Abstract
One of the well-characterized phenomena associated with the acclimation of organisms to changes in ambient temperature is the regulation of the molecular motion or "fluidity" of membrane lipids via changes in the extent of unsaturation of the fatty acids of membrane lipids. The enzymes responsible for this process when the temperature is decreased are the desaturases, the activities of which are enhanced at low temperature. To examine whether the change in the fluidity of membrane lipids is the first event that signals a change in temperature, we studied the effect of the Pd-catalyzed hydrogenation of membrane lipids on the expression of the desA gene, which is responsible for the desaturation of fatty acids of membrane lipids in the cyanobacterium Synechocystis PCC6803. The Pd-catalyzed hydrogenation of plasma membrane lipids stimulated the expression of the desA gene. We also found that, for unexplained reasons, the hydrogenation was much more specific to a minor phospholipid, phosphatidylglycerol, than to members of other lipid classes. These results suggest that the organism perceives a decrease in the fluidity of plasma membrane lipids when it is exposed to a decrease in temperature.