Effect Of Low Temprature Stress On Photosynthesis And Chlorophy Ⅱ Fluorescence And Physiological Characteristics On Cotton Seedlings

[Object] Six cotton cultivars (lines), Xinluzao 13,297-5,81-3,4723, Xinluzao 36,134-1 were selected as materials in this study to research the effect of low temperature on Photosynthesis and ChlorophyⅡFluorescence and Physiological Characteristics in cotton seedlings leaves. After measuring the above-mentioned indexes on low temperature stress,the results was expected to reveal the differences between different cotton cultivars (lines) and provide a theory for selecting cultivars (lines) of strong low-temperature tolerance.[Methods] Cotton seeds of six cultivars (lines) were selected and sowed in 36 plastic basins,which diameter is 26cm and height is 16cm in greenhouse. The ground substance is mixture of vermiculite and soil. Each basin has 10 strains and 3 basins was set up as a duplicate. Maintain the substance humid during the germination period. Changes of Photosynthesis and ChlorophyⅡFluorescence and Physiological Characteristics in cotton seedlings were tested under low temperature stress (25℃/CK,15℃,5℃; with a light intensity of 40001x) for 24h,48h,72h and 96h, the fourth or fifth leafs below the apical meristem was used.[Results] The main results in this study were as follows:(1) The results showed that the net photosynthetic rate of cotton seedlings (Pn), transpiration rate (Tr), stomatal conductance (Gs) were decreased while the intercellular CO2 concentration (Ci) increased under the low temperature stress and the changes of Pn, Tr, Gs and Ci raised as the temperature stress being severer and time prolonged. Besides, there were significant differences at the changes of 6 cotton cultivars(lines).(2) The chlorophyll fluorescence parameters of cotton seedling changed as follows:the maximal recorded fluorescence intensity(Fm), photochemical efficiency of PSⅡ(Fv/Fm), potential photochemical efficiency(Fv/Fo), the performance index PI, while the origion fluorescence (Fo) obviously increased. The changes of chlorophyll fluorescence parameters increased as the temperature stress being severer and time prolonged. Besides, there were significant differences among 6 cotton cultivars(lines).(3)In the cold stress of different temperature, the cotton seedling's soluble protein content decreased first and increased later, the activities of SOD and POD increased first and decreased later, the activities of CAT continued to decline under the low temperature stress.[Conclusion] In conclusion, low temperature would damage cotton seedlings. There were significant differences among six cotton cultivars(lines) under low temperature stress. The results also showed that there were significant differences of Gs, Fv/Fm and soluble protein content in six cotton varieties (lines). So the three indexes can be used as low-temperature tolerance indexes of cotton.