Abstract: he effects of low light on photosynthetic and fluorescent characteristics of seedlings in cucumis sativus (shade susceptible 'Jinyan 2' and shade tolerant 'Deltastar') were investigated in the growth chamber. After treated 20 days under the low light Intensity (75-85 μmol·m^-2·s^-1), the photosynthesis pigment contents and the ratios of chlorophylls/carotenoids [Chl.(a+b)/Car.) in leaves of the two cultivars increased, and the values were higher in 'Deltastar' than in 'Jinyan 2'. While, the ratios of Chl.a/b decreased, especially in 'Deltastar'. The net photosynthesis rate (Pn) and water use efficiency (WUE) in the two cultivars decreased but the smaller reduction extents and higher values were observed in 'Deltastar'. There were some differences in effects of low light on the maximal photochemical efficiency of PSⅡ in the dark (Fv/Fm), the actual photochemical efficiency of PSⅡ in the light (ΦPSⅡ), the photochemical reaction rate (Prate), the linear whole-chain electron transport rate (J) and the partitioning proportion for photochemical reaction of light energy absorbed by PSⅡ (P) between two cultivars, which the that in 'Deltastar' increased markedly, nevertheless the ruleless changes of the that in 'Jinyan 2'. It indicated that light energy use capability in 'Deltastar' was stronger than that in 'Jinyan 2' under low light.

Key words: Cucumis sativus, seedling, low light, gas exchange, chlorophyll a fluorescence