Mono- and digalactosyldiacylglycerol composition of dinoflagellates. IV. Temperature-induced modulation of fatty acid regiochemistry as observed by electrospray ionization/mass spectrometry

Members of the dinoflagellate genus Pyrocystis possess forms of mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively) that have the C20 fatty acid eicosapentaenoic acid [20:5(n-3)] at the sn-1 position and either octadecapentaenoic acid [18:5(n-3)] or octadecatetraenoic acid [18:4(n-3)] at the sn-2 position. We have examined the effect of growth at 15 degrees C, 20 degrees C, and 25 degrees C on modulation of the fatty acids associated with MGDG and DGDG in two strains of each of three species of Pyrocystis, P. fusiformis, P. lunula, and P. noctiluca and have observed using positive-ion electrospray ionization/mass spectrometry (ESI/MS) and electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS) that modulation of the sn-2 fatty acid of DGDG was the only consistent, statistically significant temperature response across all three species. Only one strain of P. lunula displayed a statistically significant temperature-induced modulation of MGDG. In addition, the effect of growth temperature on two forms of the recently identified lipid, trigalactosyldiacylglycerol (TGDG), was examined; TGDG displayed a statistically significant temperature response in only one strain of P. noctiluca. The results presented herein demonstrate how DGDG is modified preferentially over MGDG and TGDG in response to growth temperature by modulating the sn-2 fatty acid of DGDG between the 18:5(n-3) and 18:4(n-3) forms, while the sn-1 fatty acid, 20:5(n-3), remained constant.