Effects of salt and alkali stresses on growth and ion balance in rice (Oryza sativa L.)

Rice seedlings were stressed with salt stress or alkali stress. The growth, organic acids (OAs) and inorganic ions in stressed seedlings were measured to investigate the physiological adaptive mechanism by which rice tolerates alkali stress. The results showed that the injury effect of alkali stress on rice was stronger than salt stress. Under salt stress, inorganic anions were dominant in maintaining intracellular ionic equilibrium; however, under alkali stress, the contents of inorganic anions decreased, which caused a severe deficit of negative charge. The deficit of negative charge was remedied by greatly accumulated OAs, especially malate and citrate, and OAs were the dominant components and contributed to 61-81% of total negative charge, indicating that OA accumulation might be necessary for intracellular ion balance in rice. In addition, the OA metabolism adjustment of rice differed from that of other plant species, implying that rice may have a special alkali-tolerance mechanism.