Effect of short-term salt stress on the absorption of K+ and accumulation of Na+,K+ in seedlings of different wheat varieties

Salinity is a major abiotic stress affecting agricultural production.Salinity tolerance in glycophytes is mainly associated with the ability to maintain high K+:Na+ ratios in shoots.The ability of the plant to exclude uptake of sodium(Na+) and to retain potassium(K+) in the cells may contribute to this trait.To better understand the accumulation and transport of salinity ions in wheat under high-salt conditions,we examined responses of plant roots under saline conditions using three varieties of wheat with varying levels of salt tolerance;Chinese-Spring,ZhouYuan-9369,and ChangWu-134.We examined seedling growth,absorption of K+,and accumulation of both Na+ and K+ under salt stress.The non-invasive micro-test technique(NMT) was adapted to detect the K+ flux in the roots and to determine Na+ and K+ contents of shoots and roots after 2 days of salt stress.The advantages of the non-invasive micro-test technique over traditional methods are that it is rapid,non-invasive,and it can be used on live plants.For all varieties,the growth of wheat seedlings was inhibited by salt stress,and the salt-tolerant cultivar ChangWu-134 maintained higher dry weight than the other two varieties.In all three varieties,roots were more strongly inhibited than shoots under salt stress.The efflux velocity of K+ in roots was nearly 15 times greater in Chinese-Spring than in ChangWu-134 under saline conditions.This result was consistent with those obtained using traditional methods,which showed that the K+ contents in shoots and roots decreased under salt stress.During salt stress,the Na+ contents in shoots and roots increased while the K+ contents decreased,resulting in an increase in the Na+:K+ ratio.Among the three varieties,Changwu-134 showed the lowest concentration of Na + in cells of seedlings under salt stress.The Na+:K+ ratios in shoots and roots were higher in Chinese-Spring than in ChangWu-134,suggesting that the salt-tolerant cultivar ChangWu-134 showed greater Na+-exclusion capability than the salt-sensitive cultivar Chinese-Spring.More closely related indices of salinity tolerance have been proposed,such as Na+ and K+ concentrations and K+/Na+ tissue content ratios in shoots or roots,or the production of specific metabolites in various species.Among the three wheat varieties,the Na+ restriction capability was highest in Changwu-134.This indicates that Changwu-134 was able to increase accumulation of Na+ in the roots and decrease the transportation of Na+ to the shoots as mechanisms to tolerate salinity.Thus,improving the ability of plants to accumulate salinity ions and control their transport should produce cultivars with even greater salt tolerance.In conclusion,under salt stress,the significant increase in the velocity of K+ efflux and the accumulation of Na+ resulted in increased Na+:K+ ratios in roots and shoots.Moreover,the Na+:K+ ratio differed between salt-tolerant and salt-sensitive wheat cultivars.In wheat,it appears that the capacity to retain K+ is an important indicator of salt tolerance,and the non-invasive micro-test technique should be a reliable screening method to select salt-tolerant cultivars in plant breeding programs.