The Research On The Effect Of Low Temperature Stress On Physiological Responses And Regulations Of Cotton

【Objective】The ’Xinluzao 41st’ cotton was used to study the physiological response to cold stress of cotton seedlings, in terms of membrane systems, antioxidant enzyme systems, osmotic adjustment system, photosynthetic systems, and the function of exogenous physiological regulator such as Salicylic acid(SA), chitosan(CTS) calcium in the mechanism of induction of cotton seedling cold tolerance. And it provided a theoretical basis for regulating the growth of cotton seedlings under low temperature stress, and improved the cold resistance of cotton seedlings. 【Method】Utilized indoor pot experiment. In the experiment seedlings physiology response in different levels of low temperature stress in cotton, we set four temperature treatments:0℃, 5℃, 10℃, 15℃. In exogenous physiological regulation and its concentration screening tests, there were 7 kinds of exogenous physiological regulation, such as naphthalene acetic acid, humic acid, olefine thiazole. Filtrated salicylic acid, chitosan and calcium nitrate play key role in cold resistance in cotton. Then we set up six salicylic acid(SA) concentration gradient(0, 0.2, 0.4, 0.6, 0.8, 1.0 mmol?L-1), and five chitosan(CTS) concentration gradient(0, 0.3, 0.6, 0.9, 1.2 mmol?L-1), in order to screened of salicylic acid and chitosan concentration range. Finally we selected optimal concentration of exogenous modulator. Selected the eupuylla measured conductivity rate(REC), malondialdehyde(MDA), intercellular CO2 concentration(Ci), superoxide dismutase(SOD), transpiration rate(Tr) and other indicators. And we verified the effect of exogenous physiological regulator in the field. 【Results】1. The permeability of cell membrane increased under low temperature stress in cotton, and activity of protective enzymes and osmotic adjustment matter content increased at the beginning of low temperature stress, but with the continued low temperature stress, photosynthesis was significantly inhibited and amplitude decreased. We find 5 was the critical temperature of ℃cotton seedlings in low temperature stress. 2. In the experiment of screening better effect of exogenous physiological regulator regulate cotton cold resistance, the results showed that salicylic acid, chitosan, calcium chloride had better regulation of cotton to low temperature stress. 3. Salicylic acid could effectively improved the antioxidant enzyme activities and osmotic adjustment content of cotton leaves in low temperature stress, reduced the relative conductivity and MDA content, improved its low temperature tolerance, and 0.6-0.8mmol ? L-1 salicylic acid could effectively improved the cold resistance of cotton seedlings. 4. Chitosan could significantly reduce the relative conductivity and MDA content of cotton leaves. By increasing the SOD, POD, CAT activity and the content of soluble sugar, soluble protein, proline to accommodate low environment which 0.6mmol ? L-1 chitosan could effectively improve the cold resistance of cotton seedlings. 5. Cotton was treated with salicylic acid and chitosan complex processing cotton seedlings under low temperature stress would markedly enhance its capability of resistance to low temperature. The effect of the mixture of salicylic acid and chitosan treatment was better than the single application, at the same time the treatment of salicylic acid, chitosan and calcium nitrate ternary compound was superior to that of binary compound. 【Conclusion】The research showed that low temperature stress increased membrane permeability of cotton seedlings, photosynthetic rate declined, cotton itself could be adjusted protective activity and penetration to alleviate the low temperature damage, but this effect was limited. The exogenous regulators such as salicylic acid, chitosan and calcium nitrate could act the role of stress factors, therefore cotton could activate the corresponding defense mechanisms before chilling stress to alleviate the low temperature damage of cotton. And salicylic acid, chitosan and calcium nitrate had a synergistic effect in the induction of cotton seedlings cold tolerance.