[Effects of cucumber leaf's PS II activity and electron transfer on its PS I activity in recovery process after...

Taking Cucumis sativus L. (Jinchun No. 4) as test material, through the determination of chlorophyll-a fluorescence transient and light absorbance at 820 nm, and in combining with chlorophyll quenching, this paper studied the recovery of cucumber leaf' s PS I and PS I activities and the interactions between PS I and PS II in the recovery process at room temperature (25 degrees C) and under different light intensities (0, 15, and 200 micromol x m(-2) x s(-1)) after six hours of low temperature (4 degrees C) and strong light (200 micromol x m(-2) x s(-1)) stress. Different extent of photoinhibition of the PS II and PS I occurred after the stress. During the recovery process at room temperature, the PS II activity recovered quickly and was insensitive to light intensity, while the PS I activity recovered quickly under weak light intensity (15 micromol x m(-2) x s(-1)) but slowly under strong light intensity (200 micromol x m(-2) x s(-1)), suggesting that after the chilling-induced photoinhibition, the reduced electron transfer from PS II to PS I protected the PS I from further inhibition, accelerating the recovery of PS I activity. In the breeding of chilling-resistant species of cucumber, it should not only pursue the higher chilling-resistance of PS II and faster recovery of PS II after chilling-induced photoinhibition, but also pay more attention to the coordinating of PS I and PS II during and after the chilling-induced photoinhibition. In the culture of cucumber, after chilling happened, a practical method to reduce light intensity would help the recovery of cucumber leaf PS I activity to protect the photosynthetic apparatus against photoinhibition.