Changes in excitation relaxation of diatoms in response to fluctuating light, probed by fluorescence spectroscopies
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ORIGINAL ARTICLE
Changes in excitation relaxation of diatoms in response to fluctuating light, probed by fluorescence spectroscopies Miyuki Tanabe1 · Yoshifumi Ueno1 · Makio Yokono2 · Jian‑Ren Shen3 · Ryo Nagao3 · Seiji Akimoto1 Received: 28 November 2019 / Accepted: 10 February 2020 © Springer Nature B.V. 2020
Abstract A marine pennate diatom Phaeodactylum tricornutum (Pt) and a marine centric diatom Chaetoceros gracilis (Cg) possess unique light-harvesting complexes, fucoxanthin chlorophyll a/c-binding proteins (FCPs). FCPs have dual functions: light harvesting in the blue to green regions and quenching of excess energy. So far, excitation dynamics including FCPs have been studied by altering continuous light conditions. In the present study, we examined responses of the diatom cells to fluctuating light (FL) conditions. Excitation dynamics in the cells incubated under the FL conditions were analyzed by time-resolved fluorescence measurements followed by global analysis. As responses common to the Pt and Cg cells, quenching behaviors were observed in photosystem (PS) II with time constants of hundreds of picoseconds. The PSII → PSI energy transfer was modified only in the Pt cells, whereas quenching in FCPs was suggested only in the Cg cells, indicating different strategy for the dissipation of excess energy under the FL conditions. Keywords Light harvesting · Energy transfer · Fluctuating light · Diatom · Photosystem Abbreviations AFDA Absolute fluorescence decay-associated Chl Chlorophyll CL Continuous light FCP Fucoxanthin Chl a/c-binding protein FDA Fluorescence decay-associated FL Fluctuating light Fx Fucoxanthin LED Light-emitting diode LHC Light-harvesting complex LHCSR LHC stress-related PS Photosystem RC Reaction center TRF Time-resolved fluorescence * Ryo Nagao nagaoryo@okayama‑u.ac.jp * Seiji Akimoto [email protected]‑u.ac.jp 1
Graduate School of Science, Kobe University, Kobe 657‑8501, Japan
2
Innovation Center, Nippon Flour Mills Co., Ltd., Atsugi 243‑0041, Japan
3
Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama 700‑8530, Japan
Introduction Light-harvesting and energy-transfer processes in photosynthesis are modified in response to light environments. Among numerous light conditions, high-light-induced regulations of the processes have been extensively studied (Demming-Adams et al. 2014). Under the high-light conditions, excess excitation energy is dissipated into heat at lightharvesting complexes (LHCs) or reaction centers (RCs) of photosystems (PSs). Some cyanobacteria exhibit the orange carotenoid protein, which binds to allophycocyanin, the core protein of cyanobacterial antenna phycobilisome (Kirilovsky and Kerfeld 2012). Green plants possess one or both of two LHC-like proteins, the PSII subunit S (called as PsbS) (Li et al. 2000; Alboresi et al. 2010; Correa-Galvis et al. 2016), and the LHC stress-related (LHCSR) (Peers et al. 2009; Alboresi et al. 2010). These quenching mechanis
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