| Cucumber?Cucumis sativus L.?is a typical cold-sensitive vegetable that is commonly encounter chilling stress because they are mainly cultivated through the winter in solar greenhouses in the north of China.Low temperature has become an important factor affecting the growth,yield and quality of cucumber in solar greenhouse.As signaling molecules,both salicylic acid?SA?and hydrogen sulfide?H2S?play important roles in the regulation of plant growth and development,and response to abiotic stress.However,the synergy of SA and H2S regulates photosynthesis under chilling stress is still unclear.Here,we used‘Jinyou 35'seedlings to study the relationship between SA and H2S in regulating the chilling tolerance.Seedlings were foliar sprayed sodium sulfide?NaHS,H2S donor?,SA and there scavenger or biosynthesis inhibitor.The H2O pretreatment at room temperature was used as the control.The main results are as follows:1.Both SA and H2S are induced by low temperature.SA increased the L-/D-cysteine desulfhydrase?L-/D-CD?activity and relative mRNA expression,and consequently promoted the endogenous H2S production.However,NaHS had little effect on the activity of phenylalnine ammonialyase?PAL?,benzoate-2-hydroxylase?BA2H?,and isochorismate?ICS?and isobranchoatelyase?IPL?,as well as the PAL and ICS mRNA expression and endogenous H2S level.2.SA-and NaHS-treated seedlings showed significant decreases in electrolyte leakage rate?EL?,malondialdehyde?MDA?content,and the accumulation of hydrogen peroxide?H2O2?and superoxide anion?O2.-?.However,SA and NaHS increased the activities of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?,ascorbate peroxidase?APX?and glutathione reductase?GR?,as well as the reduced/oxidized glutathione?GSH/GSSG?and reduced/oxidized ascorbic acid?AsA/DHA?.The seedlings treated with SA and NaHS revealed lesser damage symptoms caused by chilling stress.These data suggested that SA and H2S alleviated the negative effects of chilling stress on the chilling induced membrane lipid peroxidation injury by regulating the antioxidant enzyme's activity and mRNA expression,and redox state of glutathione and ascorbic acid in cucumber seedlings.The SA-induced higher chilling tolerance in cucumber seedlings were suppressed by application of the H2S scavenger hypotaurine?HT?.However,the H2S-induced adaptive response to chilling stress was not markedly affected by SA biosynthesis inhibitor paclobutrazol?PAC?and2-aminoindan-2-phosphonic acid?AIP?.3.Low temperature led to up-regulating in the expression of c-repeat binding factor?CBF1?,inducer of CBF expression?ICE?and cold responsive?COR?genes in cucumber seedlings.Compared with the H2O treatment,SA,NaHS,HT+SA,PAC+NaHS and AIP+NaHS treatments showed significantly higher up-regulation degree in cold responsive genes in cucumber.The expression of cold responsive genes were lower in HT+SA-treated seedlings than in SA-treated seedlings,whereas,no differences were observed in cold responsive genes'expression between PAC+NaHS or AIP+NaHS and NaHS-treated seedlings.These results suggest that H2S locates downstream of SA regulate chilling tolerance in cucumber seedlings.4.SA-and NaHS-treated seedlings showed increases in the photosynthetic rate?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?,while a decrease in intercellular CO2concentration?Ci?,compared with the H2O-treated seedlings.SA and NaHS also increased the CO2 assimilation,which mainly attributed to an increase in the activity and gene expression of the ribulose-1,5-bisphosphate carboxylase?RuBPCase?,rubisco activase?RCA?,sedoheptulose-1,7-bisphosphatase?SBPase?and fructose-1,6-bisphosphatase?FBA?.Meanwhile,SA and NaHS improved the actual photochemical efficiency(?PSII)and maximal photochemical efficiency?Fv/Fm?of PSII,therefore alleviated the damage in photosynthetic apparatus and influence in growth caused by chilling stress in cucumber seedlings.The SA-induced higher photosynthesis and growth in chilling stressed seedlings were suppressed by addition of HT.However,the H2S-induced adaptive response of photosynthesis and growth to chilling stress was not markedly affected by PAC and AIP.These data suggest that H2S function as a downstream signal for SA-induced photosynthesis in cucumber seedlings under chilling. |
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