Biosynthesis and Regulation of Ascorbic Acid in Plants

Ascorbate is the most abundant water-soluble redox compound in plants and has multiple functions as a redox buffer. There is compelling genetic evidence that the biosynthesis of ascorbate proceeds via the d-mannose/l-galactose pathway and is the most significant source of ascorbate in plants. Alternative pathways, including those via d-galacturonate and d-glucuronate, have been proposed but there is no convincing genetic evidence. In order to carry out its physiological functions, cellular ascorbate contents need to be tightly controlled in response to various environmental conditions. In this chapter, we will describe the recent progression on the metabolic process of ascorbate biosynthesis and its regulation.