| Muskmelon is an important fruit-type vegetable crop which widely cultivated in China,and a slight acidic soil condition is suitable for its growth.In recent years,due to the unreasonable use of chemical fertilizers and other problems,the soil salinity problem has become increasingly prominent,which seriously affects the normal growth and development of muskmelon and reduces yield and quality.Therefore,it has a great scientific and practical significance to explore ways to reduce the damage caused by salinity-alkalinity stress in muskmelon.γ-Aminobutyric acid(GABA)is an exogenous substance that can effectively reduce the damage of abiotic stress on crops.At present,it is not clear about the signal molecules and their regulatory pathways involved in GABA mitigating the salinity-alkalinity stress of muskmelon.Therefore,in this paper,muskmelon(Cucumis melon L.cv.Yipintianxia No.208)was used as a test material to study the effects of exogenous GABA on the metabolism of polyamines(PAs)and nitric oxide(NO)synthesis in muskmelon leaves,and fruit quality of muskmelon under salinity-alkalinity stress;And the role of PAs and NO in GABA-regulated salinity-alkalinity tolerance of muskmelon.The main results obtained were as follows:1. Salinity-alkalinity stress inhibited the growth of muskmelon seedlings,resulting in excessive Na~+accumulation and K~+outflow,and the number of autophagosomes in muskmelon leaves increased;While exogenous spraying of GABA can significantly reduce the Na~+/K~+ratio,increase the content of Fe element,further increase the number of autophagosomes in muskmelon leaves,and alleviate the inhibition of salinity-alkalinity on muskmelon growth.2. PAs are involved in GABA-regulated Na~+/K~+homeostasis and membrane lipid peroxidation.Under salinity-alkalinity stress,GABA pretreatment significantly increased the contents of free putrescine(Put),spermidine(Spd),spermine(Spm),arginine(Arg)and methionine(Met)in muskmelon leaves,and up-regulated genes related to PAs[(arginine decarboxylase(ADC),N-carbamyl putrescine hydrolase(CPA)and Spm synthetase(SPMS),S-adenosylmethionine decarboxylase(SAMDC)];Exogenous Spd reduced the inhibition of salinity-alkalinity stress on muskmelon growth,relative conductivity(REC),malondialdehyde(MDA)content and Na~+/K~+ratio.Pretreatment with the Dicyclohexylamine(Spd synthesis inhibitor dicyclohexylamine,DCHA)could eliminate GABA-regulated ion homeostasis,membrane peroxidative damage,and plants growth.In conclusion,under salinity-alkalinity stress conditions,GABA promotes the synthesis of PAs,which participates in the GABA-regulated membrane lipid peroxidation and Na~+/K~+homeostasis,thereby improving the resistance of muskmelon to salinity-alkalinity stress.3. NO is involved in GABA-mediated Na~+/K~+homeostasis and membrane lipid peroxidation.Salinity-alkalinity stress caused a rapid increase of endogenous NO levels in muskmelon leaves.Under salinity-alkalinity conditions,GABA pretreatment can increase NO content and the activities of nitrate reductase(NR)and nitric oxide synthase(NOS);the gene expression level of NR was up-regulated,and the expression level of NOS was down-regulated.The application of exogenous sodium nitroprusside(SNP,NO donor)weakened the inhibition of muskmelon growth by salinity-alkalinity stress,reduced MDA content,REC value and Na~+/K~+ratio;In contrast,the application of c PTIO(NO scavenger)can reverse the beneficial regulation from GABA-reduced membrane peroxidation damage,ion homeostasis,and muskmelon seedling growth.In summary,salinity-alkalinity stress induced a significant increase in NO levels,and the increased NO was involved in the GABA-mediated Na~+/K~+homeostasis to reduce membrane lipid peroxidation damage,and this increased salinity-alkalinity tolerance of muskmelon.4. GABA can affect the quality of muskmelon fruits,and spraying GABA can improve the quality of muskmelon fruits by adjusting the total soluble sugar and nitrate nitrogen content of muskmelon under salinity-alkalinity. |
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