Mechanism Of Interaction Between Hydrogen Sulfide And Abscisic Acid In Regulating Cucumber Phpotosynthetic Carbon Assimilation And Chilling Tolerance

Cucumber（Cucumis sativus L.）is one temperature-bias and chilling-sensitive plant.During the winter and spring seasons,cucumber plants often encounter low temperature stress and it has become the key factor which limits the growth,yield and quality of cucumber plants due to the poor control ability of solar-greenhouse conditions.As one endogenous gas signal molecule,hydrogen sulfide（H₂S）plays an important role in regulating plant growth and development as well as responding to abiotic stress.Meanwhile,abscisic acid（ABA）is also one significant signaling molecule involved in response to biotic and abiotic stresses of plants.However,it is still unclear the interactions between H₂S and ABA in controlling the photosynthetic carbon fixation and low temperature tolerance of cucumber.To study the effect of H₂S and ABA on photosynthesis,accumulation of active oxygen and antioxidant system and further to evaluate the mechanism of the interaction between H₂S and ABA in improving the photosynthetic carbon fixation and chilling resistance of cucumber,‘Jinyou 35’cucumber seedlings were used as the materials and treated by foliar-spraying sodium hydrosulfide（NaHS,the donor of H₂S）with the concentration as 1 mmol·L^-1,ABA with the concentration as 50μmol·L^-1,Hypotaurine（HT,the scavenger of H₂S）with the concentration as 0.15 mmol·L^-1,sodium tungstate（Na₂WO₄,the synthesis inhibitors of ABA）with the concentration as 3 mmol·L^-1,as well as the compounds of Na₂WO₄(3 mmol·L^-1)and NaHS(1 mmol·L^-1),and the compounds of HT(0.15 mmol·L^-1)and ABA(50μmol·L^-1),respectively,and deionized water as the control（CK）.The main results are as follows:1.After low temperature stress,the chilling injury index and electrolyte leakage of cucumber seedlings pre-treated by NaHS(1.0 mmol·L^-1)and ABA(50μmol·L^-1)decreased significantly.The endogenous H₂S and ABA were induced by chilling stress and ABA improved the activity of L-/D-cysteine desulfhydrase（L/DCD）and the gene relative expression to promote the production of endogenous H₂S.Also,ABA content elevated rapidly as a result of the increase of the activity of 9-cis-epoxycarotenoid dioxygenases（NCED）and the mRNA abundance raised by NaHS.2.Both H₂S and ABA significantly reduced the effect of chilling stress on the growth of cucumber seedlings.However,ABA synthesis inhibitors weakened the positive effect of NaHS on growth of cucumber seedlings,meanwhile,facilitating role induced by ABA could be reversed by HT which was the scavenger of H₂S.When Na₂WO₄ and HT were applied alone,both leaf area and daily increments of dry matter were obviously lower than those of water treatment,which suggested that there was a dialogue mechanism between H₂S and ABA signals under low temperature stress.3.NaHS and ABA increased the photosynthesis（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）,actual photochemical efficiency（ΦPSⅡ）and maximal photochemical efficiency of PSⅡ（Fv/Fm）and decreased intercellular CO₂ concentration（Ci）notably.Also,both the two treatments showed the clearly higher activities of ribulose-1,5-bisphosphatecarboxylase/oxygenase（Rubisco）,rubisco activase（RCA）,sedoheptulose-1,7-bisphosphatase（SBPase）,fructose-1,6-bisphosphatase（FBPase）,fructose-1,6-bisphosphate aldolase（FBA）and transketolase（TK）as well as the mRNA abundance than those of the control.The inhibition of ABA synthesis led to the decrease of promotive effect of H₂S on photosynthesis of cucumber seedlings under chilling stress and ABA showed the same results when H₂S was removed.Therefore,these data indicated that both H₂S and ABA relieved the effect of low temperature stress on photosynthesis of cucumber seedings and the interactive effect existed between the two signaling molecules.4.Under chilling stress,NaHS and ABA decreased the accumulation of active oxygen,while increased the activities of superoxide dismutase（SOD）,peroxidase（POD）,ascorbic acid oxidase（APX）and glutathione reductase（GR）and the gene expression as well as the contents of ascorbic acid（AsA）and glutathione（GSH）and the ratio of reduced/oxidized ascorbic acid（AsA/DHA）and reduced/oxidized glutathione（GSH/GSSG）in cucumber seedings,thus to reduce the peroxidation damage of low temperature stress to cucumber seedlings.The positive effect of H₂S on antioxidant ability of cucumber seedlings declined importantly when Na₂WO₄,one ABA synthesis inhibitor,was applied,meanwhile,HT,one H₂S scavenger,reversed the regulation of ABA on active oxygen in cucumber seedlings.The results showed that H₂S and ABA induced the chilling tolerance of cucumber seedlings and there were interactions and"dialogue"mechanisms in the process of signal transduction between the two signals.