Park Soomin, Fischer Alexandra L, Li Zhirong, Bassi Roberto, Niyogi Krishna K, Fleming Graham R
Department of Chemistry, University of California , Berkeley, California 94720, United States.
Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Phys Chem Lett. 2017 Nov 16;8(22):5548-5554. doi: 10.1021/acs.jpclett.7b02486. Epub 2017 Nov 2.
Nonphotochemical quenching mechanisms regulate light harvesting in oxygenic photosynthesis. Measurement techniques for nonphotochemical quenching have typically focused on downstream effects of quenching, such as measuring reduced chlorophyll fluorescence. Here, to directly measure a species involved in quenching, we report snapshot transient absorption (TA) spectroscopy, which rapidly tracks carotenoid radical cation signals as samples acclimate to excess light. The formation of zeaxanthin radical cations, which is possible evidence of zeaxanthin-chlorophyll charge-transfer (CT) quenching, was investigated in spinach thylakoids. Together with fluorescence lifetime snapshot data and time-resolved high-performance liquid chromatography (HPLC) measurements, snapshot TA reveals that Zea formation is closely related to energy-dependent quenching (qE) in nonphotochemical quenching. Quantitative and dynamic information on CT quenching discussed in this work give insight into the design principles of photoprotection in natural photosynthesis.
非光化学猝灭机制调节着氧光合作用中的光能捕获。非光化学猝灭的测量技术通常聚焦于猝灭的下游效应，比如测量叶绿素荧光的降低。在此，为了直接测量参与猝灭的一个物种，我们报告了快照瞬态吸收（TA）光谱法，该方法在样品适应过量光照时能快速追踪类胡萝卜素自由基阳离子信号。我们在菠菜类囊体中研究了玉米黄质自由基阳离子的形成，这可能是玉米黄质 - 叶绿素电荷转移（CT）猝灭的证据。结合荧光寿命快照数据和时间分辨高效液相色谱（HPLC）测量，快照TA揭示了玉米黄质的形成与非光化学猝灭中的能量依赖猝灭（qE）密切相关。这项工作中讨论的关于CT猝灭的定量和动态信息为自然光合作用中光保护的设计原则提供了见解。
