Study On Adaptation Mechanism Of Cotton Seedlings Roots In Floating Nursing Seedling(FNS)

Cotton is the woody dicotyledonous plant grown in upland soil. Traditionally, the cotton nursing seedling depended on xeric environment nursing seedling. At the beginning of this century, Chen Jin-xiang from Hunan agricultural university created a new cotton nursing seedling technology of aquatic environment- Floating nursing seeding(FNS). Compared with traditional xeric nursing seeding (nutrition bowl nursing seedling), seedling of FNS emerge more quickly, grow more orderly and more strongly, roots in nutrient solution grow more vigorously with healthy main root and more rootlets, the survival rate after transplanting seedling is higher, recovering time is shorter. But how did cotton seedling roots in FNS adapt to the aquatic environment? The difference of roots morphology structure and physiological and biochemical metabolism between xeric and FNS seedling was not clear, which hindered the nursing seedling technology popularization and application. Therefore, this paper attempted to study on seedling root structure, proteomics and key gene expression, to clarify aquatic adaptation mechanism of cotton seedling roots which would provide theoretical basis for the popularization and application of FNS and remove the understanding obstacle. Different varieties of cotton seedling growth status in FNS were analyzed using conventional method and WinRHIZO roots scanning system, and classified into different groups through principal component analysis and cluster analysis. Among different cotton varieties, the CCRI 12 as the most suitable variety to FNS was chosen as research material. With the control of the matrix moisture seedling method, ultrastructure and microstructure of main root tip of cotton seedling coming from FNS at different seedling stages were observed by transmission electron microscope and optical microscope. Protein difference between the control and aquatic root at the 3-leaf and 1-heart stage in FNS was analyzed using two-dimensional electrophoresis analysis. The expression of four key genes including phosphoglycerate kinase gene, enolase gene, alcohol dehydrogenase gene and 14-3-3b gene of cotton seedling roots, stem, leaves in FNS were analyzed by real-time fluorescence quantitative PCR technology. According to the adaptive ability of different cotton varieties in FNS,29 cotton cultivars were divided into three groups:high adaptation, medium adaptation and no adaptation. In Floating nursing seeding (FNS), main root of cotton seedling was found with appearance of aerenchyma, while the control did not appear. Comparing with control, the cortical parenchyma cells of main root in FNS were smaller, and the growth of the xylem was weaker. Especially, the conduit diameter and the ratio of the conduit in stele were significantly smaller than the control. For tip cells of main root in FNS, there was phenol material at the 1-leaf and 1-heart stage, cortical cell gap at the 2-leaf and 1-heart stage, starch grain at the 3-leaf and 1-heart stage, and crystal cells with plasmolysis in the 4-leaf and 1-heart stage. As the protein two-dimensional electrophoresis results of of aquatic roots and control roots at the 3-leaf and 1-heart stage, there were 28 differentially expressed proteins including 20 non-redundant proteins. Protein functional classification indicated that these proteins were related with metabolism, cell structure, cell defense, energy metabolism, protein synthesis and cell growth, and mainly involved in metabolic pathway including glycolysis, ethanol fermentation, and tricarboxylic acid cycle. The relative expression of phosphoglycerate kinase gene of aquatic roots in FNS was higher than control from the 2-leaf and 1-heart stage to the 4-leaf and 1-heart stage, with the increase trend from the 1-leaf and 1-heart stage to the 4-leaf and 1-heart stage and the decrease trend from the 4-leaf and 1-heart stage to the 5-leaf and 1-heart stage. The relative expression of enolase gene of aquatic root in FNS with the decrease trend from the 1-leaf and 1-heart stage to the 4-leaf and 1-heart stage was higher than the control with the unchanged trend. The relative expression of alcohol dehydrogenase 2a gene of aquatic root in FNS was higher than the control from the 2-leaf and 1-heart stage to the 5-leaf and 1-heart stage with the increase trend from the 1-leaf and 1-heart stage to the 4-leaf and 1-heart stage and the decrease trend from the 4-leaf and 1-heart stage to the 5-leaf and 1-heart stage. The relative expression of 14-3-3b gene of aquatic root in FNS with the decrease trend from the 1-leaf and 1-heart stage to the 5-leaf and 1-heart stage, were less than the control with significantly different at every stage. In FNS environment, different cotton varieties showed the difference adaptive ability. The difference was mainly shown in the roots external form and its internal structure. Cotton seedling aquatic roots induced by FNS were adapted to aquatic environment through the changes of tissue and cell structure. At the same time, the physiological and biochemical metabolism also appeared obvious difference, aquatic roots could be regulated the metabolic pathway in order to adapt to the aquatic environment through specific gene and protein expression.