Arachidonic acid is important for efficient use of light by the microalga Lobosphaera incisa under chilling stress |
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| Institution: | 1. Microalgal Biotechnology Laboratory, The French Associates Institute for Agriculture and Biotechnology for Drylands, The J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, Midreshet Ben-Gurion 8499000, Israel;2. Department of Bioengineering, Faculty of Biology, Moscow State University, GSP-1, Moscow 119234, Russia;3. Ilse Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Beersheba, Israel;1. Institute of Physiological Chemistry and Pathobiochemistry, University of Münster, D-48149 Münster, Germany;2. National Heart and Lung Institute, Imperial College London, London SW7 2AZ, UK;3. University of Turku, Department of Biochemistry, FI-20014 Turun Yliopisto, Finland;4. Institute of Experimental Musculoskeletal Medicine (IEMM), University of Münster, DE-48149 Münster, Germany;1. Tokyo Institute of Technology, School of Life Science and Technology, Yokohama City, Kanagawa 226-8501, Japan;2. CREST, Japan Science and Technology Agency, Japan;3. Tokyo Institute of Technology, Graduate School of Bioscience and Biotechnology, Yokohama City, Kanagawa 226-8501, Japan;4. Kazusa DNA Research Institute, 2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan;5. Tokyo Institute of Technology, Earth-Life Science Institute, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan;1. Key Laboratory of Child Development and Learning Science (Ministry of education), Research Centre for Learning Science, Southeast University, Nanjing 210096, China;2. Department of Psychiatry, Affiliated Nanjing Brain Hospital of Nanjing Medical University, Nanjing 210029, China;3. Medical School, Nanjing University, 22 Hankou Road, Nanjing 210093, China |
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| Abstract: | The oleaginous microalga Lobosphaera incisa (Trebouxiophyceae, Chlorophyta) contains arachidonic acid (ARA, 20:4 n ? 6) in all membrane glycerolipids and in the storage lipid triacylglycerol. The optimal growth temperature of the wild-type (WT) strain is 25 °C; chilling temperatures (≤ 15 °C) slow its growth. This effect is more pronounced in the delta-5-desaturase ARA-deficient mutant P127, in which ARA is replaced with dihomo-γ-linolenic acid (DGLA, 20:3 n ? 6). In nutrient-replete cells grown at 25 °C, the major chloroplast lipid monogalactosylglycerol (MGDG) was dominated by C18/C16 species in both strains. Yet ARA constituted over 10% of the total fatty acids in the WT MGDG as a component of C20/C18 and C20/C20 species, whereas DGLA was only a minor component of MGDG in P127. Both strains increased the percentage of 18:3 n ? 3 in membrane lipids under chilling temperatures. The temperature downshift led to a dramatic increase in triacylglycerol at the expense of chloroplast lipids. WT and P127 showed a similarly high photochemical quantum yield of photosystem II, whereas non-photochemical quenching (NPQ) and violaxanthin de-epoxidation were drastically higher in P127, especially at 15 °C. Fluorescence anisotropy measurements indicated that ARA-containing MGDG might contribute to sustaining chloroplast membrane fluidity upon dropping to the chilling temperature. We hypothesize that conformational changes in chloroplast membranes and increased rigidity of the ARA-deficient MGDG of P127 at chilling temperatures are not compensated by trienoic fatty acids. This might ‘lock’ violaxanthin de-epoxidase in the activated state causing high constitutive NPQ and alleviate the risk of photodamage under chilling conditions in the mutant. |
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