室外盆栽条件下盐胁迫对甜高粱光系统Ⅱ活性的影响

Effects of Salt Stress on Photosystem Ⅱ Activity in Sweet Sorghum Seedlings Grown in Pots Outdoors

室外盆栽条件下,设置2个NaCl浓度(100mmol L-1和200mmol L-1),调查盐胁迫对甜高粱光合特性和光系统II(PSII)活性的影响。结果表明,叶片Na+离子含量与Na+/K+比随盐浓度增加和处理时间延长而增加。净光合速率(Pn)、光系统II开放反应中心天线转化效率(Fv′/Fm′)、光化学猝灭系数(qP)和光系统II实际光化学效率(ΦPSII)随盐浓度的增加而降低,非光化学猝灭(NPQ)随盐浓度增加而增加;100mmol L-1处理组的Pn、Fv′/Fm′、qP和ΦPSII随处理时间延长有所恢复,但200mmol L-1处理组无此现象。光系统II(PSII)最大光化学效率(Fv/Fm)在100mmol L-1NaCl处理时变化较小,但在200mmol L-1NaCl处理时明显下降。短期盐胁迫未影响荧光诱导动力学曲线,而200mmol L-1NaCl处理5d后荧光诱导动力学曲线O-K和O-J相上升。进一步研究证明,PSII的失活速率在2个盐浓度下均无明显变化,而修复速率在200mmol L-1盐浓度处理5d后降低明显。因此,认为室外盆栽条件下盐胁迫造成甜高粱碳同化能力降低并改变PSII激发能分配;叶片Na+离子含量的大幅增加会导致PSII活性下降及光抑制,这与PSII失活速率无关,主要是失活PSII修复速率受抑制的结果。这对理解户外盐胁迫条件下C4作物的光抑制机制具有一定意义。

The effects of the different NaCl treatments （100 mmol L-1, 200 mmol L-1） on photosynthetic characteristics and the photosystem Ⅱ （PSⅡ） activity in sweet sorghum seedlings grown in pots outdoors were carefully investigated in this study. The Na＋ content and the ratio of Na＋/K＋ in leaves increased significantly with increases of NaCl concentration and treatment time. The net photosynthetic rate （Pn）, the efficiency of excitation energy captured by open PSII reaction centers （Fv /Fm ）, the photochemical quenching （qP） and the actual photosystem II efficiency （ΦPSII） all decreased while the non-photochemical quenching （NPQ） increased greatly with the increasing of NaCl concentration. In addition, Pn, Fv /Fm , qP, and ΦPSII had an ameliorative trend in the 100 mmol L-1 NaCl treatment, but this phenomenon did not appear in 200 mmol L-1 NaCl treatment. The maximum quantum yield of photosystem II photochemistry （Fv/Fm） was slightly affected in 100 mmol L-1 NaCl treatment, whereas distinct decreased in 200 mmol L-1 NaCl treatment. The chlorophyll fluorescence kinetic curves exhibited no changes at the beginning of NaCl treatment, while the rising speeds of O-K and O-J phases increased markedly in the 200 mmol L-1 NaCl treatment after five days. Furthermore, the photoinactivation rate of PSII did not change in both treatments while the repair rate was depressed significantly after five days treatment of 200 mmol L-1 NaCl. Therefore, we suggest that under salt stress the decrease of carbon assimilation in leaves of sweet sorghum seedlings grown in pots outdoors is mainly due to the accumulation of Na＋, and salt stress alters the excited energy distribution. During salt stress outdoors, the decline of PSII activity is majorly attributed to the depression of the repair rate of the photoinactivated PSII, rather than the photoinactivation rate under high light. It is helpful to understand the mechanisms of photoinhibition in C4 crop outdoors under salt stress to some extent.