【作者】 魏学玲；

【导师】 杨颖丽；

【作者基本信息】 西北师范大学 ， 植物学， 2010， 硕士

【摘要】 重金属因制约植物生长发育和影响农产品安全问题而成为当今世界关注的焦点。铅是重金属污染中最严重和危害性较强的元素之一,具有移动性强、生物毒性大而且易被植物吸收的特点。植物在铅胁迫下生物大分子构象发生改变、引起电解质外渗、酶活性丧失及膜脂过氧化等,最终干扰植物的正常生理代谢和生长发育。此外,植物体内的铅可通过食物链进入人体内产生各种危害,包括造血功能、免疫功能及内分泌系统等多个系统的损伤。因此,植物在铅胁迫下的损伤与抗性机制的研究已成为研究热点。同时,如何缓解铅对植物的毒害作用,进而提高农作物的产量和品质也受到普遍关注。一氧化氮（Nitrogen oxide,NO）是一种广泛分布在生物体内的信号分子,参与植物体一系列生理过程的调控,如种子萌发、植物根和茎的生长发育、细胞凋亡以及植物防御病虫害、抵抗干旱、盐害、低温等一些生物与非生物胁迫的反应,因而其对植物种子萌发、生理生化特性影响的研究受到普遍关注,特别是关于NO缓解盐、干旱、高温等非生物胁迫对植物的影响。但有关NO对Pb²⁺胁迫下小麦种子萌发和幼苗生理特性影响的研究报道很少。本实验以两种小麦西旱2号和宁春4号为材料,研究了不同浓度的Pb²⁺、硝普钠（Sodium Nitroprusside,SNP）单独处理及SNP结合Pb²⁺处理下小麦种子萌发和幼苗生理生化特性的变化,试图为探明铅胁迫对小麦造成的毒害作用或为深入了解和认识小麦抗重金属污染的生理生化机制提供理论依据,进而通过调节NO水平来提高植物抗重金属胁迫的能力,为研究农作物铅毒害的缓解技术提供理论依据。主要研究结果及结论如下:1.两种小麦在低浓度铅处理下幼苗叶片叶绿素含量及超氧化物歧化酶（SOD）活性均无显著变化,而高浓度铅胁迫使其叶绿素a（Chla）、叶绿素b（Chlb）及叶绿素总量明显减少,但SOD活性显著升高,且相同浓度铅胁迫对小麦宁春4号幼苗叶片叶绿素的破坏作用明显强于对西旱2号的作用;不同浓度硝酸铅处理诱导两种小麦幼苗过氧化氢酶（CAT）、过氧化物酶（POD）和抗坏血酸过氧化物酶（APX）活性升高,但不影响丙二醛（MDA）含量;此外,Pb²⁺处理使小麦幼苗叶片脯氨酸含量升高,此效应具有浓度依赖性,但铅处理不影响可溶性糖相对含量。结果表明,铅胁迫对小麦西旱2号和宁春4号幼苗叶片叶绿素造成了破坏,却不同程度诱导抗氧化酶活性及脯氨酸含量升高,即表现出较强的抗氧化能力和渗透调节能力,增强了小麦对铅的耐受性,因而胁迫诱导两种小麦叶片MDA含量变化与对照比无显著性差异。2.低浓度的SNP处理对西旱2号小麦种子的发芽势、发芽率、茎长及根长无显著影响,却不同程度地诱导小麦幼苗叶片中CAT和POD活性升高,高浓度的SNP处理明显提高小麦种子的发芽势和发芽率,抑制幼苗根和茎的生长,降低幼苗叶片脯氨酸含量。此外,不同浓度的SNP处理均诱导幼苗叶片可溶性蛋白的含量增多,但对MDA和可溶性糖相对含量无显著影响。结果表明,高浓度外源NO供体SNP处理促进了小麦西旱2号种子的萌发,抑制其幼苗生长,低浓度SNP处理提高抗氧化酶活性和渗透性调节物的含量,因而SNP处理对细胞膜未造成明显的氧化损害。3.在Pb²⁺处理下,小麦种子发芽势、发芽率、幼苗根长和茎长均显著降低,25μmol/L SNP明显缓解Pb²⁺胁迫对种子萌发及幼苗生长的抑制作用。SNP处理提高了Pb²⁺胁迫下小麦幼苗叶绿素a、叶绿素b含量及叶绿素荧光参数F_v/F_m和F_v/F₀的比值,并诱导过氧化氢酶（CAT）活性升高,但100μmol/L SNP处理降低了过氧化物酶（POD）活性。此外,SNP诱导Pb²⁺胁迫下小麦幼苗叶片可溶性蛋白含量升高。结果说明,外源NO促进Pb²⁺胁迫下小麦种子萌发及幼苗生长,提高叶绿素和可溶性蛋白含量,诱导CAT活性升高,从而增强小麦对Pb²⁺胁迫的适应性。更多还原

【Abstract】 Heavy metal pollution was focused because of it’s inhibitory effect on plant growth and it’s safety problem on agriculture product. Lead is one of the most serious and stronger dangerous elements in heavy metal pollution, which shows strong mobility, high biology toxicity and easy absorbtion in plants. It has been indicated that lead stress leads to the biopolymer modification, electrolyte leakage, enzyme activity deficient and membrane lipid peroxidation, finally interfering with the growth and development of plant as well as normal physiological metabolism of plant. In addition, lead threatens human beings by entering food chain, leading to the injure of hematopoietic function, immune function and endocrine system. So the damage and resistance mechanism of plant in response to lead stress has become the hot spot issues. Meanwhile, it has been given attention at present that how do plant protect themselves against lead poisoning and then improve yield and quality of agriculture crops.Nitric oxide, which is commonly found as a signaling molecule, is involved in series of the regulation of plant processes, including seed germination, growth and development of roots and stems, cell apoptosis, plant defense and resistance responses to biotic and abiotic stresses, therefore the effects of this molecular on seed germination and plant physiochemical characteristics were focused, especially on alleviating abiotic stresses including salt, drought and higher temperature. However, there were few reports about exogenous NO on seed germination and physiological characteristics of wheat seedlings under Pb²⁺. In the present study, two wheat cultivars （Xihan 2 and Ningchun 4） were used to investigate the changes of seed germination and seedlings growth in response to Pb²⁺ or SNP treatment alone and Pb²⁺ + SNP treatment, which was to indicate the phyotoxicity of lead on wheat and to provide theoretical basis for knowing and understanding the mechanism of physiochemical responses of plant to heavy metal pollution, even to improve the tolerance of plant against heavy metals by regulating NO levels and provide the basis on alleviating Pb²⁺ toxicity in agricultural production. The main results and conlusions were as follows:1. There were no changes of chlorophyll content and superoxide dismutase （SOD） activity in two wheat seedlings exposed to lower Pb（NO₃）₂ concentration, while the amount of chlorophyll a, chlorophyll b and total chlorophyll was decreased and SOD activity was significant increased when wheat seedlings were subjected to higher Pb（NO₃）₂ concentration. The destroy to chlorophyll of Ning Chun was more serious than that of Xi Han in responses to the same Pb（NO₃）₂ stress. Different Pb（NO₃）₂ concentration induced enhanced activities of catalase, peroxidase and ascorbate peroxidase, but no significant changes in malondialdehyde （MDA） content. In addition, the amount of proline was increased by Pb（NO₃）₂ in two wheat seedlings in a concentration-dependent manner, but no change in soluble sugar content. The results suggested that chlorophyll content was destroyed and that the activities of antioxidases and the amount of proline were enhanced in wheat seedlings under the stress of Pb（NO₃）₂, thus the stronger effects of antioxidanted role and osmotic regulations were existed and enhanced wheat seedlings tolerance to Pb²⁺ stress. Therefore there was no significant difference in MDA content between the control and Pb（NO₃）₂-stressed wheat seedlings.2. Lower SNP treatment had no significant effects on germination rate, energy, root and shoot length, but induced enhanced the activities of CAT and POD. Higher SNP concentration significantly increased seed germination rate and energy, inhibited the growth of root and shoot length, as well as decreased the content of proline. In addition, different SNP concentrations induced synthesis of soluble protein, but no significant changes in the contents of malondialdehyde and souble sugar. These results suggested that higher SNP treatment promoted seed germination, and inhibited the seedling growth, while lower SNP treatment enhanced the activities of antioxidant enzymes and osmotic regulations so there was no oxidative damage on cell membrane.3. The results showed that Pb²⁺ treatment resulted in significant decreases in seed germination and seedling growth of wheat, 25μmol·L^-1 SNP could alleviate the inhibiton of Pb²⁺ on these indexes. Under Pb²⁺ stress, the levels of chlorophyll a, chlorophyll b and chlorophyll fluorescence decreased in wheat seedlings, whereas no significant changes in the activities of CAT and POD were observed in comparison with the control. The application of SNP abolished decreased rates of chlorophyll content and chlorophyll fluorescence, and induced increase of CAT activity. In addition, SNP led to increased soluble protein in wheat seedlings under Pb²⁺ treatment. Exogenous NO promoted wheat seed germination and seedling growth, improved the content of chlorophyll and soluble protein, increased the activities CAT so as to alleviate the poison of Pb²⁺ and enhance the adaptation of wheat seedlings to Pb²⁺ stress.更多还原