低温胁迫下外源褪黑素对番茄幼苗光抑制的缓解效应

为了探究外源褪黑素对低温逆境条件下番茄光合系统破坏的缓解机制,设置常温+水(NW)、常温+褪黑素(NM)、低温+水(CW)、低温+褪黑素(CM)4个处理,对番茄幼苗光合与叶绿素荧光参数、叶绿体抗坏血酸-谷胱甘肽(AsA-GSH)循环效率进行分析。结果表明: 与NW相比,CW的光合速率下降了50.3%～72.6%,叶绿体中的丙二醛含量升高了17.5%～132.7%,超氧阴离子产生速率、H₂O₂含量分别升高了86.5%～235.9%、96.6%～208.4%;而低温下施用褪黑素显著缓解了这一趋势,CM处理光合速率比CW提升了22.7%～24.7%,丙二醛含量、超氧阴离子产生速率、H₂O₂含量分别降低了16.6%～29.0%、14.9%～22.7%、10.7%～27.1%。与CW相比,CM处理光系统Ⅱ光化学能转化系数和调节性能量耗损系数分别升高了15.8%和7.2%,非调节性能量耗损系数下降了24.7%,AsA-GSH循环中关键代谢酶活性均有不同程度的增强。综上,低温下施用外源褪黑素可以平衡光系统Ⅱ的能量分布,增强叶绿体中AsA-GSH循环的活性氧清除效率,进而缓解低温引起的光抑制。

Mitigation of exogenous melatonin on photoinhibition of tomato seedlings under chilling stress

To understand the mitigation effects of melatonin on the chilling-induced photoinhibition in tomato, four groups of seedlings were labelled: NW (normal temperature + water), NM (normal temperature + melatonin), CW (chilling + water) and CM (chilling+ melatonin). We measured chlorophyll fluorescence, key photosynthetic parameters and the cycle efficiency for chloroplast ascorbic acid-glutathione (AsA-GSH). The results showed that, compared with the NW control, photosynthesis rate in CW was decreased by 50.3%-72.6%, chloroplast malondialdehyde content was decreased by 17.5%-132.7%, superoxide anion production was increased by 86.5%-235.9%, and H₂O₂ was increased by 96.6%-208.4%. These trends were significantly alleviated by exogenous melatonin, with photosynthetic rates in CM being increased by 22.7%-24.7% compared with in CW, malondialdehyde content being decreased by 16.6%-29.0%, the rate of superoxide anion production being decreased by 14.9%-22.7%, H₂O₂ content being decreased by 10.7%-27.1%. Compared with CW, the quantum yield of photochemical energy in PS Ⅱ was increased by 15.8% in CM, the quantum yield of regulated non-photochemical energy loss was increased by 7.2%, the quantum yield of non-regulated non-photochemical energy loss was decreased by 24.7%, and the activities of key metabolic enzymes in the AsA-GSH cycle were increased to different degrees. We concluded that exogenous melatonin application could alleviate photoinhibition in tomato seedlings under chilling by balancing the partitioning of absorption energy in PS Ⅱ and by enhancing the ROS scavenging efficiency of the AsA-GSH cycle in the chloroplast.