| Tobacco(Nicotiana tobacum L.) is one of the important cash crops in China.Tobacco platation is very sensitive to the ecological environment because it origins from the tropic region with plentiful rainfall. Tobacco platation areas are throughout the country in China, and the yield and the quality of tobacco leaves in variuos growing areas are very different. Environmental conditions not only influences the morphology and the agronomic characters of tobacco leaves, but also directly affects the chemical composition and inner quality. Therefore, exploring the role of key material metabolism in the formation of tobacco leaf quality and finding effective measures to alleviate stressful environmental effects on tobacco production have very great realistic significance. This paper, taking tobacco plants and seeds as materials,carried out the following studies:(1) effects of different growth temperature on polyphenols metabolism in tobacco leaves at different growth stages;(2) differential responses and comparison of polyphenols metabolism under drought and low temperature stress in tobacco seedlings;(3) effects of seed priming with salicylic acid(SA), calcium chloride(CaCl2) and glycine betaine(GB) on improvement of stress resistance of tobacco seeds and seedlings. The results were presented as follows:1. Effects of different growth temperature on polyphenols metabolism in tobacco leaves at different growth stagesUsing tobacco plants(cv. Yunyan 87) as materials, the changes of polyphenols content and their metabolism related enzyme activities and gene expression were detected during the transplanting to resettling stage, resettling to squaring stage and mature stage of tobacco during different growth temperature simulated in artificial climate chambers similar to the temperatures in Jiangchuan of Yunnan, Zunyi of Guizhou, and Xiangxian of Henan province. The results indicated that during different growth stages of the tobacco plants, the changes of polyphenols content and their metabolism related enzyme activities and gene expression were different significantly under different growth temperatures. Before mature stage, total phenol and lignin content in tobacco leaves decreased obviously, and the total phenol content under the lower temperature(temperatures averaged 16 ℃) remained at a relatively higher level at the stage of transplanting to resettling, but the higher temperature(temperatures averaged 25 ℃) was more favorable to maintaining the total phenolcontent at higher level at the stage of resettling to squaring. After entering mature stage, total phenol content in tobacco leaves began to rise, and the accumulation of total phenol under the higher temperature(temperatures averaged25℃) raised to the highest level by the end of treatment. The activity changes of the key enzymes for polyphenol metabolism including PAL, C4 H, 4CL, CAD were consistent with the change of total phenol and lignin content, but the changes of gene expression of these key enzymes were different significantly and were not consistent with the change of the enzyme activity. In addition, The activities of PPO, POD both involved in lignin synthesis methods and participated in polyphenol oxidative decomposition showed the tendency of increasing at the different growth stages of tobacco, but the difference was significant among different temperature treatment. In general, the temperature conditions of Xiangxian of Henan province that showed slightly lower at earlier stage and higher at later stages is more suitable to the accumulation of polyphenols, and the temperature conditions of Jiangchuan of Yunnan province that exibited higher at earlier stage and lower at later stage is not conducive to the accumulation of polyphenols.2. Differential responses and comparison of polyphenols metabolism under drought and low temperature stress in tobacco seedlingsUsing tobacco plants(cv. Yunyan 203) as materials, tobacco seedlings were treated under drought and low temperature stresses, and the changes of polyphenols content and their metabolism related enzyme activities and gene expression were detected during the drought and chilling stresses. The results indicated that there were varietal differences between drought and low temperature stress on contents of total phenol and lignin, the key enzyme activities and gene expression. At the early stage of the drought stress, content of total phenol increased significantly, and up to a maximum level at 24 h, and then gradually decreased with the prolonged stress.Whereas, the total phenol content decreased consistently but lignin content increased under the low temperature stress. The activity changes of the key enzymes for polyphenol metabolism including C4 H, 4CL, CAD and their gene expression were consistent with the change of total phenol and lignin content under drought and low temperature stress, although PAL activity under drought stress was higher than that under low temperature stress, and PAL gene only expressed significantly under low temperature stress. In addition, activities of PPO and POD participated in polyphenol oxidative decomposition also increased significantly, especially under drought stress.3. Effects of seed priming with salicylic acid(SA), calcium chloride(CaCl2) and glycine betaine(GB) on improvement of stress resistance of tobacco seeds and seedlingsUsing the tobacco variety(cv. Yunyan 203) as materials, tobacco seeds were primed with different concentration of exogenous salicylic acid, calcium chloride and glycine betaine solution, and the priming effects of salicylic acid, calcium chloride and glycine betaine on seed germination and seedling growth of tobacco under the normal culture, drought, low temperature and drought and low temperature intercross stress. The results indicated that appropriate concentration of salicylic acid, calcium chloride and glycine betaine could improve significantly the germination potential,germination rate and germination index of tobacco seeds, shorten mean germination time, increase the root and shoot length, and fresh and dry weight of tobacco seedings under normal culture, drought, low temperature, drought and low temperature doubles stress conditions, especially which 0.5 mmol·L-1SA, 1 mmol·L CaCl2, and 15 mmol·L GB had better priming effects. Further studies showed that priming with 1 mmol·L CaCl2 and 15 mmol·L GB could significantly improve TTC reducing capacity and total chlorophyll content of tobacco seedlings under low temperature and drought and low temperature intercross stress, and decrease electrolyte leakage rate of tobacco seedlings under drought stress, thereby enhancing seedings’ resistance to drought and low temperature stress. |
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