Adaptation of light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis to different light qualiti
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ORIGINAL ARTICLE
Adaptation of light‑harvesting and energy‑transfer processes of a diatom Chaetoceros gracilis to different light qualities Seiji Akimoto1 · Yoshifumi Ueno1 · Makio Yokono2 · Jian‑Ren Shen3 · Ryo Nagao3 Received: 18 November 2019 / Accepted: 13 January 2020 © Springer Nature B.V. 2020
Abstract Diatoms are a major group of microalgae in marine and freshwater environments. To utilize the light energy in blue to green region, diatoms possess unique antenna pigment–protein complexes, fucoxanthin chlorophyll a/c-binding proteins (FCPs). Depending on light qualities and quantities, diatoms form FCPs with different energies: normal-type and red-shifted FCPs. In the present study, we examined changes in light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis cells grown using white- and single-colored light-emitting diodes (LEDs), by means of time-resolved fluorescence spectroscopy. The blue LED, which is harvested by FCPs, modified energy transfer involving CP47, and suppressed energy transfer to PSI. Under the red-LED conditions, which is absorbed by both FCPs and PSs, energy transfer to PSI was enhanced, and the red-shifted FCP appeared. The red-shifted FCP was also recognized under the green- and yellow-LEDs, suggesting that lack of the shorter-wavelength light induces the red-shifted FCP. Functions of the red-shifted FCPs are discussed. Keywords Light harvesting · Energy transfer · Light adaptation · Diatom · Photosystem Abbreviations AFDA Absolute fluorescence decay-associated Car Carotenoid Chl Chlorophyll FCP Fucoxanthin Chl a/c-binding protein FDA Fluorescence decay-associated LED Light-emitting diode LHC Light-harvesting complex PS Photosystem TRF Time-resolved fluorescence
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11120-020-00713-2) contains supplementary material, which is available to authorized users. * Seiji Akimoto [email protected]‑u.ac.jp * Ryo Nagao nagaoryo@okayama‑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 Oxygenic photosynthesis by cyanobacteria, algae, and plants is indispensable for sustaining almost all aerobic life activities on earth (Dismukes et al. 2001; Blankenship 2014). The photosynthetic reactions start from light-harvesting events responsible for pigment molecules of chlorophylls (Chls) and carotenoids (Cars). The pigments are associated with two photosynthetic protein complexes, photosystem I and photosystem II (PSI and PSII, respectively), both of which perform charge separation reactions due to a conversion of light energy into chemical energy (Brettel and Leibl 2001; Diner and Rappaport 2002; Busch and Hippler 2011; Lubitz et al. 2019). In addition, the pigment molecules are also bounded to light-
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