Biological Role of Ascorbate in Plants

Ascorbate, as a strong and active antioxidant, plays an important role in keeping human health. It helps promote iron absorption, increase antibody concentration and improve human immunity. Ascorbate is used to regenerate a-tocopherol (vitamin E), and remove radicals which could induce cancer and senescence. Ascorbate is beneficial to strengthen blood vessel and decrease cholesterol concentration. Ascorbate can help prevent arteriosclerosis related cardiovascular diseases as well as hypertension and apoplexy. Ascorbate prevents disease associated with connective tissue (e.g., scurvy), promotes the formation of collagen and development of cartilage, strengthens tooth, tightens skin and facilitates wound healing [1]. In contrast to most animals, humans lack the ability to synthesize ascorbate as a result of a mutation in the last enzyme required for ascorbate biosynthesis. Human must absorb ascorbate from dietary sources, especially plant products such as fresh fruit and vegetable [2]. Consistent with its multi-function in human and animals, ascorbate in plants has beneficial influences on various aspects in plants. Through modifying gene expression, ascorbate not only act to regulate defense and survival but also act via phytohormones to modulate plant growth [3]. Emerging research results indicate that ascorbate, existing widely in plants as the abundant micromolecule substance, fulfils its essential roles in series of physiological processes such as plant defense against oxidization, co-factor of key enzymes, plant cell division, cell expansion, growth and development, and senescence [4–6]. Ascorbate, at least in some plant species, is also the substrate for the biosynthesis of oxalate and tartrate [7, 8]. However, the multifunction of ascorbate makes it complicated to decipher its exact role under certain physiological process. Arabidopsis thaliana mutants lacking ascorbate cannot grow well, but it is not known which function is critical: control of reactive oxygen or the proposed roles in modulating cell expansion and division [9]. Thus, there is need to increase our understanding of this enigmatic molecule since it could be involved in a wide range of important functions from