Department of Chemistry, University of California, Berkeley, CA 94720.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2017 Aug 15;114(33):E7009-E7017. doi: 10.1073/pnas.1704502114. Epub 2017 Jun 26.
Photosynthetic organisms use various photoprotective mechanisms to dissipate excess photoexcitation as heat in a process called nonphotochemical quenching (NPQ). Regulation of NPQ allows for a rapid response to changes in light intensity and in vascular plants, is primarily triggered by a pH gradient across the thylakoid membrane (∆pH). The response is mediated by the PsbS protein and various xanthophylls. Time-correlated single-photon counting (TCSPC) measurements were performed on to quantify the dependence of the response of NPQ to changes in light intensity on the presence and accumulation of zeaxanthin and lutein. Measurements were performed on WT and mutant plants deficient in one or both of the xanthophylls as well as a transgenic line that accumulates lutein via an engineered lutein epoxide cycle. Changes in the response of NPQ to light acclimation in WT and mutant plants were observed between two successive light acclimation cycles, suggesting that the character of the rapid and reversible response of NPQ in fully dark-acclimated plants is substantially different from in conditions plants are likely to experience caused by changes in light intensity during daylight. Mathematical models of the response of zeaxanthin- and lutein-dependent reversible NPQ were constructed that accurately describe the observed differences between the light acclimation periods. Finally, the WT response of NPQ was reconstructed from isolated components present in mutant plants with a single common scaling factor, which enabled deconvolution of the relative contributions of zeaxanthin- and lutein-dependent NPQ.
光合作用生物利用各种光保护机制将过量的光激发以热的形式耗散，这个过程称为非光化学猝灭（NPQ）。NPQ 的调节允许植物对光强变化做出快速响应，而在维管束植物中，主要是由类囊体膜上的 pH 梯度（∆pH）触发的。这种反应是由 PsbS 蛋白和各种叶黄素介导的。通过时间相关单光子计数（TCSPC）测量来量化 NPQ 对光强变化的响应与玉米黄质和叶黄素的存在和积累的依赖关系。在 WT 和缺乏一种或两种叶黄素的突变体植物以及通过工程化叶黄素环氧化物循环积累叶黄素的转基因系上进行了测量。在 WT 和突变体植物中，观察到 NPQ 对光驯化的响应在两个连续的光驯化周期之间发生变化，这表明在完全黑暗驯化植物中，NPQ 的快速和可逆响应的特征与植物在白天由于光强变化而可能经历的条件有很大的不同。构建了玉米黄质和叶黄素依赖性可逆 NPQ 响应的数学模型，这些模型准确地描述了光驯化期间观察到的差异。最后，通过使用单个共同标度因子从突变体植物中存在的分离组件重建 WT 对 NPQ 的响应，这使得能够解卷积玉米黄质和叶黄素依赖性 NPQ 的相对贡献。
