选择苗期耐盐性较强的水稻(Oryza sativa)品种(株系)‘AB52’、‘02402’和‘02435’及敏感品种‘日本晴’,在网室周转箱内,设置5 000和8 000 mg·L^-1 NaCl两种盐处理,以清水为对照,研究盐胁迫下苗期水稻植株不同部位Na⁺和K⁺的吸收和分配与品种耐盐性的关系。结果表明,盐胁迫下,株高、绿叶干重和绿叶面积下降,绿叶中的水分含量降低,但茎鞘中的水分含量有所上升。5 000 mg·L^-1 NaCl胁迫处理10 d,耐盐品种所受的生长影响和叶片伤害程度低于敏感品种,但8 000 mg·L^-1 NaCl胁迫处理下品种间差异变小。盐胁迫下,水稻植株吸收Na⁺和置换出K⁺,但不同器官部位中Na⁺和K⁺的区域化分布特征明显,各部位的Na⁺含量由低到高依次为绿叶、根、茎鞘和枯叶。下部老叶能优先积累较多Na⁺而枯黄;绿叶吸收Na⁺相对较少,维持较低的Na⁺水平,同时保持较高且稳定的K⁺含量;植株茎鞘通过选择性吸收大量Na⁺和置换出一部分K⁺到叶片中,保持绿叶较稳定的K⁺含量和相对较低的Na⁺含量,维持较高的K⁺/Na⁺比,从而使植株少受盐害。敏感品种‘日本晴’在盐胁迫下绿叶中的Na⁺含量相对较高,且5 000 mg·L^-1 NaCl胁迫下绿叶Na⁺含量已接近高值,与在8 000 mg·L^-1 NaCl胁迫下差异不大,而耐盐品种绿叶吸收较少的Na⁺。另一方面,耐盐品种茎鞘的含K⁺相对较高,在盐胁迫下能吸收容纳较多的Na⁺,而绿叶中K⁺/Na⁺比较高。可以认为,绿叶的K⁺/Na⁺比可作为一个衡量耐盐性的相对指标。

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.