A Preliminary Study On The Effect Of Melatonin On Plant Salt Tolerance

Although melatonin(N-acetyl-5-methoxytryptamine)could allevaite salinity stress,how it improves salinity toxicity is still not fully characterized.In this study,we use rapeseed,Arabidiosis,and alfalfa as our experimental materials to have a preliminary study on the effect of melatonin on plant salt tolerance,the experimental results are as follows:1.Endogenous melatonin and thereafter nitric oxide(NO)accumulation was progressively increased in NaCl-stressed rapeseed(Brassica napus L.)seedling roots.Application of melatonin and NO-releasing compound not only counteract NaCl-induced seedling growth inhibition,but also reestablish redox and ion homeostasis,the latter of which are confirmed by the alleviation of reactive oxygen species overproduction,the decreases in thiobarbituric acid reactive substances production and Na+/K+ratio.Consistently,the related antioxidant defence genes/proteins,sodium hydrogen exchanger(NHX1),and Salt Overly Sensitive2(SOS2)transcripts are modulated.The involvement S-nitrosylation,a redox-based posttranslational modification triggered by NO,is also suggested.Furether resutls show that the concentration of NO is increased by the addition of melatonin in seedling roots subjected to NaCl.Above responses are abolised by the removal of NO production by NO scavenger.We further discovers that NO do not alter endogneous melatonin synthesis in roots supplemented with either melatonin or NaCl,thus excluding the possibility of NO-triggered melatonin prouduction.Genetic evidence reveals that,compared to the Arabidopsis wild-type,the hypersensitivity to NaCl in nial/2 and noal mutants(exhibiting null nitrate reductase activity and indirectly reduced endogenous NO level,respectively)can not be rescued by melatonin supplementation.This may be supported by the failure in reestablishing redox homeostasis and induction of SOS signaling.Together,by using a combination of pharmacological,molecular,and genetic approaches,we conclude that NO operates downstream of melatonin promoting salinity tolerance.2.Salt stress could induce the expression of MsSNAT and improve melatonin leve.Then.the MsSNAT was cloned and transferred to Arabidopsis.Experimental results showed that the salt tolerance of MsSNAT transgenic Arabidopsis was stronger than that of the wild-type,mainly showed in that the salt stress alleviated the growth of Arabidopsis roots and reduced salt stress on Arabidopsis chlorophyll damage,and the content of endogenous melatonin is higher than that of wild type.In conclusion,in pharmacology,molecular biology,and genetics experiments,we concluded that MsSNAT may be a key factor for plants responding to abiotic stress,which can regulate the synthesis of melatonin in plants.