Xanthophyll cycles are broadly important in photoprotection, and the reversible de‐epoxidation of xanthophylls typically occurs in excess light conditions. However, as presented in this review, compiling evidence in a wide range of photosynthetic eukaryotes shows that xanthophyll de‐epoxidation also occurs under diverse abiotic stress conditions in darkness. Light‐driven photochemistry usually leads to the pH changes that activate de‐epoxidases (e.g. violaxanthin de‐epoxidase), but in darkness alternative electron transport pathways and luminal domains enriched in monogalactosyl diacyl glycerol (which enhance de‐epoxidase activity) likely enable de‐epoxidation. Another ‘dark side’ to sustaining xanthophyll de‐epoxidation is inactivation and/or degradation of epoxidases (e.g. zeaxanthin epoxidase). There are obvious benefits of such activity regarding stress tolerance, and indeed this phenomenon has only been reported in stressful conditions. However, more research is required to unravel the mechanisms and understand the physiological roles of dark‐induced formation of zeaxanthin. Notably, the de‐epoxidation of violaxanthin to antheraxanthin and zeaxanthin in darkness is still a frequently ignored process, perhaps because it questions a previous paradigm. With that in mind, this review seeks to shed some light on the dark side of xanthophyll de‐epoxidation, and point out areas for future work.

中文翻译：

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在叶黄素循环的黑暗面发光

叶黄素循环在光保护中非常重要，叶黄素的可逆脱环氧化作用通常发生在过量的光照条件下。但是，如本综述所述，广泛的光合作用真核生物的证据汇编表明，叶黄素脱环氧化作用也发生在黑暗中的各种非生物胁迫条件下。光驱动的光化学通常会导致pH变化，从而激活脱环氧化物酶（例如紫黄质脱环氧化物酶），但在黑暗中，替代的电子传输途径和富含单半乳糖基二酰基甘油（增强脱环氧化物酶活性）的腔结构域可能会导致脱环环氧化。维持叶黄素脱环氧化作用的另一个“阴暗面”是环氧化酶（例如玉米黄质环氧化酶）的失活和/或降解。这种活动对于耐压性有明显的好处，实际上这种现象仅在压力条件下才有报道。然而，需要更多的研究来揭示其机理并了解暗诱导玉米黄质形成的生理作用。值得注意的是，在黑暗中紫黄嘌呤脱环氧化为花药黄素和玉米黄质仍然是一个经常被忽略的过程，也许是因为它质疑了先前的范式。考虑到这一点，本综述旨在揭示叶黄素脱环氧化的阴暗面，并指出未来的工作领域。紫黄质在黑暗中脱环氧化为花药黄素和玉米黄质仍然是一个经常被忽略的过程，也许是因为它对以前的范式提出了质疑。考虑到这一点，本综述旨在揭示叶黄素脱环氧化的阴暗面，并指出未来的工作领域。紫黄质在黑暗中脱环氧化为花药黄素和玉米黄质仍然是一个经常被忽略的过程，也许是因为它对以前的范式提出了质疑。考虑到这一点，本综述旨在揭示叶黄素脱环氧化的阴暗面，并指出未来的工作领域。