Vitamin E

Tocochromanols are a small group of natural products synthesized exclusively by photosynthetic organisms and include the tocopherols and tocotrienols that are vitamin E, an essential lipid-soluble antioxidant in the human diet. The major source of vitamin E in the human diet is plant-derived products, which can vary by orders of magnitude in tocochromanol content and composition and hence vitamin E activity. In the past decade, tremendous progress has been made in our understanding of the molecular genetics of tocochromanol synthesis in plants and cyanobacteria, and all the biosynthetic genes of the core pathway have now been cloned and studied in detail. Significant progress has been made in engineering tocochromanol content and composition in plant tissues. Our understanding of tocochromanol function(s) during the plant life cycle has been advanced by the isolation and study of pathway mutants that accumulate specific intermediates or completely eliminate tocochromanols from the organism. Tocochromanols are absolutely essential for limiting lipid oxidation during seed desiccation, storage and germination, and the severe fitness impact of tocochromanol deficiency at this stage of the plant life cycle makes it obvious why tocochromanol synthesis has been conserved in all seed-bearing plants during evolution. However, the functions of tocochromanols in mature plant tissues are surprisingly more limited than had long been assumed, especially in regard with plant stress.