Dehydroascorbate reductase (DHAR, EC 1.8.5.1) helps to maintain redox pools of ascorbate (AsA) by recycling dehydroascorbate (DHA) to AsA. To investigate whether DHAR influences the acquired tolerance of rice plants to abiotic stresses, cDNA encoding DHAR (OsDHAR1) was isolated from rice and used to develop OsDHAR1-overexpressing transgenic rice plants regulated by a maize ubiquitin promoter. The incorporation and expression of the transgene was confirmed by polymerase chain reaction (PCR) and semi-quantitative reverse transcription PCR, real-time PCR, Western blot and enzyme activity. The overexpression of OsDHAR1 greatly increased the DHAR activity and the AsA/DHA ratio, following increase in AsA content and decrease in DHA content. In addition, the enzyme activity of monodehydroascorbate reductase, glutathione reductase and ascorbate peroxidase, which are related to the ascorbate-glutathione systems, was enhanced in the presence and the absence of salt stress in homozygous transgenic rice plants (OsDHAR1-OX1, -OX2) harbouring Ubi::OsDHAR1. In addition, OsDHAR1-expressing transgenic rice plants enhanced the redox state by reducing both hydroperoxide and malondialdehyde levels under salt and methyl viologen (MV) stress conditions, which led to better plant growth, ion leakage and quantum yield (Fv/Fm). Therefore, our results show that the overexpression of OsDHAR1 increases the adaptation of rice plants to salt stress, by maintaining the AsA pool, ion homoeostasis and redox homoeostasis. Finally, the findings of this study indicate that OsDHAR1 plays an important role in attenuating the deleterious effects of various abiotic stresses.

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SUMMARYThe Arabidopsis gene AVP1 encodes a vacuolar H+-translocating inorganic pyrophosphatase (enzyme classification (EC) 3.6.1.1) that functions as an electronic proton pump in the vacuolar membrane and affects growth development and the stress response in plants. The current study was conducted to evaluate the molecular properties of the Arabidopsis thaliana vacuolar H+-pyrophosphatase (AVP1) gene in rice (Oryza sativa L.). Incorporation and expression of the transgene was confirmed by semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR. Expression of the AVP1 gene in transgenic rice plants (TRP1 and TRP2) resulted in a significantly enhanced tolerance to 5·8 g/l NaCl under greenhouse conditions when compared with the control wild-type (WT) rice plants. Augmented AVP1 expression in the transgenic rice plants (TRP) also affected total biomass and improved ion homoeostasis through increased accumulation of Na+ ions in whole tissues when compared with control WT rice plants under high salinity conditions. The photochemical yield (Fv/Fm) values of TRP were higher than those of the WT rice plants, even though the values decreased over time in both the WT and transgenic (TRP1 to TRP8) rice plants. Furthermore, rice grain yield and biomass of the TRP were at least 15% higher based on culm and root weights, and panicle and spikelet numbers when compared with those of the WT rice plants during the 2010 and 2010 growing seasons in South Korea. Thus, these results suggest that ectopic AVP1 expression conferred tolerance and stress resistance to genetically modified transgenic crop plants by improving cellular ion homoeostasis in response to saline conditions, which enhanced rice yield and biomass under natural conditions in paddy fields.

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