Arachidonic acid is important for efficient use of light by the microalga Lobosphaera incisa under chilling stressстатья

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1. Полный текст BBALIP-17-29R1_3.pdf 2,2 МБ 4 мая 2017 [solovchenko]

[1] Arachidonic acid is important for efficient use of light by the microalga lobosphaera incisa under chilling stress / B. Zorin, D. Pal-Nath, A. Lukyanov et al. // Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. — 2017. 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 oC; chilling temperatures (≤ 15 oC) 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 oC, the major chloroplast lipid monogalactosylglycerol (MGDG) were 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 oC. 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 is 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. [ DOI ]

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