Photosynthetic-physiological and anatomical features of the silvered leaf of s ummer squash

The photosynthetic-physiological and anatomical features of silvered leaves of summer squash (Cucurbita pepo L.)were determinated. It was found that the net photosynthetic rates (Pn) of partially and entirely silvered leaves decreased 5.6%-30.2% and 21.7%-52.5%, respectively, compared to that of healthy leaves at most times within each day of trials. The highest Pn peak took place at different times in varied lea-(ves), at 10 a.m. for healthy, but at 8 a.m. for silvered leaves. The stomata limit value (Ls) of partially and entirely silvered leaves decreased 5.3%-23.5% and 22.0%-58.8%, respectively. The total chlorophyll and chlorophyll a, b contents also decreased in silvered leaves. However, the values of stomata conductance (Gs) and intercellular CO_(2 )concentration (Ci) were similar in healthy and silvered leaves. No regularity was observed between the variation trends of transpiration rate (Tr) of healthy and silvered leaves. Compared to that of healthy leaves, the fresh and dry weight of partially silvered leaves increased a little, whereas those of entirely silvered leaves decreased a little.For healthy leaves, it was also found that the space was enlarged slightly between the upper epidermis and the palisade cells in silvered leaves. The upper epidermal cells changed from flat, dense arrangement into glo-(bular), thin and scattered arrangement. The proportion of the upper epidermis thickness to the whole leaf thickness increased obviously in silvered leaves, but that of the palisade tissue thickness to the whole leaf thickness decreased at a small degree.