| Cotton is one of the most important economic crops in the world. It is also the largest natural fiber crop and the world's sixth oil crop. More than 90 percent of cotton value exists in fiber and its fiber is the major raw material used for textile industry, so cotton holds an important place in national economy and human life. With rapid development of textile technology and the increasing demand of the citizens for higher quality of textile products, it is urgent to improve cotton fiber quality. The cotton with long fiber, high regularity, uniformity and modest strength satisfies better with the demand of production and life. Because there is a genetically negative correlation between the yield and the quality of cotton, it is difficult to improve fiber yield and quality simultaneously through traditional breeding techniques. Along with the improvement in genetic engineering of plant breeding, it is promising to employing to these techniques to improve fiber quality.Plant hormones play an important role in plant growth and development. Slight changes of hormone levels will influence plant growth. IAA is an important plant hormone for plant growth and development. Researches have suggested that IAA takes a vital role in fiber initiation and elongation. But there is short of genetic evidence to support these results. To further determine the effects of the change of internal IAA content in cotton seed coat or fiber on fiber development, an indoleacetic acid-lysine synthetase (iaaL), which could decrease the endogenous IAA content by converting IAA to IAA-lysine, was studied in the experiment. The iaaL gene under the control of E6 or FBP7 promoter was introduced into cotton genome via Agrobacterium-mediated transformation. The change of endogenous IAA level and its effects on the number and quality of cotton fiber in transgenetic cotton lines were carefully studied.The main results are as follows:1. Via Agrobacterium-mediated method, 20 E6::iaaL transgenic cotton plants were obtained. Southern Blot confirms that a single copy of iaaL was integrated in all the E6::iaaL transgenic plants.2. According to the expression level of iaaL gene in E6::iaaL transgenic plants by RT-PCR analysis, two independent transgenic lines were chosen for further study.3. Fiber measurement in To generation of E6::iaaL transgenic plant showed that the fiber length of transgenic plants was shorter than controls. The length of transgenic plants was 24.03mm or 25.83mm, and that of the controls was 30.77mm.4. The fiber initiation on Odpa-ovule was illustrated by scanning electron microscope. Results showed that no significant difference was found in the number of fiber initials between E6::iaaL transgenic plant and wild-type plant. However in FBP7::iaaL transgenic plant, we found the number of the fiber initials was lower than that of wild-type plant.5. The number of mature cotton fibers in E6::iaaL transgenic plants is lower than that of control. Compared to the wild-type plants, the number of mature fibers in E6::iaaL transgenic plants decreased by at lease 20%.6. Fiber strength of E6:: iaaL transgenic plants was reduced at a certain extent.The paper indicates that the expression of iaaL in fiber may inhibit the fiber initiation and elongation.
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