RESUMEN
Dehydroascorbate reductase (DHAR) plays an important role in the recycling of ascorbic acid. In this work, we isolated the full length cDNA clones of two different DHAR genes (tentatively named as TaDHAR1 and TaDHAR2, respectively) from common wheat. Semi-quantitative PCR experiments showed that TaDHAR1 and TaDHAR2 were transcribed in many vegetative and reproductive organs examined in this work. Transient expression analysis using wheat protoplasts indicated that the protein products of TaDHAR1 and TaDHAR2 may be located in the cytoplasm. The cDNAs of TaDHAR1 and TaDHAR2 were expressed in the bacterial cells, and resultant histidine tagged recombinant proteins could be efficiently purified using nickel chelate affinity chromatography. In vitro enzyme activity assays revealed that the recombinant TaDHAR1 and TaDHAR2 proteins could all convert dehydroascorbate (DHA) to AsA. The two proteins exhibited higher activity levels at 37 degrees C than at 25 degrees C. Under the two temperature conditions, the optimal pH for TaDHAR1 and TaDHAR2 was both around 7.5. The major difference between TaDHAR1 and TaDHAR2 is the activity under pH 6.0 and 7.0 at 25 degrees C. The results and resources obtained in this study may be useful for further research into the physiological role of TaDHAR genes in AsA metabolism in crop plants under normal or stressed conditions.