Functions of tocopherols in the cells of plants and other photosynthetic organisms

Abstract

Tocopherol synthesis has only been observed in photosynthetic organisms (plants, algae and some cy-anobacteria). Tocopherol is synthesized in the inner membrane of chloroplasts and distributed between chlo-roplast membranes, thylakoids and plastoglobules. Physiological significance of tocopherols for human and animal is well-studied, but relatively little is known about their function in plant organisms. Among the best characterized functions of tocopherols in cells is their ability to scavenge and quench reactive oxygen species and fat-soluble by-products of oxidative stress. There are the data on the participation of different mechanisms of α-tocopherol action in protecting photosystem II (PS II) from photoinhibition both by deactivation of singlet oxygen produced by PS II and by reduction of proton permeability of thylakoid membranes, leading to acidification of lumen under high light conditions and activation ofviolaxanthin de-epoxidase. Additional biological activity of tocopherols, independent of its antioxidant functions have been demonstrated. Basic mechanisms for these effects are connected with the modulation of signal transduction pathways by specific tocopherols and, in some instances, by transcriptional activation of gene expression.