关键词: 水稻, 盐胁迫, 耐盐性, Na⁺, K⁺, 吸收分配规律

Abstract:

Aims Salinity is a serious abiotic stress that adversely affects rice productivity and quality. Proper regulation of ion flux is necessary for cells to keep concentrations of toxic ions low and to accumulate essential ions. The purpose of our experiment is to detect differences in the physiological response and absorption and distribution of Na⁺ and K⁺ among rice seedlings tolerant or sensitive to salt stress.

Methods Seedlings of three salt-tolerant varieties (‘AB52’, ‘02402’ and ‘02435’) and a sensitive variety (‘Nipponbare’) were grown under different salt stresses (fresh water, 5 000 and 8 000 mg·L^-1 NaCl). We recorded agricultural traits and measured Na⁺ and K⁺ contents with ICP.

Important findings Seedling length, green leaf area, dry weight and moisture content of green leaves declined under salt stress, while moisture content of stems and sheaths increased. Plant growth and leaf damage of salt-tolerant varieties were less than that of the salt-sensitive variety when they were grown under 5 000 mg·L^-1 NaCl for 10 d. However, differences among varieties grown under 8 000 mg·L^-1 NaCl were small. Under salt stress, rice seedling absorbed Na⁺ from roots and discharged K⁺. There was a regular range of Na⁺ and K⁺ in seedlings. The Na⁺ concentration in different organs ranged from low to high. Generally, younger green leaves contained less Na⁺ than dried leaves under normal condition, and still had low Na⁺ and high K⁺ concentrations under salt stress. The Na⁺ concentration in green leaves of the salt-sensitive variety was the highest under 5 000 mg·L^-1 NaCl; however, the salt-tolerant varieties reached the highest Na⁺ level under 8 000 mg·L^-1 NaCl. It seems a major character of salt tolerance mechanism in rice seedling that the confine distribution area of Na⁺ in shoots maintaining green leaves a homeostasis of Na⁺, K⁺ with higher K⁺/Na⁺ ratio by selective transportation K⁺ from stems and sheathes to green leaves and roots, and interception Na⁺ in stems and sheathes. The result that K⁺ concentration in stems and sheathes of the salt-tolerant varieties were higher than that of the sensitive variety suggests that it could cause less Na⁺ concentration and maintain higher K⁺/Na⁺ ratio in green leaves. Therefore, K⁺/Na⁺ ratio in green leaves could be an index for evaluating salt tolerance.

Key words: rice, salt stress, salt tolerance, Na⁺, K⁺