To determine the mitigating effects of exogenous melatonin on salt-alkali stress in cucumber, we mea-sured photosynthetic characteristics and osmoregulatory substance content of cucumber leaves under salt-alkali stress, using 'Xinchun 4' cucumber as the test material and a salt-alkali complex (NaCl:Na2SO4:Na2CO3:NaHCO3 = 1:9:1:9) to simulate stress. The results showed that compared with the normal seedlings, the exogenous application of 10 μmol·L-1 melatonin significantly increased the contents of chlorophyll, soluble sugar, and soluble protein, as well as net photosynthetic rate, stomatal conductance, transpiration rate, photosystem Ⅱ maximum photochemical efficiency, actual photochemical efficiency, apparent photosynthetic electron transfer rate, and photochemical burst coefficient of cucumber seedlings under 40 mmol·L-1 salt-alkali stress, but decreased intercellular CO2 concentration, non-photochemical burst coefficient, and sucrose, fructose, starch, and proline contents by 11.1%, 13.8%, 12.7%, 27.5%, 1.3% and 32.8%, respectively. Moreover, the activities of key enzymes for carbon assimilation (including ribulose-1,5-bisphosphate carboxylase/oxygenase and fructose-1,6-bisphosphate esterase) were significantly increased, whereas the mRNA expression levels of Rubisco subunits (CsrbcS and CsrbcL), CsFBA, CsRCA, CsFBPase and CsTK were downregulated. In conclusion, exogenous melatonin could increase the contents of chlorophyll and osmoregulatory substance, photosynthetic chemical efficiency, and key carbon assimilation enzyme activities of cucumber seedlings under salt-alkali stress, thereby enhance photosynthetic capacity and reduce the stress-induced plant damage. The results would provide theoretical basis for anti-saline plant cultivation.
为明确外源褪黑素(MT)对黄瓜盐碱胁迫的缓解效应,以‘新春四号’黄瓜为试材,采用复合盐碱(NaCl∶Na2SO4∶Na2CO3∶NaHCO3=1∶9∶1∶9)模拟胁迫,测定外源根施MT和盐碱胁迫下黄瓜叶片光合特性和渗透调节物质含量。结果表明: 与正常生长黄瓜幼苗相比,在40 mmol·L-1盐碱胁迫下,外源施加10 μmol·L-1 MT能够显著增加黄瓜幼苗叶片的叶绿素、可溶性糖和可溶性蛋白质含量,提高净光合速率、气孔导度、蒸腾速率、光系统Ⅱ最大光化学效率、实际光化学效率、表观光合电子传递速率和光化学淬灭系数,而胞间CO2浓度、非光化学淬灭系数、蔗糖、果糖、淀粉和脯氨酸含量减小了11.1%、13.8%、12.7%、27.5%、1.3%和32.8%,同时,碳同化关键酶核酮糖-1,5-二磷酸羧化/加氧酶、果糖-1,6-二磷酸酯酶活性显著升高,且Rubisco亚基(CsrbcS和CsrbcL)、CsFBA、CsRCA、CsFBPase、CsTK的mRNA水平均下调表达。综上,外源MT能够提高盐碱胁迫下黄瓜幼苗的叶绿素、渗透调节物质含量、光合化学效率和碳同化关键酶活性,增强幼苗光合能力,减轻复合盐碱胁迫对植株的伤害。研究结果可为抗盐碱栽培提供理论依据。.
Keywords: cucumber; melatonin; osmoregulatory substance; photosynthetic property; salt-alkali stress.