College of Horticulture，Nanjing Agricultural University，Key Laboratory of Southern Vegetable Crop Genetic Improvement，Ministry of Agriculture，Nanjing 210095，Jiangsu，China
Abstract：Taking nutrient solution as culture method，and salt sensitive cucumber（Cucumis sativus L.）cultivar‘Jinchun No.?2’as material，this experiment studies the effects of iso-osmotic Ca and NaCl stress on cucumber seedlings’chloroplast ultra-structure，chlorophyll content，photosynthetic characteristics and chlorophyll fluorescence parameters．The results indicated that the chlorophyll content was decreased by both salt stress，and the decreasing degree of NaCl stress was bigger than that of Ca stress．The ultra-structural analysis showed that under Ca stress，most of the chloroplasts were out of the cell wall and the numbers of grana thylakoid were decreased|whereas under NaCl stress the structure of chloroplast displayed deformation，and the grana lamellae became inflation，the hungry particles increased significantly．The net photosynthesis rate（Pn），stomatal conductance（Gs），PSⅡ photochemical quantum yield（Fv/Fm），PSⅡ actual photochemical efficiency（ΦPSⅡ）and photochemical quenching（qP）were all decreased by salt stress．However，the decreasing degree of Ca stress was less than that of NaCl stress．Intercellular CO2 concentration（Ci）was decreased by Ca stress，while was increased by NaCl stress．Thus，we concluded that the stomatal limitation was a dominate factor causing Pn decrease under Ca stress and non-stomatal factor was a dominate factor causing Pn reduction under NaCl stress．
