What structural differences are there in leaves of C4 plants?

C4 plants have a unique leaf structure with specialised Kranz anatomy and bundle sheath cells.

C4 plants, unlike their C3 counterparts, have evolved a unique leaf structure to optimise photosynthesis under conditions of high light intensity, high temperatures, and dryness. This structural adaptation is known as Kranz anatomy, which is German for 'wreath' or 'ring', referring to the arrangement of cells in the leaf.

In the leaves of C4 plants, photosynthetic cells are organised into two distinct types: mesophyll cells and bundle sheath cells. The mesophyll cells are located around the leaf's veins, while the bundle sheath cells form a ring around the vascular bundles. This arrangement creates a dual system for carbon fixation, which is the process of converting carbon dioxide into organic compounds during photosynthesis.

The mesophyll cells are the site of the initial carbon fixation. They contain the enzyme PEP carboxylase, which has a high affinity for carbon dioxide and can fix it even when its concentration is low. The product of this reaction is a four-carbon compound (hence the name C4), which is then transported to the bundle sheath cells.

The bundle sheath cells are the site of the Calvin cycle, the second stage of photosynthesis. They are characterised by large chloroplasts, thick walls, and few intercellular spaces. These features help to create a microenvironment with a high concentration of carbon dioxide, which is beneficial for the Calvin cycle. The thick walls of the bundle sheath cells also prevent the leakage of carbon dioxide, further enhancing the efficiency of photosynthesis.

In summary, the structural differences in the leaves of C4 plants, particularly the presence of Kranz anatomy and bundle sheath cells, enable them to perform photosynthesis more efficiently under certain environmental conditions. This is a fascinating example of how plants have adapted to their environment at a cellular level.