Arachidonic acid is important for efficient use of light by the microalga Lobosphaera incisa under chilling stress Academic Article uri icon


  • The oleaginous microalga Lobosphaeraincisa(Trebouxiophyceae, Chlorophyta)contains arachidonic acid (ARA, 20:4 n-6) in all membrane glycerolipids and in the storage lipidtriacylglycerol.The optimal growth temperature of the wild-type (WT) strain is 25°C; chilling temperatures (≤15oC) 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) were dominated by C18/C16 speciesin both strains. Yet ARAconstituted 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 minorcomponent of MGDG in P127. Both strains increased the percentage of18:3 n-3 in membrane lipids under chilling temperatures. The temperature downshift led to a dramatic increase in triacylglycerolat the expense of chloroplast lipids. WT and P127 showed a similarly highphotochemicalquantum 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 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 conditionsin the mutant.

publication date

  • January 1, 2017