Abstract:

【Objective】 The purpose of this study is to explore the effect of different light intensities under chilling temperature on photosystemⅠ(PSⅠ) and photosystemⅡ(PSⅡ) in cucumber leaves and the interaction between PSⅠand PSⅡ. 【Method】 By simultaneously analyzing chlorophyll a fluorescence transient and light absorbance 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 PSⅠand PSⅡin cucumber leaves were studied. 【Result】 The results showed that the maximal photochemical efficiency of PSⅡ (Fv/Fm) continually decreased with the increase of excess excitation energy ((1－qP)/NPQ). The maximum PSⅠredox 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 PSⅠbut also in PSⅡ. However, too much excess excitation energy resulted in severely decrease in PSⅡactivity (Fv/Fm), which limited the transfer of photosynthetic electron from PSⅡ to the PSⅠprotecting the PSⅠfrom further inhibition.

Key words: cucumber, chilling temperature, PSⅠ, PSⅡ, photoinhibition, 820 nm transmission