| A sweet pepper (Capsicum annuum L.) line, 156, and a cultivar of cucumber (Cucumis sativus L.), Jinchun No.14, were used as materials to investigate the effects of chilling temperature (4 ℃) in the low light (100 μmol m-2s-1) on photoinhibition of PSI and PSII and their relationship in chilling-sensitive plants. Tobacco (wild type and the mutant, ΔndhB) was also used to study the possible function of cyclic electron flow around PSI upon exposure to chilling stress in the low light. The main results as follow: 1. Effects of chilling stress in the low light on photosynthesis of sweet pepper and the limiting factors during subsequent recoveryAfter chilling stress in the low light for different time, photosynthetic parameters determined under optimum conditions were analyzed. Decreases in Pn and Gs were accompanied by the increase of Ci after chilling stress in the low light. However, the decreases in Pn and Gs were accompanied by the decrease of Ci after chilling stress in the dark. It suggested that chilling in the light and chilling in the dark had different effects on photosynthesis, and non-stomatal limitation was the main limiting factor of photosynthesis. Water potential (Ψw) of sweet pepper leaves decreased markedly during chilling stress in the low light, but Ψw did not change in the dark. These results showed that stomata kept open under chilling stress in the low light, and stomata closed in the dark.The recovery of Pn needed about 8 h after 6 h chilling stress in the dark, but it took about 50 h to recover after chilling stress in the low light. These showed that chilling stress in the dark caused the decrease in activity of some enzymes involved in Calvin cycle, and chilling stress in the light might affect PSI besides enzyme activities.Effects of chilling stress on Mehler reaction and photorespiration were investigated in sweet pepper leaves. Chilling stress in the dark and the recovery process had little effect on k(PSII/(CO2 and Δk. However, chilling stress in the low light induced the marked increase of k (PSII/(CO2 at the end of stress, but did not affect Δk, which increased markedly during recovery process. The results indicated that Mehler reaction had an important role during the stress and photorespiration functioned during recovery process.2. Photoinhibition of chilling-sensitive plants under chilling stress in the low light and related physiological mechanismsFv/Fm in sweet pepper leaves decreased upon exposure to chilling in the low light and it could recover within 4 h. The oxidizable P700 also decreased markedly after 6 h chilling stress in the low light, and its recovery was consistent with that of Pn, both of which would take about 50 h to recover. It implied that PSI photoinhibition was the main factor limiting recovery of photosynthesis. Fv/Fm and the oxidizable P700 changed little in sweet pepper leaves upon exposure to chilling stress in the dark.During chilling stress in the light the decrease of Fv/Fm was accompanied by the decrease of Fo in sweet pepper leaves, which showed that chilling stress in the low light did not bring damage to PSII reaction centers but induced slightly PSII photoinhibition.At the end of chilling stress in the low light, Fv/Fm in sweet pepper leaves was lower than that in cucumber, and the oxidizable P700 was higher in sweet pepper leaves. During the stress, NPQ and the xanthophyll cycle conversion state (A+Z)/(V+A+Z) in cucumber were lower than that in sweet pepper. However, the accumulation of active oxygen species and the imbalance term, β/α-1, were higher in cucumber. All of the above might be main factors causing more sensitivity of PSI to chilling in the low light in cucumber leaves. During chilling stress in the low light, Fv/Fm and ETR in MV-fed sweet pepper leaves were higher than that of control, and the oxidizable P700 was not affected. These showed that chilling temperature induced photoinhibition of two photosystems by inhibiting electron transport to acceptors. In DTT-fed sweet pepper leaves, both Fv/...
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