Physiological And Biochemical Mechanism Of Sucrose Metabolism As Affected By IAA In Cotton (G.hirsutum)

Cotton is an important global fiber crop,and the main breeding objective has been to improve fiber production and quality.As important signal regulatory factors,plant hormones play an important role in all stages of cotton development.IF11 plant material was used in this experiment.There was increased auxin content at initial fiber development stage while fiber production and quality showed different degrees of improvement.Sucrose not only acts as an important intermediate transition product in the process of cellulose synthesis,but also can be used as a signal-regulating molecule to influence sucrose metabolism and change related enzyme activities during cotton fiber development.This in turn affects the synthesis of cellulose and ultimately affects the yield and quality of cotton fiber.In this study,20 mg·L-1 of exogenous IAA solution was used to induce TM-1 and JM14.Combined with the specific higher IAA content of IF11,an investigation of the effects of IAA and sucrose content on the germination,seedling growth,leaf photosynthesis,cotton fiber development and its yield as well as quality in a specific period was carried out.The relationship between the dynamic changes of IAA content and sucrose metabolism were also explored.More in-depth study of IAA and sucrose metabolism in the cotton fiber development process provided a theoretical basis of their role in cotton fiber production and quality improvement.The main results are as follows:（1）In this study,we compared other methods for the determination of plant hormones（Gibberellin,auxin and abscisic acid）and soluble sugars（fructose,glucose and sucrose）.This required accuracy of the test results from improved sample extraction methods and chromatographic conditions for the establishment of an optimized rapid determination of hormone and soluble sugar content through HPLC and determination of the corresponding standard curve.The regression curve R2values were above 0.999,showing a good linear relationship.（2）Cotton seed induced by 20 mg·L^-1 exogenous auxin was mainly used to research changes in contents of carbohydrates such as fructose,glucose and sucrose as well as in activities of enzymes related to sucrose metabolism such as acid invertase,neutral invertase,sucrose phosphate synthetase and sucrose synthase in buds and leaves at germination,seedling and flowering stage.The results showed that cotton seeds after exogenous IAA priming had higher IAA content than those after water priming at germination and seedling stage which significantly promoted seed germination,shortened average germination time and increased seedling biomass and leaf photosynthetic rate.In addition,both contents of the carbohydrates fructose,glucose and sucrose,and enzyme activities related to sucrose metabolism such as acid invertase,neutral invertase,sucrose phosphate synthase and sucrose synthase were also increased.However the photosynthetic rate,carbohydrate content and enzyme activity related to sucrose metabolism were not significantly affected.Therefore,it can be concluded that IAA priming mainly exerts influence at germination and seedling stage,but not at mid to late stage of cotton development.IAA might be involved in the regulation of carbohydrate and enzyme activities related to sucrose metabolism.（3）Through studying the changes in hormone and sugar content,photosynthetic rate as well as activities of enzymes related to sucrose metabolism in leaf,ovule and fiber at seedling and flowering stage of IF11,JM14 and TM-1.The results showed that auxin content in ovule of IF11 was significantly higher than that of JM14 and TM-1 between 0-5 DPA due to iaa M gene,thus significantly promoting the initial development of cotton fiber.In addition,carbohydrate content（fructose,glucose and sucrose）and enzyme activities related to sucrose metabolism（acid invertase,neutral invertase,sucrose phosphate synthase and sucrose synthase）were also increased,and the fiber quality and yield were improved to some extent.At the same time,it was also found that photosynthesis increased correspondingly at flowering stage,but no significant effect on photosynthetic rate,soluble sugar content and enzyme activities related to sucrose metabolism were observed during seedling stage.Lastly,through the changes of sugar content during fiber and seed development,it was found that there existed some competition for carbon between fiber and seed.