Temperature shift-induced responses in lipids in the blue-green alga, Anabaena variabilis: the central role of diacylmonogalactosylglycerol in thermo-adaptation.

Changes in fatty acids and lipid molecular species after shift of growth temperature were studied in the blue-green alga, Anabaena variabilis. In the first 10 h after a temperature shift from 38 to 22 degrees C, lipid synthesis was markedly suppressed. During this period most of the palmitic acid of the diacylmonogalactosylglycerol was desaturated to palmitoleic acid. Thereafter lipid synthesis resumed, and, in the following hours, the relative contents of palmitic and palmitoleic acids were almost restored to original levels. On the other hand, the oleic and linoleic acids were almost restored to original levels. On the other hand, the oleic and inoleic acids were desaturated to alpha-linolenic acid in all the lipid classes. The desaturation reaction of the C18 acids were slower than those of the C16 acids. In the first 5 h after a growth-temperature shift from 22 to 38 degrees C, lipid synthesis was considerably stimulated. During this period, the relative content of palmitic acid increased and that of palmitoleic acid decreased in the diacylmonogalactosylglycerol, and in the following 20 h, they were restored. The oleic and linoleic acids increased with a concomitant decrease in alpha-linolenic acid in all the lipid classes. The decreases in unsaturation in the C16 and C18 acids were due to the stimulated synthesis of more saturated fatty acids. Among the major molecular species of the lipids a particular change was seen in 1-oleoyl-2-palmitoylmonogalactosyl-sn-glycerol. This species rapidly decreased after the downward temperature shift and rapidly increased after the upward temperature shift. From the viewpoint of thermo-adaptive regulation of membrane fluidity, the central role played by the diacylmonogalactosylglycerol in temperature acclimation is discussed.