C4 plants are plants that are better adapted to dry tropical regions, and they exhibit an additional C4 pathway, in addition to the Calvin cycle. It was confirmed by Hatch and Slack in 1966.
It is found in many monocots like sugarcane, maize, sorghum, Cyperus, etc. and some dicots like Amaranthus, Euphorbia, etc.
C4 plants have characteristic Kranz anatomy in their leaves. In C4 leaves, the vascular bundles are surrounded by large parenchymatous cells called bundle sheath cells that are further surrounded by mesophyll cells.
In C4 leaves, there are morphologically two distinct types of chloroplasts called dimorphic chloroplasts.
Bundle sheath chloroplasts- larger in size, without grana (Agranal chloroplast), but containing starch grains.
Mesophyll chloroplasts- smaller in size, with grana, but lack starch grains.
In C4 plants, atmospheric CO2 is primarily accepted by phosphoenolpyruvate (PEP) present in mesophyll chloroplasts, in the presence of PEP Carboxylase enzyme leading to the formation of oxaloacetic acid (a 4C compound). As the first stable product of CO2 fixation is a 4-carbon compound; hence, it is known as the C4 cycle.