**Daniel R. Gallie**

Department of Biochemistry, University of California, Riverside, CA 92521-0129, USA; E-Mail: drgallie@citrus.ucr.edu; Tel.: +1-951-827-7298; Fax: +1-951-827-4434.

*Received: 19 July 2013; in revised form: 16 August 2013 / Accepted: 21 August 2013 / Published: 30 August 2013* 

**Abstract:** Vitamin C serves as a cofactor in the synthesis of collagen needed to support cardiovascular function, maintenance of cartilage, bones, and teeth, as well as being required in wound healing. Although vitamin C is essential, humans are one of the few mammalian species unable to synthesize the vitamin and must obtain it through dietary sources. Only low levels of the vitamin are required to prevent scurvy but subclinical vitamin C deficiency can cause less obvious symptoms such as cardiovascular impairment. Up to a third of the adult population in the U.S. obtains less than the recommended amount of vitamin C from dietary sources of which plant-based foods constitute the major source. Consequently, strategies to increase vitamin C content in plants have been developed over the last decade and include increasing its synthesis as well as its recycling, *i.e.*, the reduction of the oxidized form of ascorbic acid that is produced in reactions back into its reduced form. Increasing vitamin C levels in plants, however, is not without consequences. This review provides an overview of the approaches used to increase vitamin C content in plants and the successes achieved. Also discussed are some of the potential limitations of increasing vitamin C and how these may be overcome.

**Keywords:** L-ascorbic acid; ascorbate; photosynthesis; DHAR; MDAR; reactive oxygen species
