Effects of sodium chloride on the plasma membrane of halotolerant Dunaliella primolecta: an electron spin resonance study

Electron spin resonance spectroscopy was used to monitor the in vivo microviscosity of the plasma membrane and lipid extracts of the salt tolerant alga, Dunaliella primolecta. The fluidity of the plasma membrane decreased as the algae were adapted to and suspended in higher sodium chloride concentrations [2–24% (w/v)]. Both biochemical modification and a physical interaction between Na⁺ and lipids were implicated.When the microviscosity of the plasma membrane and that of lipid extracts were determined as a function of temperature, two or three lipid phase transformations were observed. There were always transformations at 9–14° C and 39–43° C. These were interpreted as the onset and completion of the lipid phase transition of at least a major lipid component of the membrane, possibly the entire membrane. These transformation temperatures were independent of the salt concentration to which the algae were adapted or suspended. This suggests that D. primolecta exists with some of its membrane in the solid-fluid mixed lipid state. With a NaCl concentration of 8% (w/v) or greater in the growth medium, a third transformation occurred around 20–22° C. It was the result of a lipid-lipid interaction and was not related to adaptation.Abbreviations ESR electron spin resonance spectroscopy - 2 T hyperfine splitting - S order parameter - 5-DS or 5-doxyl-stearate 2-(3-carboxylpropyl)-4,4-dimethyl-2-tridecyl-3-oxazolidinyloxyl