Study On Salt Tolerance Mechanism At Seedling Stage And Salt Tolerance Gene Mapping

Salt stress seriously affects the growth of crops. Improving of the salt tolerance of crops is animportant stratergy to reduce the stress of crop production in Saline soil. Selection of salterant soybeangermplasm is important for salt tolerance mechanism study and breeding of salt tolerant soybeanvarieties. A simple and effective selection method is the foundation for the study of salt tolerance insoybean. In this study, by using representative salt toerant and sensitive soybean varieties, a simplemethod of identificating salt tolerant soybean at seedling stage was establised. The physiologicalmechanism was discussed through the grafting experiments and measuring of ion fluxs in root ofsoybean cultivars.Using the segregating F2:3family from a salt tolerant wild soybean NY36-87and saltsensitive soybean Peking, a new salt tolerantce gene was mapped on soybean chromosome18. The mainresults are as follows:1. Establishment of a simple method for identifying salt tolerant soybean at seedling stageUsed4salt tolerance varieties Tiefeng8, Wenfeng7, Suxianwandoutuan, Hartwig and4saltsensitive variets85-140, Peking, Zhonghuang39, Williams82, the seedlings grown in vermiculite weretreated with0,100,200, and250mM NaCl solutions for8days. It is easy to distinguish the salt tolerantand sensitive varieties based on foliar symptoms in both treatment of200and250mM NaCl treatmentand the SPAD value in salt sensitive varieties is lower than that in tolerant ones. Under250mM NaClstress, the Na~+content in leaves for salt-tolerant varieties was significantly lower than that ofsalt-sensitive varieties. There was a significantly negative correlation between Na~+content and SPADvalue in soybean varieties.2. Scion played an important role in Na~+transporting and salt tolerance of shoots in soybeanTo search for mechanism under the transporting Na~+, we examined regulation of Na~+content usinga reciprocal grafting technique. Six day old seedlings of two salt sensitive and two salt tolerant soybeancultivars were self-grafted or grafted to reciprocal rootstocks. Grafting itself limited Na~+transport toshoots. Na~+accumulation in root had no significant change in rootstocks regardless the salt tolerance ofscion. The increase of salt tolerance and significant decrease (52.7%-95.1%) of leaf Na~+content wereobserved in salt sensitive scions when grafted on salt tolerant rootstocks, with respect to theirself-grafted plants. When salt tolerance scions grafted on salt sensitive rootstocks, the increase of salttolerance and significant decrease (29.9%-75%) of leaf Na~+content were observed too. The studysuggests that Na~+exclusion by the salt tolerant soybean rootstocks is the major mechanism explain thedecreased in leaf Na~+content and increase salt tolerance of sensitive scions grafted on salt tolerancerootstocks. Scion played an important role in Na~+transporting and salt tolerance of shoots in soybean.3. Na~+/H~+antiporter is very importent in salt tolerant variety of Tiefeng8Increased H~+influx and K~+efflux were observed in both roots of salt tolerant variety Tiefeng8andsensitive one85-140after2days of NaCl stress. The influx of H~+was inhibited by toth H~+-ATPaseinhibitor vanadate and Na~+/H~+antiporter inhibitor amiloride treatment. Vanadate promoted K~+efflux, inhibited Na~+efflux. After exposer to100mM NaCl, the influx of H~+and efflux of K~+were increased byboth vanadate and amiloride in Tiefeng8other than85-140. These results indicated the Na~+/H~+antiporter plays an important role in salt tolerant variety Tiefeng8under salt stress.4. A salt tolerance gene was mapped on Chromosome18in wild soybean NY36-87The salt tolerant wild soybean NY36-87was crossed with salt sensitive variety Peking to make asegregant population. A F2:3family with220lines was screed for salt tolerance, the salt tolerance genesegregated with a ratio of1:2:1(tolerant: heterozygous: sensitive). BSA method was used to selectpolymorphic SSR markers. A new salt tolerance gene was mapped on soybean chromosome18in a240kb region between markers18-7and18-8.