Effects Of Brassinolide On Physio-biochemical Characteristics And Genes Expression Of Cotton Under Drought Stress

As a pioneer crop to resist stress-tolerant, cotton is nearly 2,000 acres in Xinjiang.Along with the raised area of cotton acreage, adequate supplies of water has been become a serious bottleneck. Drought directly affect the expansion of acreage and increase of production of cotton, it has become a limiting factors of cotton production.As one of newly plant sterols hormone, Brassinosteroid is a broad-spectrum efficient in plant grow and develop, and enhances the resistance of stress, the length of cotton fiber and the leaf angle. Now, the main method of study in BR biological function was exogenous spraying, soaking, adding to media and others, and some of them has been used in agricultural industry. Soaking with BR can effectively improve seed germination under stress, while applying exogenous BR also can improve plant photosynthetic capacity, enhance antioxidant enzyme activity, promote water use efficiency and reduce the extent of membrane damage and other ways to ease the salt,drought, high temperature, disease and other stress on plant damage.Upland cotton(Gossypium hirsutum L.) cultivars “XLZ17” is a main cotton cultivar in Xinjiang, early maturity and good yield traits prominent features. In this study, using “XLZ17” as plant materials to investigate the effects of different concentrations of EBR on seed germination and seeding growth under iso-osmotic drought and salt stress, on “XLZ17”resist drought stress, on the gene expression of BR signaling pathway, the main results are as follows:1. To investigate the effects of brassinolide on seed germination and seeding growth under iso-drought and salt stress, the seed of upland cotton cultivars “XLZ17” soaked with 24-epibrassinolide(EBR) was used to analyze the regulative effects of brassinolide. The results showed that:(1) The enhanced effect of the germination rate and index of cotton seed, and root length, proline content, osmotic potential of cotton seedlings under iso-Na Cl stress were almost equal to iso-PEG stress after soaking0.25mg/L EBR;(2) 0.25mg/L EBR enhanced the germination percentage and vigor index of seeds, the relative water content of seedling, CAT, SOD activity; and kept low level of MDA, O2- under iso-Na Cl stress larger than iso-PEG stress;(3) while0.25mg/L EBR promoted the degree of the relative water content of root and POD activity under iso-Na Cl stress were smaller than iso-PEG stress. Under iso-Na Cl and PEG stress, different concentrations of EBR soaking promoting cotton growing indicators was vary. It will help to improve the seedling growth of cotton in arid saline alkali soil.2. The aim of this research was to illuminate the effects of exogenous EBR on the seedling growth under drought stress. The results showed that 0.5 mg/L EBR significantly promoted the plant growth, increased the levels of As A, GSH; soluble protein, betaine and proline; the activities of SOD, CAT, and POD; the contents of Chlorophyll a, b, a+b, improving the overall activity of the blades; while significantly decreased osmotic potential, MDA, O2-and H2O2 content, relative conductivity;moreover it advanced genes expression about BR and JMT synthesis, BR signaling pathways downstream. The results clarified that EBR could increase antioxidant enzymatic activities, antioxidants, cell growth, water transportation, and contents of osmotic adjustment substances, keeping low ROS contents, to relieve the harm of drought stress on cotton seedlings and enhance the resistance to drought stress.3. The full length c DNA of “XLZ17” BES1 gene was cloned by using homologous sequence cloning method: Gh BES1(Gen Bank accession number KP272000) contains an open reading frame(ORF) of 960 bp, which has 319 amino acids.Phylogenetic tree analysis indicated that Gh BES1 was closer to the Gossypium arboreum and Gossypium raimondii. Real time quantitative PCR results showed that the expression of Gh BES1 gene was rapidly up-regulated by drought and EBR, which was 4.2-fold and 2.3-fold of that of the respective controls under drought stress; when spary with EBR the expression of Gh BES1 gene reached the highest level at 3 h and 12 h, and about 4.2-times and 2.3-times of the controls, respectively. We constructed a binary plant expression vector p CEN2300-Gh BES1, then transformed into Nicotiana tabaccum plant by Agrobacterium-mediated leaf-disk method, and had obtained 20 T0 generation tobacco; moreover we have constructed virus-induced gene silencing vectors p TRV-Gh BES1, these laid a basis for futher clarifying the roles of Gh BES1 though over and silencing expression.