Effects Of Salt Stress And La～(3+) On Antioxidative Enzymes And Plasma Membrane H～+-ATPase In Roots Of Two Rice Cultivars With Different Salt Tolerance

Two rice (Oryza sativa L.) cultivars, i.e. Wuyunjing 8 (salt-sensitive) and Jiucaiqing (salt-tolerant), were used to investigate the changes in the activities of antioxidative enzymes and plasma membrane H⁺-ATPase from root tips under NaCl stress, in the presence or absence of La³⁺. The main results were presented as follows:The length of roots were suppressed in two rice cultivars with the prolongation of salt stress. Index of salt tolerance were higher in salt-tolerant cultivar than in salt-sensitive one. The result indicated that under NaCl stress root growth were slighter suppressed in Jiucaiqing than that of Wuyunjing 8.The concentration of MDA was enhanced in two rice cultivars under salt stress. The degree of increment was higher in salt-sensitive rice than in salt-tolerance one. However, the parameters were decreased by the inclusion of La³⁺.The results indicated that CAT and POD activities, but not SOD and APX activities, were higher in salt-tolerant cultivar than in salt-sensitive one. Under NaCl stress, especially in the range of 200-300 mmol L^-1 NaCl, external La³⁺ increased the activities of CAT, SOD, APX, and POD in salt-tolerant rice, but not in salt-sensitive cultivar, which suggests that external La³⁺ can lighten the oxidative damage of rice seedling roots, mainly at high salt concentration range.Plasma membrane H⁺-ATPase activities were suppressed by 30% under NaCl stress in salt-sensitive cultivar, and La³⁺ effectively alleviated such suppression. On the contrary, in salt tolerant cultivar, H⁺-ATPase activity increased by 32% under NaCl treatment, and La³⁺ had little effect on the activities. Semi-quantitative RT-PCR analysis demonstrated that the changes in PM H⁺-ATPase activities and La³⁺ effect under salt stress might occur at transcriptional level. Taken together, the data suggested that in salt-sensitive rice Wuyunjing 8, the root Cytosolic Na⁺ concentration seems to be more dependent on the Na⁺ intracellular compartmentation capacity, while in salt-tolerant rice Jiucaiqing, NaCl induces plasma membrane H⁺-ATPase gene expression, indicating that the roots require increased H⁺-electrochemical potential gradient for the maintenance of ion homeostasis for osmotic regulation. In addition, the different effects of La³⁺ on the activities of anti-oxidative enzymes and plasma membrane H⁺-ATPase indicate that there might be completely different salt stress responding mechanisms between salt-sensitive and salt-tolerant rice cultivars.