Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling.
Exogenous Melatonin Mitigates Photoinhibition by Accelerating Non-photochemical Quenching in Tomato Seedlings Exposed to Moderate Light during Chilling.
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DOI：
10.3389/fpls.2017.00244
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发表时间：
2017
影响因子：
5.6
通讯作者：
Zhang S
中科院分区：
文献类型：
--
作者：
Ding F;Wang M;Liu B;Zhang S
褪黑素在植物对多种逆境的耐受中起着重要作用。最近的研究表明，褪黑素缓解了植物在冷胁迫下的光抑制；然而，其机制尚不完全清楚。非光化学猝灭(NPQ)是植物用来防止光系统II过度还原的一种保护机制，是一种关键的热耗散过程。本文报道了外源褪黑素对NPQ的影响以及在低温过程中中等光照下番茄幼苗光抑制的缓解。在低温条件下，光系统II的最大量子效率(Fv/Fm)和有效光化学效率(F‘v/Fm)均显著降低，表现出严重的光抑制效应，而外源褪黑激素能有效地缓解光抑制效应。进一步的实验表明，褪黑激素加速了对中等光照的NPQ的诱导，并在低温期间较长时间的光照下保持了较高的NPQ水平。与NPQ增加一致的是，在褪黑激素处理的幼苗中，在低温期间暴露于光下的叶黄素色素的去环氧化状态增加。酶活性测定表明，在叶黄素循环中催化脱环氧化反应的紫黄质脱环氧酶(VDE)在光的作用下被激活，褪黑素的应用进一步增强了VDE的活性。进一步分析表明，在中等光照和低温条件下，褪黑激素诱导番茄幼苗VDE基因的表达。抗坏血酸是VDE的重要辅助因子，在褪黑激素处理的幼苗中，其含量增加。用VDE抑制剂二硫苏糖醇处理番茄幼苗，可阻断褪黑激素对叶黄素脱环氧化和NPQ诱导的影响。综上所述，这些结果表明，外源褪黑素通过刺激VDE活性和增强叶黄素色素的去环氧化状态来加速NPQ，从而减轻光抑制。
Melatonin plays an important role in tolerance to multiple stresses in plants. Recent studies have shown that melatonin relieves photoinhibition in plants under cold stress; however, the mechanisms are not fully understood. Non-photochemical quenching (NPQ) is a key process thermally dissipating excess light energy that plants employ as a protective mechanism to prevent the over reduction of photosystem II. Here, we report the effects of exogenous melatonin on NPQ and mitigation of photoinhibition in tomato seedlings exposed to moderate light during chilling. In response to moderate light during chilling, the maximum quantum yield (Fv/Fm) and the effective photochemical efficiency (F′v/F′m) of PSII were both substantially reduced, showing severe photoinhibition in tomato seedlings, whereas exogenous application of melatonin effectively alleviated the photoinhibition. Further experiment showed that melatonin accelerated the induction of NPQ in response to moderate light and maintained higher level of NPQ upon longer exposure to light during chilling. Consistent with the increased NPQ was the elevated de-epoxidation state of xanthophyll pigments in melatonin-pretreated seedlings exposed to light during chilling. Enzyme activity assay showed that violaxanthin de-epoxidase (VDE), which catalyzes the de-epoxidation reaction in the xanthophyll cycle, was activated by light and the activity was further enhanced by application of melatonin. Further analysis revealed that melatonin induced the expression of VDE gene in tomato seedlings under moderate light and chilling conditions. Ascorbic acid is an essential cofactor of VDE and the level of it was found to be increased in melatonin-pretreated seedlings. Feeding tomato seedlings with dithiothreitol, an inhibitor of VDE, blocked the effects of melatonin on the de-epoxidation state of xanthophyll pigments and the induction of NPQ. Collectively, these results suggest that exogenous melatonin mitigates photoinhibition by accelerating NPQ through the stimulation of VDE activity and the enhancement of de-epoxidation state of xanthophyll pigments.