.
• D. None of the above.

Answer 1

The correct option is C Bundle sheath cells of chloroplasts.

Kranz anatomy is a characteristic of $C_4$ plants like Atriplex, Sugarcane, Maize. $C_4$ plants are better photosynthesizers than $C_3$ plants, as they do not show photorespiration. These plants have a special ring of thick walled bundle sheath cells around vascular bundle. The bundle sheath cells lack intercellular spaces. They have large chloroplasts without grana. In the bundle sheath cells carbon dioxide is fixed by the enzyme RuBisCO. After carbon dioxide fixation by RuBisCO, Calvin cycle proceeds as in $C_3$ plants. The mesophyll cells are the usual cell type as found in $C_3$ plants also. Initial carbon dioxide fixation into organic acids occurs in the mesophyll cells. These organic acids are transported to bundle sheath cells through plasmodesmata. In bundle sheath cells they are decarboxylated to release carbon dioxide, which is fixed using RuBisCO and normal Calvin cycle takes place.