Red (hot) algae: modulation of mono- and digalactosyldiacylglycerol-associated fatty acids of Polysiphonia sp. and Porphyridium sp. in response to growth temperature

Abstract

ABSTRACTThere is a dearth of surveys examining the direct effects of temperature on red algal galactolipids, and none which examine regiochemistry modulation with respect to growth temperature. Therefore, forms of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), the two most commonly found galactolipids in chloroplast membranes, were determined in two model red algae, Polysiphonia sp. and Porphyridium sp., via positive-ion electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS. We sought to compare modulation of galactolipid forms in response to growth temperature between these two red algae and selected descendants with red algal plastid ancestry, and have proposed the following hypothesis: Polysiphonia sp. and Porphyridium sp. would modulate desaturations in the sn-2 position in accordance with previously examined descendant organisms. It was observed that both red algae produced C20/C16 (sn-1/sn-2 regiochemistry) and C20/C20 forms of MGDG and DGDG as their most abundant galactolipids under two growth temperatures, 20°C and 30°C. Furthermore, temperature-induced modulation of the major forms of MGDG and DGDG was more complex than what has been observed previously in selected representatives of red algal plastid ancestry. Porphyridium sp. modulated levels of desaturation in the sn-1 position of C20/C16 forms of MGDG and DGDG and in the sn-1 and sn-2 positions of C20/C20 forms of MGDG and DGDG. Polysiphonia sp. displayed trends suggesting it modulates levels of desaturation in the sn-1 and sn-2 positions of C20/C20 forms of MGDG and DGDG, thus indicating a different approach to regulating plastid membrane fluidity from that which has been observed in algae with secondary, red algae-derived plastids.