[Objective] The purpose of this study is to explore the effect of different light intensities under chilling temperature on photosystem Ⅰ (PS Ⅰ ) and photosystem Ⅱ (PSⅡ) in cucumber leaves and the interaction between PS Ⅰand PS Ⅱ.[Method]By simultaneously analyzing chlorophyll a fluorescence transient and light absorbanee at 820 nm as well as analyzing chlorophyll quenching, the effects of chilling stress (4℃) combined with different light intensities (0, 100, 200, 400 μmol·m~(-2)·s~(-1)) on photoinhibition of PS Ⅰ and PS Ⅱin cucumber leaves were studied.[Result]The results showed that the maximal photochemical efficiency of PS Ⅱ (Fv/Fm) continually decreased with the increase of excess excitation energy ((1-qP)/NPQ).The maximum PS Ⅰ redox activity (△I/Io) also decreased significantly with the increase of excitation energy when excitation energy was relatively lower.However,when the excess excitation energy exceeded a certain level,the △Ⅰ/Ⅰo did not increase obviously with the increase of the excess excitation energy any more.[Conclusion ] Excess excitation energy under chilling temperature resulted in photoinhibition not only in PS Ⅰ but also in PS Ⅱ.However,too much excess excitation energy resulted in severely decrease in PS Ⅱactivity (Fv/Fm),which limited the transfer of photosynthetic electron from PSⅡ to the PSⅠprotecting the PSⅠ from further inhibition.%[目的]探讨低温胁迫下不同光强对黄瓜光系统Ⅰ(PS Ⅰ)和光系统Ⅱ(PS Ⅱ)的影响以及低温胁迫下两个光系统之间的相互作用机制.[方法]以冷敏感黄瓜品种津春4号为试材,通过同时测定黄瓜叶片叶绿素荧光快速诱导动力学曲线和对820 nm光的吸收曲线,结合叶绿素荧光淬灭分析,探讨了低温(4℃)与不同光强(0,100,200,400μmol·m~(-1)·s~(-1))结合处理对黄瓜PS Ⅰ和PS Ⅱ活性的影响.[结果]低温下,随过剩激发能((1-qP)/NPQ)的增加,PSⅡ最大光化学效率(Fv/Fm)持续下降;在过剩激发能较低时,PSⅠ活性(△Ⅰ/Ⅰ0)也随过剩激发能的增加而明显下降,但是当过剩激发能增加到一定程度时,PS Ⅰ活性不再随过剩激发能的增加而明显下降.[结论]在低温下,过剩激发能不但能够抑制黄瓜PS Ⅰ的活性也能抑制PSⅡ的活性,但是当过剩激发能增加到一定程度时,PSⅡ光化学活性的显著下降减少了光合电子向PS Ⅰ的供应,避免了PS Ⅰ光抑制的进一步加剧.
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