In C4 plants, in which type of cells does the Calvin cycle occur?

In C4 plants, the Calvin cycle occurs in bundle sheath cells. These cells surround the leaf’s vascular bundles and contain chloroplasts where carbon dioxide is concentrated around the enzyme RuBisCO.

C4 photosynthesis divides carbon processing between two cell types. Mesophyll cells first use PEP carboxylase to attach carbon dioxide to a three-carbon compound, forming a four-carbon molecule such as malate or aspartate. That molecule moves into the bundle sheath cells, where it releases carbon dioxide. RuBisCO then uses the concentrated carbon dioxide in the Calvin cycle to produce carbohydrates.

This arrangement is often associated with Kranz anatomy, in which vascular bundles are encircled by bundle sheath cells and then by mesophyll cells. It helps C4 plants reduce photorespiration, a wasteful process that becomes more likely when temperatures are high or carbon dioxide is scarce.

Maize, sugarcane, and many warm-climate grasses use C4 photosynthesis. The mesophyll cells therefore perform the initial carbon-fixation step, but the Calvin cycle itself is conventionally identified with the bundle sheath cells.