Abstract: By determining fluorescence parameters, composition of fatty acids, active oxygen species and activities of some antioxidant enzymes, the effects of chilling stress (4 oC) in the low light (100 μmol·m-2·s-1) on chilling-sensitive plants were studied. After 6 h of chilling stress (4 oC) in the low light (100 μmol·m-2·s-1), the maximal photochemical efficiency of PSII (Fv/Fm) of sweet pepper leaves decreased by 35.6%, and the oxidizable P700 decreased by 60%. However, chilling stress in the dark had no effect on both of them. Unsaturation of fatty acids in thylakoid membrane was accelerated, which might be helpful to stabilize photosynthetic apparatus. Distortion and swelling of grana caused by chilling in the dark probably decreased activities of antioxidant enzymes, which resulted in the accumulation of active oxygen species. On the contrary, photooxidation might be related to the disintegration and unstacking of grana. Chilling stress induced photoinhibition of PSII and PSI, and active oxygen species might be one of the factors causing the decrease of the oxidizable P700. PSI seemed to be more sensitive to chilling in the low light than PSII.

Key words: Sweet pepper (Capsicum annuum L.), Chilling temperature in the low light, Ultrastructure, Composition of fatty acids, Active oxygen species