ABSTRACT
High concentrations of L-ascorbic acid are characteristic of plant tissues. Ascorbate is one of the most important vitamins in the human diet, being obtained largely from vegetables, fruit, and other plant material. Green leaves may contain as much ascorbate as chlorophyll. The presence of such a remarkable amount of ascorbate may suggest considerable metabolic significance, particularly if the amount is related to biological importance. Glutathione peroxidase, which is important in H2O2 detoxification in animals is largely absent from plant tissues. Seasonal variations in the ascorbate content of leaves have been found; on the whole, the ascorbate pool in chloroplasts and leaves is maintained at a remarkably constant level. Oxidation of ascorbic acid occurs in two sequential steps, forming, in the first instance, monodehydroascorbate, and subsequently dehydroascorbate. The monodehydroascorbate radical spontaneously disproportionates to ascorbate and dehydroascorbate. The conversion of glucosone and sorbosone to ascorbic acid has been observed in bean and spinach leaves.
