Effect Of Exogenous NO On The Growth And Polyamine Metabolism Of Cucumber Seedlings Under Low Temperature Stress

Cucumbers,low-temperature-sensitive plants,are widely cultivated as commercial crop is greenhouses.It is susceptible to low temperature damage during the growth and development of cucumber,such as cold spring.Previous studies have found that nitric oxide(NO)can not only regulates plant growth,but also participates in the regulation of plant abiotic stress as a signal molecule.In this study,"Jin Yan NO.4" cucumber seedlings were used for experimental material.Cucumber seedlings with different NO levels were constructed by chemical genetic methods.The effects of NO on growth,development and low-temperature tolerance of cucumber seedlings under normal conditions and low temperature(10?/6?)stress were studied.The main results are as follows.1.When the first true leaves of cucumber seedlings grew to the size of a one-d.ollar coin plants with different levels of NO began to be constructed.Under normal conditions,SNP(Sodium nitioprusside,a donor of NO)significantly increased the leaf area,fresh and dry weight,chlorophyll content,expression levels of chlorophyll synthesis genes FeCH and MgCH,and brassinolide synthesis gene DWF4 of cucumber seedlings when compared with CK.However,PTIO(NO scavenger)significantly inhibited the effects of NO.In addition,PTIO combined with SNP treatment also significantly increased the leaf area,dry and fresh weight,and chlorophyll content of cucmnber seedlings,indicating that the inhibitory effect of PTIO on cucomber can be partly restored by exogenous SNP.2.The characteristics of cucumber seedlings with different levels of NO were diffexent after low temperature stress.Compared with the CK,exogenous NO significantly increased endogenous NO content,NOS acivity chlorophyll content ard expression levels of genes related to synthesis,and significantly reduced malondialdehyde(MDA)content under low temperature stress.In addition,both SNP and PTIO treatments significantly increased the content of hydrogen peroxide(H2O2)after low temperature 24 h.PTIO combined with SNP treatment also significantly increased NO content,NOS activity,chlorophyll content and its related gene expression levels and inhibited MDA content.3.There are differences in polyamine synthesis in cucumber seedllings with different NO levels.Compared w ith CK,exogenous NO significantly incrasd the content of putrescine(Put)and spermidine(Spd),and up-regulated the expression levels of ADC,DAO,Cucsa.285950 under normal condition.However,PTIO significantly reduced the content of Put and Spd when compared with CK.PTIO combined with SNP treatment can obviously eliminate the inhibitory effect of PTIO by up-regulating the expressi on levels of ADC,DAO,Cucsa,285950 gene.NO significantly increased the content of Put,Spd and spermine(Spm)at 3 h and 6 h of low temperature.The expression levels of ADC,DAO,and Cucsa.285950 were significantly improved by NO at 6 h of low temperature stress.However,the expression level of SAMDC was always suppressed.Compared with CK NO significantly increased the content of Put,Spd and Spm,and significantly increased the expression level of SAMDC unnder low temperature 2.4 h and 48 h.However,PTIO reduced the levels of polyamines by inhibiting the expression levels of ADC DAO Cucsa.285950 after low temperature 24 h and 48h.PTIO combined with SNP treatment can also increase polyamine contenr,proving that the inhibitory effect of PTIO on polyamines can be partly eliminated by applying NO.4.The gene expression levels of cold-resistant transcription factors WRKY DWF4 and ICE in cucumber seedlings with different NO levels were different under low temperature stress.Compared with CK,SNP significantly up-regulated the expression levels of CsWRKY40(except low temperature 48 h).CsWRKY57,and ICE at24 h and 48 h of low temperature stress.In addition,SNP treatment significantly down-regulated the expression levels of CsWRKY53 and DWF4 genes that were negatively related to low temperature stress after low temperature 24 h and 48 h.However.PTIO had no effect on the expression levels of CsWRKY40,CsWRKY53,CsWRKY57 after low temperature 24 h.PTIO also had no effect on the expression level of ICE,and significantly increased the expression level of DWF4 during the whole stress period.