Salt-tolerant Characteristics In Different Organs Of Polyploid Rice And Functional Analysis Of The OsDH Gene

High salinity is one of the most important environmental limiting factors of forage growth and productivity, as the high concentration of salt in soil causes ion imbalance, oxidative damage, water deficit and nutrient deficiency, which lead to molecular damage, growth retarded, and even death of plant,which could result in crop failures.Studies on salt tolerance mechanisms of plant and salt tolerance crops breeding have become to the focus issue within agricultural and biotechnological regions in recent years. Domestic and foreign scholars have researched the mechanism of the salt damage and tolerance in plant,and they have cloned a number of genes related to salt tolerance. Tested to verify,they have been harvested some transgenic plants which increased in salt tolerance.In this study, HN2026-2X, IIN2026-4X, Nippobare-2X and Nippobare-4X were selected and the salt stress concentration for evaluation of salt tolerance at germination period and early seedling stage in rice was studied.The objective of the present study are to elucidate the relationship between the polyploidy evolution and salt tolerance. The physiological and biochemical changes in shoots and roots of rice seedlings under the certain concentrations of salt stress were determined. Furthermore, We observed the change of the microscopic structure and ultrastructure of rice roots under NaCl stress,and determined the transcription levels of osDH gene in rice under NaCl stress.The main results are followings:(1) The germination rates were decreased significantly as the concentration of50mmol/LNaCl.The germination rate of HN2026-4X decreased from91.80%to81.57%after the salt treatment, while the germination potential from80.20%down to28.10%.(2) The height of the aerial parts, fresh weight, dry weight, leaf length, leaf width index of rice were decreased as the concentration of NaCl.Particularly,the concentrations of NaCl differed significantly between the diploid rice(HN2026-4X) and tetraploid rice(Nipponbare-4X).The growth of seedlings was inhibited while the shoot and leaf elongation of the tetraploid rice is often great less than diploid rice.(3) The inhibition rate of the HN2026-2X root length reached95.08%under the salt duress, while root fresh weight,dry weight,the number of root were all inhibited under salt stress. Acording to the root-top ratio, the shoot growth of Nipponbare-4X was inhibited more seriously than the root. Among them, the salt stress had minimal impact on HN2026-4X and had the greatest impact on HN2026-2X.(4) The Pro contents were increased both in shoot and root of all4kinds of rice seedings under the salt stress NaCl stress.The proline contentrice in the part of rice shoot is higher than the root,but the rate of change is less than the root after salt stress. After salt stress,Nipponbare-2X has the highest content of proline in the ground part, while the highest proline content of the root proline was in the rice of HN2026-2X.(5) There was a positive correlation between the content of free proline and soluble glucose and stress time under the150mmol/LNaCl.The content of soluble glucose in the roots of HN series increased significantly increased after salt stress while the difference in the roots of Nipponbare family were not obvious.(6) According to the observation of rice seedlings root anatomical structure under the salt stress, it was found that aerenchyma in roots of rice began to collapse which was dealing with3days under the150mmol/LNaCl, the collapse was more pronounced after5days, it can be observed compensatory thickening of the outer skin’s surrounding parenchyma cells. Phloem and xylem cells of the root center did not observe a significant change. Ultra structure can be observed under the electron microscopy that it caused the organelles and nucleus deformation cracking in the root cells under salt stress.(7) The quantiatative real time polymerase chain reaction(qRT-PCR) assay was developed to estimate the mRNA expression levels in the shoots and roots under3days and5days of salt stress.The resuts show that osDH gene expressions were increased significantly on rice seeblings in the shoots after the salt treatment. Among the four kinds of rice.the expression of osDH gene in the rice seedlings of Nipponbare-4X showed the highest level under3days and5days of salt stress in, the highest expression level in the roots were in the rice of HN2026-4X.