Green plants protect against photodamage by dissipating excess energy in a process called non-photochemical quenching (NPQ). In vivo, NPQ is activated by a drop in the luminal pH of the thylakoid membrane that triggers conformational changes of the antenna complexes, which activate quenching channels. The drop in pH also triggers de-epoxidation of violaxanthin, one of the carotenoids bound within the antenna complexes, into zeaxanthin, and so the amplitude of NPQ in vivo has been shown to increase in the presence of zeaxanthin. In vitro studies on light-harvesting complex II (LHCII), the major antenna complex in plants, compared different solubilization environments, which give rise to different levels of quenching and so partially mimic NPQ in vivo. However, in these studies both completely zeaxanthin-independent and zeaxanthin-dependent quenching have been reported, potentially due to the multiplicity of solubilization environments. Here, we characterize the zeaxanthin dependence of the photophysics in LHCII in a near-physiological membrane environment, which produces slightly enhanced quenching relative to detergent solubilization, the typical in vitro environment. The photophysical pathways of dark-adapted and in vitro de-epoxidized LHCIIs are compared, representative of the low-light and high-light conditions in vivo, respectively. The amplitude of quenching as well as the dissipative photophysics are unaffected by zeaxanthin at the level of individual LHCIIs, suggesting that zeaxanthin-dependent quenching is independent of the channels induced by the membrane. Furthermore, our results demonstrate that additional factors beyond zeaxanthin incorporation in LHCII are required for full development of NPQ.

绿色植物通过在称为非光化学猝灭（NPQ）的过程中耗散多余的能量来防止光害。在体内，NPQ被类囊体膜的管腔pH下降激活，从而触发天线复合体的构象变化，从而激活淬灭通道。pH的下降也触发了紫黄质素（绑定在天线复合物中的一种类胡萝卜素）脱环氧化为玉米黄质，因此，在玉米黄质存在下，体内NPQ的振幅会增加。对植物中主要的天线复合物光采复合物II（LHCII）的体外研究比较了不同的增溶环境，这导致了不同程度的淬灭并因此部分模拟了NPQ体内。然而，在这些研究中，已经报道了完全不依赖玉米黄素的和依赖玉米黄素的淬灭，这可能是由于增溶环境的多样性。在这里，我们表征了在近生理膜环境中LHCII中光物理对玉米黄素的依赖性，相对于典型的体外环境中的去污剂增溶作用，其产生的淬灭性略有增强。比较了暗适应和体外脱环氧化的LHCII的光物理途径，代表了体内的弱光和强光条件， 分别。玉米黄质在各个LHCIIs的水平上均不影响猝灭的幅度以及耗散的光物理性质，这表明玉米黄素依赖性猝灭与膜诱导的通道无关。此外，我们的结果表明，将玉米黄质掺入LHCII之外的其他因素是NPQ全面发展所必需的。