School of Biological and Chemical Sciences, Queen Mary University of London, UK.
Plant Signal Behav. 2011 Sep;6(9):1386-90. doi: 10.4161/psb.6.9.16503.
Using freeze-fracture electron microscopy we have recently shown that non-photochemical quenching (NPQ), a mechanism of photoprotective energy dissipation in higher plant chloroplasts, involves a reorganization of the pigment-protein complexes within the stacked grana thylakoids. Photosystem II light harvesting complexes (LHCII) are reorganized in response to the amplitude of the light driven transmembrane proton gradient (ΔpH) leading to their dissociation from photosystem II reaction centers and their aggregation within the membrane1. This reorganization of the PSII-LHCII macrostructure was found to be enhanced by the formation of zeaxanthin and was associated with changes in the mobility of the pigment-protein complexes therein1. We suspected that the structural changes we observed were linked to the ΔpH-induced changes in thylakoid membrane thickness that were first observed by Murikami and Packer. Here using thin-section electron microscopy we show that the changes in thylakoid membrane thickness do not correlate with ΔpH per se but rather the amplitude of NPQ and is thus affected by the de-epoxidation of the LHCII bound xanthophyll violaxanthin to zeaxanthin. We thus suggest that the change in thylakoid membrane thickness occurring during NPQ reflects the conformational change within LHCII proteins brought about by their protonation and aggregation within the membrane
我们最近通过冷冻断裂电子显微镜技术发现，非光化学猝灭（NPQ）是高等植物叶绿体中一种光保护能量耗散的机制，涉及到堆叠类囊体中色素-蛋白复合物的重组。光系统 II 光捕获复合物（LHCII）会响应驱动跨膜质子梯度（ΔpH）的幅度进行重组，导致它们从光系统 II 反应中心解离，并在膜内聚集 1。这种 PSII-LHCII 宏观结构的重组被发现可以通过玉米黄质的形成而增强，并与其中色素-蛋白复合物的流动性变化有关 1。我们怀疑我们观察到的结构变化与 Murikami 和 Packer 首次观察到的类囊体膜厚度因 ΔpH 诱导的变化有关。在这里，我们使用薄截面电子显微镜技术表明，类囊体膜厚度的变化与 ΔpH 本身没有相关性，而是与 NPQ 的幅度相关，因此受 LHCII 结合的叶黄素叶黄素向玉米黄质的脱环氧化影响。因此，我们认为在 NPQ 过程中发生的类囊体膜厚度变化反映了 LHCII 蛋白内的构象变化，这是由于它们在膜内的质子化和聚集引起的。
