Effects of Low Light on Photosynthetic and Fluorescent Characteristics of Seedlings of Cucumis sativus

The effects of low light on photosynthetic and fluorescent characteristics of seedlings of Cucu- mis sativus (shade susceptible‘Jinyan 2’and shade tolerant‘Dehastar’) were investigated in the growth chamber.After 20 days of treatment under low light intensity(75-85mol·m~(-2)·s~(-1)),the photosynthesis pigment contents and the ratios of chlorophylls/carotenoids[Chl.(a+b)/Car.] in leaves of the two culti- vars 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 in the two eultivars 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 PSⅡin the dark (Fv/ Fm),the actual photochemical efficiency of PSⅡin the light(ΦPSⅡ),the photochemical reaction rate (Prate),the linear whole-chain electron transport rate and the partitioning proportion for photochemical reac- tion of light energy absorbed by PSⅡbetween the two cuhivars,which increased markedly in‘Dehastar’, while less changes were obsearved in‘Jinyan 2’.It indicated that light energy use capability in‘Deltastar’was stronger than that in‘Jinyan 2’under low light.