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Lady godiva pumpkin seeds and seedlings (Cucurbita spp.) of three cultivars was selected as material in this study by mensutating seeds germination,chlorophyll content, gas exchange parameter,changes of membrane permeability,changes of resistant-oxidation enzyme activities and modal index in lady godiva pumpkin seedlings to research the effects of high temperature stress on them and affecting mechanism.At the same time,comparing the diffence of three lady godiva pumpkin cultivars.The main findings are as follows:1 Getrminating ability of lady godiva pumpkin seeds was inhibited under different high temperatures,and it was not obvious at 35℃and very obvious at 40℃.Germination rate,germination force and germination index decreased obviously.And the extents of changes was stronger with temperature rise.2 Some expansive growth phenomena occurred in three lady godiva pumpkin culticars at 35℃/25℃(d/n) stress temperature,while the increase of stem diameter,fresh weight,dry weight of top and fresh weight,dry weight of root are inhibited obviously.And all growth indexes are inhibited mightily at 40℃/30℃(d/n) stress temperature.3 Net photosynthetic rate and stomatal conductance 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 lady godiva pumpkin seedlings under high temperature stress might be mainly non-stomata limitation (The reason of Pn under two day 35℃/25℃(d/n) temperature srress was caused mainly by stoma).Chla content,Chlb content,Chl(a+b) content and caro content all reduced after treatment for 6 days.In all,the changes of the above paramerers were smaller under 35℃/25℃stress than 40℃/30℃.What’s more,the change degree of daliluoren pumpkin was lowest.4 Only as the increase of coercer intensity and time with the heat stress, POD activity improves in the seedling leaves of the hot pepper,but CAT activity declines,EL,MDA content and proline content increase;SOD activity is different because of dealing with differently. Resume stage in the normal atmospheric temperature, every index of the lady godiva pumpkin seedlings is recovery.The effect on plant of extreme high temperature is more prominent than 35℃/ 25℃to be; Every index of the daliluoren pumpkin and luoren№1 is superior to lvnong№1.5 Through the pilot found, in high-temperature stress pumpkin leaves electrolyte leakage rate and increase the content of MDA, SOD, POD, CAT, such as the protection of significant changes in the activity. These indicators of change and pumpkin varieties of heat resistance consistent performance, pumpkin varieties can be used as identification of the heat hardiness of indicators.
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