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

摘要

The photosynthetic characteristics and ultrastructure of chloroplast of cucumber in solar-greenhouse were studied. The result showed that the photosynthetic rate (Pn), photosynthetic ability (A_(350)) , carboxylation efficiency, light saturation point and light compensation point all declined remarkably under low light density, indicating that the photosynthetic characteristics of cucumber were closely related to light environment. Under low light density, the minimal fluorescence (Fo), alterable fluorescence (Fv), photochemical efficiency of PSⅡ(Fv/Fm), steady fluorescence in light (Fs), maximal fluorescence (Fm') and actual efficiency of PSⅡ (φ_(psⅡ))etc increased, indicating that the photochemical activity and efficiency for solar energy transformation enhanced, thus the light proportion used to electron transport also increased. The chlorophyll a, b, a/b and carotenoid of shading leaves decreased. However, the depressed extent of Chl a and Chl a/b were obviously larger than that of Chl b. The number of chloroplast and starch grain in cucumber leaves descended, but that of grana and lamella increased as a shaded result. The size of chloroplast and starch grain of shading leaves minished.