【作者】 钟兰；

【导师】 王建波；

【作者基本信息】 武汉大学 ， 植物学， 2009， 博士

【摘要】 盐胁迫是影响农作物产量及质量的主要非生物因素之一。盐胁迫通过渗透胁迫和离子胁迫以及由此引起的营养不均衡影响植物的生长和发育,破坏植物的生理生化功能,最终导致植物细胞及植物体本身的死亡。因此,探究盐胁迫对农作物的影响以及盐害机理,提高农作物的耐盐性,从而提高盐渍土的农作物产量及质量,具有重要的理论和现实意义。小麦(Triticum aestivum L.)是目前我国主要栽培农作物之一。本研究通过对盐胁迫下耐盐品种德抗961与盐敏感品种鲁麦15号生理生化指标和DNA甲基化水平的分析,从生理生化角度和表观遗传水平上探讨植物的抗盐机制。盐胁迫使小麦的植株干重降低,鲁麦15号下降的幅度高于德抗961。随着盐浓度的增加小麦根丙二醛(MDA)含量增加,鲁麦15号增加的幅度高于德抗961。盐胁迫下小麦根K+／Na+比下降,鲁麦15号下降的幅度高于德抗961。小麦根超氧化物歧化酶(SOD),过氧化物酶(POD)和过氧化氢酶(CAT)的活性随着盐浓度的增加而增加,但德抗961增加的幅度高于鲁麦15号。由此可见,盐分对非盐生植物营养生长产生抑制作用,导致植物营养生长降低,抗盐品种具有较高的组成和诱导的抗氧化酶活性,膜脂过氧化程度较低,从而细胞膜受到的损伤程度较小,并维持较高的K+／Na+比,使植物受到较小的离子毒害。盐胁迫对植物的影响和植物的抗盐机理从生理学角度已开展了许多研究,但是有关盐胁迫和表观遗传的关系这方面的信息却很少。我们用高效液相色谱(HPLC)和甲基化敏感扩增多态性(MSAP)两种方法分别测定盐胁迫下德抗961和鲁麦15号根基因组DNA和CCGG序列甲基化的变化。HPLC分析显示两个品种的5-甲基胞嘧啶(5mC)含量都下降,MSAP分析显示两个品种的CCGG序列的甲基化发生明显变化,主要是发生了去甲基化,而且两个方法的结果都显示德抗961去甲基化的程度明显高于鲁麦15号。由此可知,盐胁迫引起的DNA甲基化变化在德抗961和鲁麦15号中是一致的,大部分的DNA甲基化变化是去甲基化,只是在前者去甲基化的程度较高,而且大部分发生在特定序列,而不是随机序列,表明盐胁迫引起DNA甲基化程度和类型的改变。5-氮杂胞苷是一种甲基化抑制剂。和单独NaCl处理相比,5-氮杂胞苷预处理过的小麦NaCl处理后植株干重显著增加,根MDA含量显著降低,K+／Na+比上升,SOD, POD和CAT的活性显著提高,5mC含量下降。所以,5-氮杂胞苷缓解了盐胁迫下小麦生长的抑制和离子毒害,小麦通过提高盐胁迫下小麦根SOD, POD和CAT的活性,降低了由于盐胁迫导致的膜脂过氧化,从而明显改善了植物的盐害,表明5-氮杂胞苷有利于提高小麦的抗盐性。更多还原

【Abstract】 Salinity is one of the major abiotic stresses affecting crop productivity and quality drastically. Salinity affects plant growth and development, destroys physio-biochemical function and results in death of plant cells and plant itself through osmotic stress, ionic stress and nutrition imbalance caused by excess of Na+ and Cl-. Thus it makes significant academic and practical sense to explore the effects of salinity on crop and the mechanism of salt stress, to improve the salt resistance and the output and quality of crop. Wheat(Triticum aestivum L.) is one of the major cultivated crops in our country now. In order to understand the mechanism of salt tolerance from the aspect of physio-biochemistry and epigenetics, the physio-biochemical traits and the change of DNA methylation of salt-tolerant wheat Dekang-961 and salt-sensitive wheat Lumai-15 under salt stress were examined.Dry weight declined in both cultivars under salt stress, with salinity stress being more prominent in sensitive Lumai-15. Upon exposure to salinity, an increase in lipid peroxidation level was found in the root of both Dekang-961 and Lumai-15, and it was higher in the latter. Salt stress induced the rate of K+/Na+ to decline in the root of the two cultivars, and the rate of decline was higher in Lumai-15. The activities of SOD, POD and CAT increased due to the increase in salt concentration in the root of Dekang-961 and Lumai-15, but the rate of increase was significantly higher in the former at both NaCl concentrations. So it can be seen that the growth of plants declined for salinity restrained the growth of glycophyte. The salt resistant cultivar showed higher level of constitutive and induced activities of antioxidant enzyme and lower lipid peroxidation, accordingly cell membrane injuring less; it kept the ratio of K+/Na+ higher, suffering lighter ionic toxicity.While plenty of physiological studies have described the negative effect of salt stress and the mechanism of salt tolerance, considerably less information exists on the epigenetic impacts of salt stress. Two complementary approaches were used to evaluate methylation changes in the root DNA of the two cultivars under salt stress: high pressure liquid chromatography (HPLC) and methylation-sensitive amplified polymorphism (MSAP). HPLC analysis showed global decrease of 5-methylcytosine (5mC) content in both cultivars, and MSAP analysis showed extensive methylation changes in CCGG sequences, with the net result being hypomethylation. However, the level of demethylation was higher in Dekang-961 than that in Lumai-15. Thereby, the present work suggested that most of the cytosine DNA methylation changes induced by salt stress could be related to hypomethylation events and most of them were directed to specific sequences, not random ones. Furthermore this response was the same in Dekang-961 and Lumai-15, and there was a larger demethylation in the former, suggesting salt stress induced changes of the degree and patterns of DNA methylation.5-azacytidine is a demethylating agent. Compared to only salt-treated treatment, plants treated with 5-azaC under salt stress had higher dry weight, lower MDA content, higher rate of K+/Na+, higher SOD, POD and CAT activities, lower DNA methylation in the root of the two cultivars. Consequerntly,5-azacytidine alleviated the restraint of growth and ionic toxicity of wheat under salt stress. With 5-azacytidine wheat obviously ameliorated the salt stress through increasing the activities of SOD, POD and CAT and reducing lipid peroxidation, suggesting 5-azaC was in favor of improving slat resistance of wheat.更多还原