| Plants often suffer from many kinds of stress conditions. Every year, disaster in the world made sever decrease of crop production and affect the quality of farm products. Researches on the response of plant to stress and discover the cellular and physiological mechanism of plants in defending against different stress conditions will be helpful not only to understand the normal physiological process completely but also to improve the productive potentialities of crops and protect the environment, which is always an important content in plant science.In order to discover the mechanism in plant defending against stress conditions, a differential display method was used to isolate genes regulated by stress condition in rice and tobacco, and the expression pattern of these genes in different stress conditions was investigated. Transgenic tobacco plants were used to analyze the function of plant glutathione S-transferase (GST) in defending against oxidative stress. The detailed work was as follows:1 An improved differential display method was used to identify ethephon-regulated genes from tobacco. Total 24 cDNA fragments expressing differently between control and ethephon-treated plants were isolated. In the 17 fragments that were identified by dot hybridization to be truly positive results, 12 of them were induced by ethephon and 5 were inhibited. Sequence analysis and BLAST analysis in the GenBank database indicated that the 12 fragments induced by ethephon were some stress and PCD-related genes, hormone-related genes or cell wall-related genes. Five of them represent for novel genes, and one full length cDNA were amplified by RACE method. The other 5 genes inhibited by ethephon were proved to be photosynthesis-related protein genes, which indicated that there is a tight relationship between ethylene and photosynthesis in plant. In order to explore the relationship of these ethephon-induced genes with stress. RT-PCR analysis of these genes in different stress conditions were carried out. and the putative function of these genes in stress werediscussed.2 A differential display method was used to identify oxidative stress-regulated genes from rice, and 4 truly positive fragments were obtained by this way. Two of them got enhanced expression by oxidative stress treatment, sequence analysis revealed that they present function unknown genes, encoding a glutathione transporter (GT1) protein and a C terminal binding protein (CtBP) respectively. The other two gene fragments were oxidative down-regulated, and sequence analysis indicated that they share high similarity with two known genes in rice. In order to explore the function of these genes in defending against stress conditions, Northern blot analysis were used to analyze the expression pattern of these genes in different stress conditions and the treatment of stress signal molecular (SA. ABA, ethylene), the role played by these genes in differential stress conditions were discussed.3 A glutathione S-transferase (GST) gene from cotton was introduced into tobacco by Agrobacturium-mediated leaf disk transformation method. Southern blot analysis of the transgenie plants indicated that the foreign GST gene has introduced into the tobacco genome. It's also suggested that there are many copy of GST genes in tobacco genome. By the enzyme activity and northern blot analysis, 3 transgenie tobacco plants exhibited high expression level of foreign GST gene were selected to treat with MV inducted oxidative stress. The ion leakage results indicated that transgenie plants overexprcssing foreign GST show high resistance to oxidative stress. Enzyme activity of six antioxidate enzymes (GST, glutathione peroxidase. ascorbate peroxidase, catalase, superoxide dismutase. peroxidase) in control and transgenie plants were monitored during MV treatment. The activity change models of these enzymes were compared between control and transgenie plants.
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