Abstract
The purpose of this study was to examine the effect of different growth temperatures on the fatty acid compositions of the photosynthetically important galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), of the “blue” pennate diatom, Haslea ostrearia, and the model pennate diatom, Phaeodactylum tricornutum, with the hypothesis that their sn-2 fatty acids would be modulated in the same manner as for dinoflagellates. Positive-ion electrospray ionization/mass spectrometry/mass spectrometry was used to characterize the galactolipids of each diatom. At 20°C, H. ostrearia and P. tricornutum were rich in eicosapentaenoic acid (EPA; C20:5) at the sn-1 position and in C16 fatty acids at the sn-2 position of MGDG and DGDG. At 30°C, however, H. ostrearia and P. tricornutum contained no EPA or other C20 fatty acids, but rather contained higher percentages of C18 fatty acids at sn-1. At 30°C, no galactolipid in either diatom contained more than three unsaturations on any of its fatty acids. While these two species differ in galactolipid composition, they both possess a similar method of acclimating their galactolipids to a higher growth temperature: reducing the numbers of the longest and shortest fatty acid chains, as well as decreasing the total number of unsaturations.
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