外源H_2S通过减轻低温光抑制增强黄瓜幼苗耐冷性

Hydrogen sulfide promotes chilling tolerance of cucumber seedlings by alleviating low-temperature photoinhibition

以‘津优3号’黄瓜(Cucumis sativus)为试材,叶面喷施硫化氢(H_2S)供体硫氢化钠(NaHS)、H_2S合成抑制剂氨氧基乙酸(AOA)、清除剂次牛磺酸(HT)或去离子水(对照),研究H_2S对低温下黄瓜幼苗光合作用和抗氧化系统的影响。结果表明:低温胁迫初期,黄瓜幼苗叶片的内源H_2S与L-/D-半胱氨酸脱巯基酶(L/DCD)活性快速升高,4或6 h后降低。随着低温胁迫时间的延长,黄瓜幼苗的丙二醛(MDA)含量、电解质渗漏率(EL)和冷害指数逐渐增加,NaHS处理的增加幅度明显小于对照,而AOA和HT处理的与对照差异不显著。低温下黄瓜幼苗的净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、光下光系统Ⅱ(PSⅡ)实际光化学效率(Φ_(PSⅡ))和暗下PSⅡ最大光化学效率(F_v/F_m),以及核酮糖-1,5-二磷酸羧化酶(RuBPCase)和果糖-1,6-二磷酸酯酶(FBPase)活性逐渐降低,胞间CO_2浓度(C_i)和初始荧光(F_o)趋于升高。与对照相比,NaHS处理的P_n、G_s、T_r、RuBPCase和FBPase活性,以及Φ_(PSⅡ)和F_v/F_m均较高,C_i和F_o较低,而AOA和HT处理的气体交换参数、光合酶活性及荧光参数多与对照差异不显著。随着低温胁迫时间的延长,黄瓜幼苗的过氧化物酶(POD)活性逐渐增加,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性,以及还原型谷胱甘肽(GSH)和抗坏血酸(AsA)含量先升高,后降低。NaHS处理的SOD、POD、CAT、APX和GR活性及GSH和AsA含量明显高于对照,AOA和HT处理的低于对照或与对照差异不显著。由此可见,H_2S受低温胁迫诱导,外源H_2S可通过减轻低温光抑制增强黄瓜幼苗耐冷性。

We investigated the response of hydrogen sulfide（H_2S）to chilling stress in‘Jinyou 3’cucumber（Cucumis sativus）seedlings.Simultaneously,we researched the effect of foliar spray with sodium hydrosulfide（Na HS,the donor of H_2S）,aminooxy acetic acid（AOA,H_2S inhibitor）and hypotaurine（HT,H_2S scavenger）on the photosynthesis and antioxidant system in cucumber seedlings,using deionized water-treated seedlings as the control.We found that the H_2S content and L-/D-cysteine desulfhydrase（L/DCD）activities increased during the first 4 or 6 h of chilling stress,but subsequently decreased.We also noticed that the malondialdehyde（MDA）content,electrolyte leakage（EL）and chilling injury index increased with chilling stress days.Na HS-treated seedlings decreased MDA content,EL and chilling injury index under chilling stress.However,there were no significant differences in the above parameters among the seedlings treated with AOA,HT and the control.Chilling stress led to a decrease in net photosynthetic rate（P_n）,stomatal conductance（G_s）,transpiration rate（T_r）,actual photochemical efficiency of PSⅡ（Φ_（PSⅡ））and maximum photochemical efficiency of PSⅡ in darkness（F_v/F_m）,while an increase in intercellular CO_2 concentration（C_i）and initial fluorescence（F_o）.Chilling stress also caused a decrease in activities of ribulose-1,5-bisphosphate carboxylase（RuBPCase）and fructose-1,6-bisphosphatase（FBPase）.NaHS-treated seedlings showed higher P_n,G_s,T_r,Φ_（PSⅡ）,F_v/F_m and activities of Ru BPCase and FBPase,whereas lower C_i and F_o compared with the control under chilling stress.No significant differences were found in the gas exchange,activities of photosynthetic enzymes and fluorescence parameters between AOA or HT treatment and the control.The peroxidase（POD）activity in cucumber seedlings increased gradually during chilling stress days.The activities of superoxide dismutase（SOD）,catalase（CAT）,ascorbate peroxidase（APX）and glutathione reductase（GR）,as well as the contents of reduced glutathione（GSH）and ascorbic acid（AsA）increased in the early days of chilling stress,but subsequently decreased.Compared with the control,NaHS-treated seedlings revealed a significant increase in activities of SOD,POD,CAT,APX and GR,and the contents of GSH and AsA.However,there were no significant differences in them among treatments of AOA,HT and the control.These data suggest that H_2S is induced by chilling stress,and exogenous H_2S alleviates photoinhibition and stimulates the chilling tolerance in cucumber seedlings.