Queen Mary University of London, School of Biological and Chemical Sciences, London, UK.
J Exp Bot. 2020 Jun 22;71(12):3626-3637. doi: 10.1093/jxb/eraa126.
Plants are subject to dramatic fluctuations in the intensity of sunlight throughout the day. When the photosynthetic machinery is exposed to high light, photons are absorbed in excess, potentially leading to oxidative damage of its delicate membrane components. A photoprotective molecular process called non-photochemical quenching (NPQ) is the fastest response carried out in the thylakoid membranes to harmlessly dissipate excess light energy. Despite having been intensely studied, the site and mechanism of this essential regulatory process are still debated. Here, we show that the main NPQ component called energy-dependent quenching (qE) is present in plants with photosynthetic membranes largely enriched in the major trimeric light-harvesting complex (LHC) II, while being deprived of all minor LHCs and most photosystem core proteins. This fast and reversible quenching depends upon thylakoid lumen acidification (ΔpH). Enhancing ΔpH amplifies the extent of the quenching and restores qE in the membranes lacking PSII subunit S protein (PsbS), whereas the carotenoid zeaxanthin modulates the kinetics and amplitude of the quenching. These findings highlight the self-regulatory properties of the photosynthetic light-harvesting membranes in vivo, where the ability to switch reversibly between the harvesting and dissipative states is an intrinsic property of the major LHCII.
植物的光合作用系统在一天中会受到光照强度的剧烈波动的影响。当光合作用机器暴露在高光下时，会有多余的光子被吸收，这可能导致其脆弱的膜成分发生氧化损伤。一种被称为非光化学猝灭（NPQ）的光保护分子过程是在类囊体膜中进行的最快响应，可以无害地耗散多余的光能。尽管已经进行了深入的研究，但这个基本调节过程的位点和机制仍存在争议。在这里，我们表明，主要的 NPQ 成分称为能量依赖型猝灭（qE）存在于光合作用膜中，这些膜主要富含主要的三聚体光捕获复合物（LHC）II，而缺乏所有的小 LHC 和大多数光系统核心蛋白。这种快速和可逆的猝灭取决于类囊体腔的酸化（ΔpH）。增强 ΔpH 会扩大猝灭的程度，并在缺乏 PSII 亚基 S 蛋白（PsbS）的膜中恢复 qE，而类胡萝卜素玉米黄质则调节猝灭的动力学和幅度。这些发现强调了光合作用光捕获膜在体内的自我调节特性，其中在收集和耗散状态之间可逆切换的能力是主要 LHCII 的固有特性。
