Increasing vitamin C content of plants through enhanced ascorbate recycling

doi:10.1073/pnas.0635176100

Increasing vitamin C content of plants through enhanced ascorbate recycling

Department of Biochemistry, University of California, Riverside, CA 92521

Edited by Roger N. Beachy, Donald Danforth Plant Science Center, St. Louis, MO, and approved January 22, 2003 (received for review August 26, 2002)

Abstract

Vitamin C (ascorbic acid) is essential to prevent disease associated with connective tissue (e.g., scurvy), improves cardiovascular and immune cell functions, and is used to regenerate α-tocopherol (vitamin E). In contrast to most animals, humans lack the ability to synthesize ascorbic acid as a result of a mutation in the last enzyme required for ascorbate biosynthesis. Vitamin C, therefore, must be obtained from dietary sources and, because it cannot be stored in the body, it must be obtained regularly. Once used, ascorbic acid can be regenerated from its oxidized form in a reaction catalyzed by dehydroascorbate reductase (DHAR). To examine whether overexpression of DHAR in plants would increase the level of ascorbic acid through improved ascorbate recycling, a DHAR cDNA from wheat was isolated and expressed in tobacco and maize, where DHAR expression was increased up to 32- and 100-fold, respectively. The increase in DHAR expression increased foliar and kernel ascorbic acid levels 2- to 4-fold and significantly increased the ascorbate redox state in both tobacco and maize. In addition, the level of glutathione, the reductant used by DHAR, also increased, as did its redox state. These results demonstrate that the vitamin C content of plants can be elevated by increasing expression of the enzyme responsible for recycling ascorbate.

ascorbic acid‖dehydroascorbate reductase‖redox state‖ glutathione‖nutrition

Footnotes

↵ * To whom correspondence should be addressed. E-mail: drgallie{at}citrus.ucr.edu.
This paper was submitted directly (Track II) to the PNAS office.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database [accession nos. AY074784 (wheat DHAR), AY074786 (rice DHAR), AY074787 (tobacco DHAR), and AY074785 (Arabidopsis DHAR)].
Abbreviations:

AsA,

ascorbic acid;

MDHA,

monodehydroascorbate;

MDHAR,

MDHA reductase;

DHA,

dehydroascorbate;

DHAR,

DHA reductase;

GSH,

reduced glutathione;

GSSG,

oxidized glutathione;

GR,

glutathione reductase;

APX,

ascorbate peroxidase;

GLDH,

l-galactono-1,4-lactone dehydrogenase;

SOD,

superoxide dismutase;

CAT,

catalase;

FW,

fresh weight