NaCl胁迫抑制玉米幼苗光合作用的可能机理

用NaCl 100mmol/L处理玉米幼苗,216 h内不同时间分别测叶片光合速率及其它生理指标,结果表明随处理时间的延长,光合速率下降,气孔导度减小,细胞间隙CO2浓度先降低后升高(图1);叶片MDA(图5a)、Cl-、Pi(图4)及可溶性糖(图2b)含量增加;质膜透性增大(图2a);Chla/Chl b(图3b)及Fv/Fm(图5b)减小;MDH、PEPC酶活性降低(图6).细胞间隙CO2浓度的变化,说明光合速率下降的原因短时间内以渗透胁迫产生的气孔限制因素为主,长时间时以非气孔因素为主.Cl-多对细胞产生离子毒害,Pi的增多可竞争性地抑制RuBP羧化酶的活性.MDA的增加表明活性氧增多,活性氧通过使酶失活和膜伤害抑制细胞生长,使细胞内糖利用减少,可溶性糖含量增加,进而反馈性地抑制光合作用.活性氧还可以漂白叶绿素、增强光抑制及使与光合作用有关的酶失活,而抑制光合作用.因此,NaCl胁迫下光合作用降低的原因是多因素共同作用的结果,短时间内以气孔限制因素为主,长时间时以非气孔因素为主,在非气孔因素中活性氧的增加是主导因素.

The Possible Mechanisms of NaCl Inhibit Photosythesis of Maize Seedlings

Maize seedlings were treated with 100 NaCl mmol/L, Photosynthetic rate and other parameters were measured at different time in 216 h after NaCl stress. The results show that the photosynthetic rate decreased with time, while stomatal conductance decreased, substomatal CO 2 concentration decreased at first then increased gradually (Fig.1). MDA(Fig.5a), Cl -,Pi(Fig.4) and soluble carbohydrate (Fig.2b) contents increased, while Chl a/Chal b(Fig.3a) and Fv/Fm(Fig.5b) decreased, and the activity of MDH and PEPC decreased(Fig.6). The changes of substomatal CO 2 concentration indicate that the stomatal limitation caused by osmotic stress is dominating factor of the photosynthesis' decrease when the stress period is short, with the prolonging of stress period non stomatal inhibiting factor become the dominating ones gradually. The increase of Cl - content induce ionic damage to mesophyll cell, Pi can inhibit the activity of RuBPcase. The increase of MDA drop a hint the increase of active oxygen. Enzyme's inactive and membrane damage caused by active oxygen inhibit cell growth, as a result soluble carbohydrate's consumption decreased and its content increased, the soluble carbohydrate inhibit the photosynthesis through feedback inhibition. Active oxygen bleaches chorophyll and causes photoinhibition, and stimulates the degradation of enzymes which related with photosynthesis. In sum the reasons for inhibition of photosynthesis by NaCl stress are the results of interactions of many factors. The stomatal limitation is dominating in short period, non stomatal inhibiting factor become the dominating ones in longer period gradually. The increase in active oxygen is the basic non stomatal inhibiting factor.