The Effects of Exogenous Ascorbic Acid on the Mechanism of Physiological and Biochemical Responses to Nitrate Uptake in Two Rice Cultivars (Oryza sativa L.) Under Aluminum Stress

Abstract

As a major antioxidant in plants, ascorbic acid (AsA) plays a very important role in the response to aluminum (Al) stress. However, the effect of AsA on the mitigation of Al toxicity and the mechanism of nitrate nitrogen (NO3 −–N) uptake by plants under Al stress are unclear. In this study, a hydroponic experiment was conducted using peak 1 A rice (sterile line, Indica) with weaker resistance to Al and peak 1 superior 5 rice (F1 hybrid, Indica) with stronger resistance to Al to study the effects of exogenous AsA on the physiological and biochemical responses to NO3 −–N uptake by rice roots exposed to 50 μmol L−1 Al. Al stress induced increases in the concentrations of H2O2 and malondialdehyde (MDA) and in the activities of antioxidant enzymes [such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)]. Plasma membrane (PM) H+-ATPase and H+-pump activities, endogenous AsA content and NO3 −–N uptake in rice roots decreased under Al stress. After treatment with 2 mmol L−1 exogenous AsA combined with Al, concentrations of H2O2 and MDA in roots notably decreased, and endogenous AsA content and activities of SOD, POD, CAT, and APX in rice roots increased significantly; furthermore, the interaction of PM H+-ATPase and the 14-3-3 protein was also enhanced significantly compared with that in control plants without AsA treatment, which clearly increased NO3 −–N uptake. Based on all of these data, the application of AsA significantly reduced the accumulation of H2O2 and MDA and increased the activities of PM H+-ATPase and the H+-pump by increasing the endogenous AsA content, the antioxidant enzyme activities, and the interaction of PM H+-ATPase and the 14-3-3 protein in the roots of the two rice cultivars under Al stress, thereby improving the uptake of NO3 −–N in rice.