Abstract:

Plant tolerance to salinity is genetically and physiologically complex. Many mechanisms, such as ion compartmentalization, osmotic regulation and scavenging of reactive oxygen species, have been demonstrated. Among them, anti-oxidative enzymes play an important role in salt tolerant characteristic in plants. In addition, the plasma membrane P-type H⁺-ATPase (EC 3.6.1.3) also involved in the plant response to salinity by regulating the ion homeostasis and so on. Although the relationship between salt stress and anti-oxidative enzymes or PM H⁺-ATPase has been studied widely, the results varied with the different experimental materials. An interesting shortcut is to comparatively study plants naturally adapted to salt versus their more salt-sensitive relatives. In this report, changes in the activities of antioxidative enzymes and plasma membrane H⁺-ATPase from root tips are compared between salt-sensitive and salt-tolerant rice cultivars under NaCl stress, in the presence or absence 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.

Key words: Oryza sativa, Salt stress, La3+, Antioxidative enzymes, Plasma membrane H+-ATPase