Improving the nutritional value of crops through enhancement of L-ascorbic acid (vitamin C) content: rationale and biotechnological opportunities.

L-Ascorbic acid (AsA, vitamin C) is an essential human nutrient that must be obtained in the diet, with the vast majority being obtained from plant foods. A vitamin C-deficient diet results in the onset of scurvy, which can have lethal consequences. However, vitamin C has also been implicated in the prevention of chronic diseases such as heart disease, stroke, cancer, and several neurodegenerative diseases. Although the supporting evidence for these claims is disputed, the dietary allowances for vitamin C have been recently increased in several countries, including the United States. This scenario, together with the general perception by consumers of vitamin C as being of benefit in the prevention of several lifestyle diseases and associated with general "well-being", contributes to a market rationale for enhancing the vitamin C content of crops. In recent years, there has been substantial progress in the understanding of vitamin C biochemistry in plants with a number of structural genes cloned. Here these findings are reviewed, and a description of how such knowledge could be applied to the nutritional enhancement of crops is given.