Selective modification of cytoplasmic membrane fluidity by catalytic hydrogenation provides evidence on its primary role in chilling susceptibility of the blue-green alga, Anacystis nidulans

Abstract

Cytoplasmic and thylakoid membranes were isolated at different stages of catalytic hydrogenation of fatty acyl double bonds in living cells of Anacystis nidulans. The reaction was limited to the lipids of cell-surface membranes during the initial period of hydrogenation, thus, we were able to produce alga cells, modified exclusively in the cytoplasmic membrane. In these unique cells, neither compositional nor physical changes were detected in the lipid phase of thylakoids. Due to the rigidification of the alkyl chains of its lipids, however, the cytoplasmic membrane became leaky and phase separated at considerably higher chilling temperatures.Since an irreversible inactivation of photosynthetic electron transport was found simultaneously, it provided direct evidence for the hypothesis that the thermotropic properties of the lipids within cytoplasmic membranes, and not those of the thylakoids, control chilling susceptibility of the blue-green alga, A.nidulans.