Roles of the bundle sheath cells in leaves of C₃ plants

This review considers aspects of the structure and functions of the parenchymatous bundle sheath that surrounds the veins in the leaves of many C₃ plants. It includes a discussion of bundle sheath structure and its related structures (bundle sheath extensions and the paraveinal mesophyll), its relationship to the mestome sheath in some grasses, and its chloroplast content. Its metabolic roles in photosynthesis, carbohydrate synthesis and storage, the import and export of nitrogen and sulphur, and the metabolism of reactive oxygen species are discussed and are compared with the role of the bundle sheath in leaves of C₄ plants. Its role as an interface between the vasculature and the mesophyll is considered in relation to the movement of water and assimilates during leaf development, export of photosynthates, and senescence.