Alpha-Tocopherol-Induced Regulation of Growth and Metabolism in Plants Under Non-stress and Stress Conditions

Alpha-tocopherol (α-Toc) is a member of the vitamin E family and is lipid soluble. Its biosynthesis is by the reaction of isopentyl diphosphate and homogentisic acid in plastid membranes. The putative biochemical activities of tocopherols are linked with the formation of tocopherol quinone species, which subsequently undergo degradation and recycling within cells/tissues. α-Toc plays a key role in a variety of plant metabolic processes throughout the ontogeny of plants. It can maintain the integrity and fluidity of photosynthesizing membranes. It can also neutralize lipid peroxy radicals, consequently blocking lipid peroxidation by quenching oxidative cations. It preserves membrane integrity by retaining membranous structural components under environmental constraints such as water deficiency, high salt content, toxic metals, high/low temperatures, and radiations. α-Toc also induces cellular signalling pathways within biological membranes. Its biosynthesis varies during growth and developmental stages as well as under different environmental conditions. The current review primarily focuses on how α-Toc can regulate various metabolic processes involved in promoting plant growth and development under stress and non-stress and how it can effectively counteract the stress-induced high accumulation of reactive oxygen species (ROS). Currently, exogenous application of α-Toc has been widely reported as a potential means of promoting resistance in plants to a variety of stressful environments.