Photosynthetic Characteristics and Ultrastructure of Chloroplast of Cucumber Under Low Light Density in Solar-Greenhouse

The photosynthetic characteristics and ultrastructure of chloroplast of cucumber in solar-greenhouse were studied. The result showed that the photosynthetic rate (Pn), photosyntheticability (A350), carboxylation efficiency, light saturation point and light compensation pointall declined remarkably under low light density, indicating that the photosynthetic characteristicsof cucumber were closely related to light environment. Under low light density, the minimalfluorescence (Fo), alterable fluorescence (Fv), photochemical efficiency of PSⅡ(Fv/Fm), steadyfluorescence in light (Fs), maximal fluorescence (Fm) and actual efficiency of PSⅡ(φPSⅡ)etcincreased, indicating that the photochemical activity and efficiency for solar energy transformationenhanced, thus the light proportion used to electron transport also increased. The chlorophylla, b, a/b and carotenoid of shading leaves decreased. However, the depressed extent of Chl a andChl a/b were obviously larger than that of Chl b. The number of chloroplast and starch grainin cucumber leaves descended, but that of grana and lamella increased as a shaded result. Thesize of chloroplast and starch grain of shading leaves minished.