Mechanisms Of Plant Growth,Development And Response To Salt Stress Mediated By Plant Growth Regulators

Plant hormone with small molecules and large functions is an important endogenous factor in plant growth and development.Different plant hormones have different physiological functions.They form a huge network to finely regulate every stage of plant growth and development.Plant growth regulators,as synthetic substances,have similar functions to plant hormones and can regulate plant growth and development,which have been widely used in agricultural production.Among the plant growth regulators,there are three new plant growth regulators,alginate-derived oligosaccharide,chitosan oligosaccharide and coronatine widely exist in nature,with known and safe chemical composition and a great potential for promotion.Soybean(Glycine max)is native to East Asia,and it's an important food,oil and forage crop in the world.Due to the late start of research in the fields of germplasm collection,variety selection,and transgenic,coupled with the decrease of planting acreage,the increase in production cost and other factors,the contradiction between supply and demand of soybean is prominent,which is heavily dependent on imports.In recent years,China has vigorously promoted the intercropping of soybeans and other cultivation modes,which has increased the planting area of soybeans.However,due to the large gap existing in soybean production,it is still necessary to find more technical means to increase production and increase soybean production,so as to ensure the safety the national grain and oil security.As one of the most important abiotic stresses with global influence,salt stress can inhibit almost all development processes,such as inhibit seed germination,vegetative growth and reproductive growth,and affect the whole development process.In the past,scientists have studied the physiological changes and signaling pathways of plants in response to salt stress.It is worth noting that both salt stress and ABA treatment can induce the production of reactive oxygen species(ROS),and ABA signal transcription factor ABI4 can induce the production of ROS under salt stress.So,is there a relationship between these two biological processes?Through which active oxygen synthesis gene does ABI4 induce the production of active oxygen under salt stress?These problems are worthy of further study.In this thesis,soybean,an important grain and oil crop;and Arabidopsis(Arabidopsis thaliana),a model plant,were used as experimental materials through means of plant physiology,agronomy,genetics,molecular biology and biochemistry,to study the effects of new plant growth regulators,alginate-derived oligosaccharide,chitosan oligosaccharide and coronatine,on the emergence of seedlings in the field,and spraying three plant growth regulators on soybean leaves in the early stage of reproductive growth.Effects of water solution of plant growth regulator on sugar content,agronomic characters,yield characters and quality characters of soybean during development have been assessed.The effect of ABI4 mediated ROS production on seed germination under salt stress is also revealed.The results are summarized as follows:(I)Three plant growth regulators(alginate-derived oligosaccharide,chitosan oligosaccharide and coronatine)can improve the seedling rate of soybean in the field.The recommended dosage of three plant growth regulators for seed dressing was 100m L aqueous solution per kilogram of soybean seed with concentrations of 25 mg·L^-1,100 mg·L^-1 and 0.05 mg·L^-1,respectively.Among three plant growth regulators,the optimum concentration of alginate-derived oligosaccharide to promote the emergence of soybean seedlings in the field is the most obvious.Foliar spraying of three plant regulators can significantly improve the plant height,extremely significantly increase the stem diameter and 100 grain weight of soybean,improve the lodging resistance and yield of soybean;affect the number of soybean branches,among which alginate-derived oligosaccharide can promote soybean branches,chitosan oligosaccharide can inhibit soybean branches,low concentration of coronatine can promote soybean branches but high concentration has no effect;soybean crude protein content has significant statistical level with the increase,the crude fat content decreased significantly,but the change range was small,which had little effect on the actual production.Foliar spraying of plant regulators did not affect the germination of soybean seeds after harvest.The recommended dosage of alginate-derived oligosaccharide,chitosan oligosaccharide and coronatine for foliar spraying is 50g,50g and 0.01g per hectare.Compared with the best amount of foliar spray,the effect of alginate-derived oligosaccharide was the best to improve soybean yield.(II)Under salt stress,ABI4 promotes RbohD transcription by directly binding to the promoter,and inhibits the germination of seeds under salt stress by up-regulates the biosynthesis of ROS.abi4 and rbohd were insensitive to salt stress during seed germination.The expression of RbohD gene induced by salt stress was dependent on ABI4.Further biochemical analysis also showed that ABI4 interacted directly with RbohD promoter and promoted the production of ROS during seed imbibition,resulting in cell membrane damage and finally inhibited seed germination under salt stress.Similarly,genetic and physiological evidence showed that the lack of rbohd rescued to a large extent the salt sensitive phenotype of OE-ABI4(Overexpression-ABI4)seeds in the process of seed imbibition,and rbohd was able to rescued the production of hydrogen peroxide and superoxide anion in OE-ABI4 seeds under salt stress,and finally the low activity phenotype of OE-ABI4 seeds under salt stress.Therefore,ABI4 is regulating ROS synthesis,further reducing cell membrane integrity and seed vigor,and finally inhibiting seed germination under salt stress.In conclusion,three plant growth regulators,alginate-derived oligosaccharide,chitosan oligosaccharide and coronatine,have the potential to increase soybean yield in agricultural production;the transcription factor ABI4 mediates the expression of RbohD,and then inhibits seed germination under salt stress.