【作者】 黑淑梅；

【导师】 佘小平；

【作者基本信息】 陕西师范大学 ， 植物学， 2005， 硕士

【摘要】 铬作为工业“五毒”之一,是环境中一种具有潜在危害性的污染物,其中的六价铬(Cr⁶⁺)因其氧化性和对皮肤的高渗透性,是一种毒性很强的人和动物致畸、致癌剂。目前关于Cr⁶⁺对植物生长发育方面影响的研究工作主要集中在植物体对Cr⁶⁺的吸收、积累,Cr⁶⁺胁迫下植物的外在表型、内部结构、酶活性变化、过氧化胁迫及光合系统等方面。已有研究表明,许多重金属污染（如Ni、Cd、Hg、Cr等）会对人和动物细胞的DNA造成损伤,表现为:（1）导致期外DNA合成速率的大幅度提高;（2）造成DNA的断裂;（3）引起DNA和蛋白质以及DNA链间交联,进而干扰基因组的正常表达,导致癌症和其它疾病的发生。但关于重金属污染对植物细胞DNA的损伤效应仅见于少数报道,Cr⁶⁺对植物DNA的损伤效应更未见研究。 本文研究了不同浓度Cr⁶⁺处理72h对不同苗龄小麦植株的生长、DNA代谢以及根尖细胞PCD的影响,试图了解Cr⁶⁺影响主要农作物小麦生长发育和产量的机制,探索重金属对植物的伤害机理和重金属胁迫下细胞程序性死亡发生的规律,并为植物防御重金属伤害和耐重金属胁迫机制研究奠定理论基础。本文的主要内容如下: 一.Cr⁶⁺对小麦幼苗生长的影响。研究发现,Cr⁶⁺明显影响3d和10d龄小麦幼苗的生长。具体表现为除5-20mg·L^-1和5-100mg·L^-1Cr⁶⁺分别促进3d和10d龄小麦幼苗根数增加外,所试浓度Cr⁶⁺均表现出降低两苗龄幼苗根长、苗高、地上部分和根系鲜重、干重的效应。所试浓度Cr⁶⁺对根系生长的抑制效应大于地上部分,3d龄幼苗比10d龄幼苗对Cr⁶⁺胁迫更敏感。 二.Cr⁶⁺对小麦幼苗DNA的损伤效应。 1.Cr⁶⁺对小麦幼苗DNA含量的影响。实验结果表明,Cr⁶⁺导致小麦幼苗叶片和根系DNA含量显著降低,其中根系DNA含量下降的幅度大于叶片;3d龄幼苗叶片和根系DNA含量下降的幅度大于10d龄幼苗。 2.Cr⁶⁺对小麦幼苗DNA断裂及DNA链间交联的影响。实验结果表明,（1）60-100mg·L^-1Cr⁶⁺处理的3d龄幼苗根系的DNA增色效应值低于对照值,因此60-100mg·L^-1Cr⁶⁺有促进3d龄幼苗根系DNA链间交联的效应,可见DNA链间交联为Cr⁶⁺胁迫下3d龄小麦幼苗根系DNA损伤效应之一,一定浓度Cr⁶⁺有可能通过诱发DNA链间交联进而抑制3d龄小麦幼苗根系的生长。（2）5-100mg·L^-1Cr⁶⁺更多还原

【Abstract】 Abstract As one of five poisons in industry, chromium is a latent and jeopardized environmental pollutant. Due to its powerful oxidizing capabilities and ability to cross biological membranes, Cr⁶⁺ is considered as the most hazardous carcinogens and mutagens to animals and human. At present, the studies on the effects of Cr on plants were mainly focused on uptake and accumulation of Cr, hindrance on plant growth, damages to internal structures, and variety in activities of enzymes, oxidative stress and lesions of photosynthetic system and so on. Some studies indicate that heavy metals （e.g. Ni、Cd、Hg and Cr） are potent inducers of tumors in experimental animals and human cell, and caused a variety of DNA damages such as increasing of the rate of unscheduled DNA synthesis, DNA strand breaks, DNA-protein crosslinks, DNA interstrand crosslinks, as well as expression of genome. But there are a few reports on the DNA damages of plants caused by heavy metals, say nothing of Cr⁶⁺.Therefore, in this study, the investigations were carried out on wheat （Triticum aestivum cv. Xiaoyan No.22） seedlings with different concentrations of Cr⁶⁺ in hydroponics culture. Effects of Cr⁶⁺ on the growth of wheat seedlings, DNA metabolism and PCD in root tip cells were conducted in different stages of wheat seedlings （3-day-old seedlings and 10-day-old seedlings） after 72h of Cr⁶⁺treatment, in order to discuss the mechanisms that Cr⁶⁺ affects the growth and yields of wheat seedlings, that heavy metal causes damage to plants, and that rule of PCD happens under heavy metal stress, so that to establish the theoretic ground for mechanism of recovery and endurance to heavy metal stress in plants. The results were as follows:Effect of Cr⁶⁺ on the growth of wheat seedlings.Studies found that Cr⁶⁺ could clearly affect the growth of 3-day-old seedlings and 10-day-old seedlings. Root length, shoot height, fresh weight and dry weight of roots and shoots of seedlings were all decreased by Cr⁶⁺ tested concentrations, except that root number was increased with 5-20mg·L^-1 Cr⁶⁺ in 3-day-old seedlings and with 5-100mg·L^-1Cr⁶⁺ in 10-day-old seedlings.The growth of roots was reduced by Cr⁶⁺ treatment more than the growth ofshoots. And the growth of 3-day-old seedlings was more sensitive to Cr⁶⁺ stress than that of 10-day-old seedlings."1. Effect of Cr⁶⁺ on DNA damages in wheat seedlings.1. Effect of Cr⁶⁺on DNA content in wheat seedlings. The trial results indicated that DNA contents in roots and shoots of seedlings were all markedly reduced by Cr⁶⁺ tested concentrations. Moreover, the declining extent of DNA content in roots of seedlings was bigger than that in shoots of seedlings, and the declining extent of DNA content in shoots and roots of 3-day-old seedlings was still bigger than that of 10-day-old seedlings.2. Effect of Cr⁶⁺ on DNA fragmentation and DNA interstrand crosslinks in wheat seedlings. The results showed that: （1） The hyperchromicity of DNA in roots of 3-day-old seedlings was bigger than that of control seedlings in the range 5-40mg·L^-1 Cr⁶⁺, also the hyperchromicity of DNA in shoots of 3-day-old seedlings and 10-day-old seedlings and roots of 10-day-old seedlings was bigger than that of control seedlings in the range 5-100mg·L^-1Cr⁶⁺. These indicated that DNA fragmentation happened, and that DNA fragmentation was one of DNA damages effects. （2） The hyperchromicity of DNA in roots of 3-day-old seedlings was smaller than that of control seedlings in the range of 60-100mg·L^-1Cr⁶⁺, which means DNA interstrand crosslinks. And DNA interstrand crosslinks was another of DNA damages effects. So, DNA fragmentation and DNA interstrand crosslinks are possible the mechanisms of inhibition of growth in wheat seedlings.三. Effect of Cr⁶⁺ on DNA methylation in wheat seedlings. The results indicated that: （1） The 5-MeC content in the shoots DNA of 3-day-old seedlings and 10-day-old seedlings with 5-100mg·L^-1Cr⁶⁺ treatment were all higher than that of control seedlings. （2） The 5-MeC content in the roots DNA of 3-day-old seedlings with 5-100mg·L^-1Cr⁶⁺ treatment were all higher than that of control seedlings. But in the roots DNA of 3-day-old seedlings, exception that the 5-MeC content with 100 mg·L^-1Cr⁶⁺ treatment was lower than that of control seedlings, 5-MeC contents with the rest Cr⁶⁺ tested concentrations were still higher than that of control seedlings.四. Effect of Cr⁶⁺ on the PCD in wheat seedlings root tip cells. DNA Ladder was not examined with the conventional agarose gel electrophoresis in the shoots and roots DNA of wheat seedlings, which was possibly related to the few number of PCD cells. Chromium（VI）-induced PCD in root tip cells was only examined更多还原