[Alleviating effect of exogenous melatonin and calcium on the peroxidation damages of cucumber under high temperature stress].

To explore whether there is an interaction between melatonin (MT) and calcium (Ca2+) in regulating heat tolerance of plants, we analyzed the response of endogenous MT and Ca2+ to heat stress, and examined the effect of MT and Ca2+ on the reactive oxygen (ROS) accumulation, antioxidant system, and transcripts of heat shock factor (HSF) and heat shock proteins (HSPs) of cucumber seedlings under high temperature stress. Seedlings were foliar sprayed with 100 μmol·L-1 MT, 10 mmol·L-1 CaCl2, 3 mmol·L-1 ethylene glycol tetraacetic acid (EGTA, Ca2+ chelating agent) +100 μmol·L-1 MT, 0.05 mmol·L-1 chlorpromazine (calmodulin antagonist, CPZ) +100 μmol·L-1 MT, 100 μmol·L-1 p-chlorophenylalanine (p-CPA, inhibitor of MT) +10 mmol·L-1 CaCl2 or deionized water (H2O), respectively. The results showed that both endogenous MT and Ca2+ in cucumber seedlings were induced by high temperature stress. The seedlings treated with exogenous MT showed significant increases in the mRNA expression of calmodulin (CaM), calcium-dependent protein kinase (CDPK5), calcineurin B-like protein (CBL3) and CBL interacting protein kinase (CIPK2) compared with the control at normal temperature. The mRNA levels of tryptophane decarboxylase (TDC), 5-hydroxytryptamine-N-acetyltransferase (SNAT) and N-acetyl-5-hydroxytryptamine methyltransferase (ASMT), key genes of MT biosynthesis and endogenous MT content were also induced by Ca2+ in cucumber seedlings. Exogenous MT and CaCl2 alleviated the heat-induced oxidative damage through increasing antioxidant ability, reducing the accumulation of reactive oxygen species (ROS), and upregulating the mRNA abundances of HSF7, HSP70.1 and HSP70.11, as evidenced by mild thermal damage symptoms, lower heat injury index and electrolyte leakage under heat stress. The positive effect of MT-induced antioxidant capacity and mRNA expression of HSPs was removed by adding EGTA and CPZ in stressed seedlings. Similarly, the mitigating role of Ca2+ in the peroxidation damage to high temperature stress was reversed by p-CPA. These results suggested that both MT and Ca2+ could induce heat tolerance of cucumber seedlings, which had crosstalk in the process of heat stress signal transduction.为了探明褪黑素(MT)和钙离子(Ca2+)在调控植物耐热性中是否存在互作关系,以黄瓜幼苗为试材,分析了内源MT和Ca2+对高温胁迫的响应;并通过叶面喷施100 μmol·L-1 MT、10 mmol·L-1 CaCl2、3 mmol·L-1乙二醇二乙醚二胺四乙酸(EGTA,Ca2+螯合剂)+100 μmol·L-1 MT、0.05 mmol·L-1氯丙嗪(钙调素拮抗剂,CPZ)+100 μmol·L-1 MT、100 μmol·L-1氯苯丙氨酸(p-CPA,MT合成抑制剂)+10 mmol·L-1 CaCl2和去离子水(H2O),研究高温下(42/32 ℃)外源MT和Ca2+对黄瓜幼苗活性氧积累、抗氧化系统及热激转录因子(HSF)和热激蛋白(HSPs)等的影响。结果表明: 黄瓜幼苗内源MT和Ca2+均受高温胁迫诱导;外源MT可上调常温下钙调素蛋白(CaM)、钙依赖蛋白激酶(CDPK5)、钙调磷酸酶B类蛋白(CBL3)、CBL结合蛋白激酶(CIPK2)mRNA表达;CaCl2处理的MT合成关键基因色氨酸脱羧酶(TDC)、5-羟色胺-N-乙酰转移酶(SNAT)和N-乙酰-5-羟色胺甲基转移酶(ASMT)水平也显著升高,MT含量快速增加。MT和CaCl2可显著增强高温下黄瓜的抗氧化能力,减少活性氧(ROS)积累,同时上调HSF7、HSP70.1和HSP70.11 mRNA表达,从而减轻高温胁迫引起的过氧化伤害,植株热害症状明显减轻,热害指数和电解质渗漏率显著降低。加入EGTA和CPZ后,MT对黄瓜幼苗抗氧化能力和热激蛋白表达的促进效应明显减弱,Ca2+对高温下黄瓜幼苗过氧化伤害的缓解效应也被p-CPA逆转。可见,MT和Ca2+均可诱导黄瓜幼苗的耐热性,二者在热胁迫信号转导过程中存在互作关系。.