Increasing vitamin C content of plants through enhanced ascorbate recycling

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 ␣-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

Transgenic potato overexpressing Arabidopsis cytosolic AtDHAR1 showed higher tolerance to herbicide, drought and salt stresses

“…cytosolic DHAR in reducing oxidized DHA that has diffused from the apoplast, chloroplasts, and other cell compartments into the cytosol. A similar increase in AsA due to increased expression of DHAR was reported by Chen et al (2003) and Eltayeb et al (2006). Our results confirmed that efficient recycling of AsA to increase its reduced pool could be achieved via overproduction of DHAR.…”

Allelic Variation in Paralogs of GDP-l-Galactose Phosphorylase Is a Major Determinant of Vitamin C Concentrations in Apple Fruit

“…1). Indeed, overexpression of an Arabidopsis (Arabidopsis thaliana) MDHAR (Eltayeb et al, 2007) and a wheat (Triticum aestivum) DHAR (Chen et al, 2003) have both been shown to increase foliar AsA concentrations in tobacco (Nicotiana tabacum). MDHAR activity has also been positively correlated with both AsA and fruit firmness in tomato (Solanum lycopersicum) after chilling stress (Stevens et al, 2008).…”

Multigene families encode the major enzymes of antioxidant metabolism in Eucalyptus grandis L

“…DHAR catalyzes the reduction of dehydroascorbate to ascorbate, using glutathione as reducing substrate (Figure 1). Cytosolic DHAR encoding cDNAs from wheat, rice, tomato, and arabidopsis, and chloroplastic cDNAs from spinach were previously described (Chen et al, 2003;Shimaoka et al, 2000). We have identified three Eucalyptus clusters encoding DHAR isoforms, but two of them do not represent full-length transcripts.…”