等渗盐胁迫下Na^＋和Cl^-对大豆幼苗光合作用的离子效应

研究和比较了等渗(-0.53MPa)的PEG-6000、NaCl、钠盐(无Cl-)和氯化物(无Na )溶液处理6d对栽培大豆品种‘Lee68’(耐盐性较强)和‘N23674’(耐盐性较弱)幼苗光合作用的离子效应。结果表明:PEG-6000处理使两品种叶片叶绿素含量和Rubisco活性较对照低,但降幅不如同样渗透压的NaCl、钠盐(无Cl-)和氯化物(无Na )溶液明显。PSII最大光化学效率(Fv/Fm)、电子传递速率(ETR)和PSII光化学的有效量子产额(Fv'/Fm')在PEG-6000处理2d和6d时显著下降,但在3种等渗盐处理下,多显著下降。两品种叶片气孔导度(Gs)和净光合速率(Pn)在4种胁迫处理下均显著下降,其中在3种盐处理下更明显,但胞间CO2浓度(Ci)仅在PEG-6000处理时下降,在盐处理下反而升高。两品种叶片叶绿素含量、Rubisco活性、Fv/Fm、ETR、Fv'/Fm'、Pn、Gs等在氯化物(无Na )溶液处理的下降幅度和叶绿体中Cl-含量及其与Na 总量的增加幅度均大于钠盐(无Cl-)处理的,在耐盐性弱的‘N23674’品种中更明显。可见,在NaCl胁迫对栽培大豆幼苗光合作用的毒害效应中,渗透胁迫较轻,离子毒害较重,其中Cl-的毒害大于Na 的。

Ionic effects of Na+ and Cl- on photosynthesis in Glycine max seedlings under isoosmotic salt stress.

Ion-specific stress effects of Na(+) and Cl(-) on photosynthesis of seedlings of two soybean (Glycine max) cultivars (the salt-tolerant 'Lee68' and the salt-sensitive 'N23674') were studied and compared under isoosmotic (-0.53 MPa) solutions [PEG-6000, NaCl, Na(+) (without Cl(-)) and Cl(-) (without Na(+))] for 6 d. The results showed that the chlorophyll contents and the ribulose bisphosphate carboxylase/oxygenase (Rubisco) activities of seedlings of both cultivars were inhibited to a less degree by PEG-6000 than by NaCl, Na(+) (without Cl(-)) or Cl(-) (without Na(+)) solutions. The maximum photochemical efficiency of photosystem II (PSII) (F(v)/F(m)), electron transfer rate (ETR) and effective quantum yield of PSII photochemistry (F(v)'/F(m)') were lowered significantly by PEG-6000 treatment for 2 d and 6 d. But when treated with the three isoosmotic salt stresses, most of the above three indexes significantly declined. Leaf stomatal conductance (G(s)) and net photosynthetic rate (P(n)) in both cultivars were significantly decreased under the four isoosmotic treatments, and much more drops were observed in the three salt stresses, but the intercellular CO(2) concentration (C(i)) decreased by PEG-6000 treatment and increased by the three salt stresses. Higher decreases including chlorophyll content, Rubisco activity, F(v)/F(m), ETR, F(v)'/F(m)', P(n) and G(s), and higher contents of Cl(-) as well as the content of Cl(-) plus Na(+) in chloroplasts were all observed under Cl(-) (without Na(+)) treatment than those under Na(+) (without Cl(-)) treatment, especially for the salt-sensitive cultivar 'N23674'. The results indicate that, among the adverse effects of NaCl stress on photosynthesis of G. max seedlings, the ionic toxicity was stronger than osmotic stress, and the toxicity of Cl(-) was more severe than that of Na(+).