Mesofyll

Mesofyll, commonly referred to as mesophyll in English, is the internal tissue of a leaf located between the upper and lower epidermis. It is the primary site of photosynthesis and gas exchange within the leaf and is typically organized into two distinct layers: the palisade mesophyll and the spongy mesophyll.

The palisade mesophyll consists of elongated chlorenchyma cells just below the upper epidermis, densely packed with chloroplasts to maximize light capture. The spongy mesophyll lies beneath the palisade layer and is composed of loosely arranged cells with extensive intercellular air spaces that facilitate diffusion of carbon dioxide, oxygen, and water vapor toward and from the stomata.

The mesophyll is richly vascularized by xylem and phloem within the leaf veins and is bounded by a protective epidermis bearing stomata on the lower surface. Photosynthesis in the mesophyll uses light absorbed by chloroplasts to convert carbon dioxide and water into sugars, which are then transported through the phloem.

Variation and adaptations: In leaves adapted to low light, the palisade layer may be reduced or composed of smaller cells; in xerophytic or succulent plants, the mesophyll may be compressed or otherwise modified to reduce water loss. In C4 and CAM plants, mesophyll cells participate in initial CO2 fixation or the storage and transfer of carbon compounds in coordination with other cell types, aiding CO2 concentration and water-use efficiency.