[Objective] The objective of this study is to investigate the physiological and biochemical regulation mechanism and regulation pathway of endogenous NO in cucumber seedlings under salt stress.[Method]The effects of nitric oxide synthase inhibitor (L-NAME, Nω-nitro-L-arginine methyl ester hydrochloride), nitrate reductase inhibitor (tungstate) and nitric oxide scavenger (cPTIO, 4-carboxypheny-4,4,5,5-tetramethy limidazoline-1-oxyl-3-oxidepotass-ium salt) on cucumber seedlings under salt stress were studied. The contents of NO, active oxygen metabolism, photosynthetic parameters and chlorophyll fluorescence parameters were used in discussing the results.[Result]Salt stress increased endogenous NO content in the leaves of cucumber seedlings. The application of 200μmol·L-1 L-NAME, 100μmol·L-1 tungstate and 200μmol·L-1cPTIO inhibited the activities of antioxidant enzymes (SOD, POD and POD) in cucumber seedlings under salt stress. Malondialdehyde (MDA) content, superoxide anion free radical (O2·-) production rate and plasma membrane permeability were increased, and the contents of free proline (Pro) and soluble protein were decreased. Peroxidation increased the damage of cucumber seedlings under salt stress. At the same time, the gas exchange parameters Pn, Gs, Tr, Ci, and the chlorophyll fluorescence parameters Fv/Fm,ΦPSⅡ, qP also decreased. However, the NPQ significantly increased, leading to leaf photosynthetic mechanism damage, and the leaf photosynthetic rate decreased.[Conclusion]Under the salt stress, the change of endogenous NO could directly regulate the antioxidant capacity of cucumber seedlings, alleviate the damage of lipid peroxidation and damage to photosynthetic organs, and the active oxygen metabolism and photosynthetic characteristics of cucumber seedlings are mainly controlled by nitric oxide synthase pathway.%[目的]探讨盐胁迫下黄瓜幼苗内源一氧化氮(NO)的生理生化调节机理及其调控途径,为揭示黄瓜的抗盐机理和生产应用提供参考.[方法]以黄瓜幼苗为研究对象,采用一氧化氮合成酶抑制剂(L-NAME,L-硝基精氨酸甲酯)、硝酸还原酶抑制剂(tungstate,钨酸钠)和一氧化氮清除剂(cPTIO,4-羧基苯-4,4,5,5-四甲基咪唑-1-氧-3-氧化物)处理盐胁迫下的黄瓜幼苗,研究处理对黄瓜幼苗叶片内源NO含量、活性氧代谢、光合参数和叶绿素荧光参数的影响.[结果]盐胁迫可诱导黄瓜幼苗叶片内源NO含量增加,采用200μmol·L-1 L-NAME、100μmol·L-1 tungstate和200μmol·L-1 cPTIO处理均抑制了盐胁迫下的黄瓜幼苗叶片中抗氧化酶(超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT))的活性,降低了游离脯氨酸(Pro)、可溶性蛋白质的含量,增加了丙二醛(MDA)含量、超氧阴离子自由基(O2·-)产生速率和质膜透性,使细胞膜脂过氧化加剧,加重了盐胁迫对黄瓜幼苗的损伤.同时,气体交换参数Pn、Gs、Tr、Ci显著降低,叶绿素荧光参数Fv/Fm、ΦPSⅡ、qP降低,NPQ显著升高,导致叶片光合机构受损,叶片光合速率下降.[结论]在盐胁迫条件下,内源NO的变化可能直接调节了黄瓜幼苗的抗氧化能力,有效地缓解了脂膜过氧化伤害和对叶片光合机构的损伤,且黄瓜幼苗的活性氧代谢和光合特性主要通过一氧化氮合酶途径调控.
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