Profiles of photosynthetic glycerolipids in three strains of Skeletonema determined by UPLC-Q-TOF-MS

An exhaustive qualitative and quantitative profiling of the photosynthetic glycerolipids in three strains of the marine diatom Skeletonema sp. was carried out by ultra performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry. In the diatom thylakoid membrane, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) account for about 45–70% and 5–15% of the total membrane lipids, respectively. The anionic sulfoquinovosyldiacylglycerol (SQDG) as well as the likewise anionic phosphatidylglycerol (PG) contribute between 10–40% and 4–10% each. The predominant species of MGDG were those with C_16:3/C_16:3, C_20:5/_16:1, and C_20:5/C_16:3. Three main molecular species of DGDG contained C_20:5/C_16:1, C_20:5/C_16:2, and C_16:1/C_16:1. The major molecular species of SQDG were those containing combinations of C_14:0/C_14:0, C_14:0/C_16:0, C_14:0/C_16:1, and C_14:0/C_16:3. All the PG classes contained the C_18:1/C_18:1 as the main molecular species. Based on the fatty acid species in sn-2 position, it is indicated that MGDG and DGDG are biosynthesized through prokaryotic pathway exclusively within the chloroplast, whereas PG and SQDG have a typical mixed biosynthetic pathway (both prokaryotic pathway and eukaryotic pathways). The chemical characteristics of photosynthetic glycerolipids related with ecological physiology are discussed.