| Cucumber seeds and seedlings (Cucumis sativus L.) of two cultivars (Jinchun No.4,tolerant to high temperature; Zhongnong No.12,tolerant to high non-temperature) sensitive significantly to heat was selected as material in this study by mensutating seeds germination, chlorophyll fluorescence parameter, chlorophyll content, gas exchange parameter, changes of membrane permeability, changes of resistant-oxidation enzyme activities and modal index in cucumber seedlings to research the effects of high temperature stress on them and affecting mechanism.At the same time, comparing the difference of two cucumber cultivars.The results showed as follow :Germinating ability of cucumber seeds was inhibited under different high temperatures, and it was not obvious at 35℃ and very obvious at 40℃, 42℃ and 45℃. Germination rate, germination force, germination index, SVI and α-amylase activities decreased obviously. Lenth and fresh weight of root were reduced. And the extents of change was stronger with temperature rise, but they were inapparent between two cultivars.Some expansive growth phenomena occurred in two cucumber cultivars at 35℃/20 ℃(d/n) stress temperature, while the increases of stem diameter, fresh weight,dry weight of top and fresh weight, dry weight a of root are inhibited obviously. And all growth indexes were inhibited mightily at 40℃/25℃(d/n) and 42℃/27℃(d/n) stress temperature. There were some modal indexes differences between two cultivars. And the inhibiting degree to cultivar tolerant to high temperature (Jinchun No.4) was lower than that to Zhongnong No.12., but difference was not obvious.Net photosynthetic rate and stomatal conductance(Gs)decreased, however intercellular CO2 concentration increased, while transpiration rate was rising firstly and going down lastly. The cause of reduction of net photosynthetic rate in cucumber seedlings under high temperature stress might be mainly non-stomata limitation (The reason of Pn under one day 35℃/20℃(d/n) temperature stress was caused mainly by stoma). Chla content, Chlb content ,Chl(a+b) content and caro content all reduced after treatment for 5 days . Obvious changes happened to the ultrastructure of chloroplast in cucumber seedlings, and degrees of breakage relative to intention of treatments. Fv/Fm, φPS Ⅱ ,qP and Fv'/Fm' decreased with degree increasing and time prolonging of high temperature, while Fo increased. It was showed that the photosynthetic mechanism and activity of cucumber seedlings were not injured under 35℃/20℃(d/n) stress temperature, but they were injured under 40℃/25℃(d/n) and 42℃/27℃(d/n) stress temperature and... |
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