Effects of CO 2 and temperature on photosynthetic performance in the diatom Chaetoceros gracilis
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ORIGINAL ARTICLE
Effects of CO2 and temperature on photosynthetic performance in the diatom Chaetoceros gracilis Ryo Nagao1 · Yoshifumi Ueno2 · Seiji Akimoto2 · Jian‑Ren Shen1 Received: 2 October 2019 / Accepted: 18 February 2020 © Springer Nature B.V. 2020
Abstract CO2 concentration and temperature for growth of photosynthetic organisms are two important factors to ensure better photosynthetic performance. In this study, we investigated the effects of C O2 concentration and temperature on the photosynthetic performance in a marine centric diatom Chaetoceros gracilis. Cells were grown under four different conditions, namely, at 25 °C with air bubbling, at 25 °C with a supplementation of 3% C O2, at 30 °C with air bubbling, and at 30 °C with the C O2 supplementation. It was found that the growth rate of cells at 30 °C with the C O2 supplementation is faster than those at other three conditions. The pigment compositions of cells grown under the different conditions are altered, and fluorescence spectra measured at 77 K also showed different peak positions. A novel fucoxanthin chlorophyll a/c-binding protein complex is observed in the cells grown at 30 °C with the CO2 supplementation but not in the other three types of cells. Since oxygenevolving activities of the four types of cells are almost unchanged, it is suggested that the C O2 supplementation and growth temperature are involved in the regulation of photosynthetic light-harvesting apparatus in C. gracilis at different degrees. Based on these observations, we discuss the favorable growth conditions for C. gracilis. Keywords CO2 · Diatom · FCP · Growth temperature · Photosynthesis Abbreviations Chl Chlorophyll FCP Fucoxanthin chlorophyll a/c-binding protein Mes 2-(N-Morpholino)ethanesulfonic acid PS Photosystem
Introduction Diatoms are one of the most successful phytoplankton in aquatic environments which contribute around 40% of the total aquatic primary productivity, or 20% of the total world primary productivity (Field et al. 1998). One of the major factors that may contribute to the success of diatoms is its * Ryo Nagao nagaoryo@okayama‑u.ac.jp * Jian‑Ren Shen [email protected]‑u.ac.jp 1
Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama 700‑8530, Japan
Graduate School of Science, Kobe University, Kobe 657‑8501, Japan
2
possession of a highly efficient C O2-concentrating mechanism (CCM) that allows diatoms to maintain good photosynthetic performance under conditions of low CO2 concentrations in the marine environments (Giordano et al. 2005; Matsuda et al. 2017). There have been several studies about the effects of CO2 on photosynthetic activities in diatoms (Gao and Campbell 2014), and it is generally considered that the elevated CO2 concentrations for cell growth affect cellular metabolisms but not photosynthetic activity, although such CO2 responses differ among different diatom species (Gao and Campbell 2014). We have studied the properties o
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