Enhanced Ascorbic Acid Accumulation through Overexpression of Dehydroascorbate Reductase Confers Tolerance to Methyl Viologen and Salt Stresses in Tomato

As an important antioxidant for plants and humans, L-ascorbic acid (AsA, vitamin C) can scavenge reactive oxygen species (ROS) and can be regenerated from its oxidized form in a reaction catalyzed by dehydroascorbate reductase (DHAR). To analyse the effect of overexpressing DHAR on tomato (Solanum lycopersicum), an expression vector containing potato cytosolic DHAR (DHAR1) or chloroplastic DHAR (DHAR2) cDNA driven by a cauliflower mosaic virus 35S promoter was transferred into tomato plants. Compared with the wild type (WT), DHAR1 overexpression increased DHAR activity and AsA content in both leaves and fruits, while DHAR2 overexpression increased DHAR activity and AsA content mainly in leaves. DHAR1 and DHAR2 overexpression increased the chlorophyll content and photosynthetic rate of transgenic lines, but had no effect on plant height and stem diameter. Furthermore, the germination rate, plant fresh weight, seedling length and chlorophyll content of transgenic DHAR1 and DHAR2 plants under salt stress were higher than those of WT plants. In addition, the transgenic plants also exhibited considerable tolerance to oxidative damage induced by methyl viologen (MV). Taken together, these results indicated that overexpressing potato DHAR1 and DHAR2 enhanced the level of AsA in tomato and, consequently, increased the tolerance of tomato to salt and MV stress.