Changes in the ordering of lipids in the membrane of Dunaliella in response to osmotic-pressure changes. An e.s.r. study

Abstract

Changes in the ordering and motion of lipids in response to changes in the external solute concentration have been studied by using the 5-nitroxide stearate (5NS) and 16-nitroxide stearate (16NS) spin probes in the plasma membrane of the halotolerant unicellular alga Dunaliella salina. Increases in ordering of the 5NS probe and decreases in motion of the 16NS probe were observed in cells equilibrated over 18 h at increasing NaCl concentrations. These changes probably resulted from the influence of the high NaCl concentration on the charged phospholipid head groups of the membrane. A short-term (less than 100 min) decrease in the order parameter, S, of the 5NS probe was observed for cells swollen by exposure to a sudden decrease of NaCl concentration from 5.0 to 2.5 M. After 100 min the value of S for 5NS was close to the value obtained in cells that had been equilibrated in 2.5 M-NaCl for 18 h. Since the cells had regained their original size and shape by 100 min it was assumed that the short-term decrease in S was associated with the swelling. A similar result was obtained when the cells were suddenly changed from 3.0 M- to 1.5 M-sorbitol. Conversely, an increase in S was observed for cells shrunk when the external solute concentration was doubled from 1.5 M- to 3.0 M-NaCl. As the cells regained their original size and shape the value of S decreased to the value observed in cells that had been equilibrated in 3.0 M-NaCl for 18 h. It is suggested that the changes in S are related to the movement of lipid into or out of a reservoir of membrane material as the membrane shrinks or expands. This movement of lipid maintains the tension of the membrane below the value at which it is disrupted. Such changes in lipid ordering could provide a mechanism whereby information about external osmotic-pressure changes is transmitted across the cell wall.

Salt-induced Changes in the Plasma Membrane Proteome of the Halotolerant Alga Dunaliella salina as Revealed by Blue Native Gel Electrophoresis and Nano-LC-MS/MS Analysis

“…Salt-induced changes in organellar membranes, such as the expression of ER fatty acid elongase, were also reported (7). High salinity also affects sodium transport (8), lipid organization (9,10), and activation of PM protein kinases (11). Taken together, the accumulated evidence suggested that short and long range reorganization of the structure and composition of the PM is at the core of molecular mechanisms responsible for the salinity response.…”

“…Early studies in Dunaliella reported global changes in plasma membrane fluidity in response to osmotic shock. Specifically hyperosmotic shocks resulted in rigidification, whereas hypoosmotic shocks led to transient fluidization of the membrane core (9,10,14). Moreover we previously showed that sterols have a crucial role in osmotic sensing in D. salina (61).…”

Spin probe clustering in human erythrocyte ghosts

“…from Acanthamoeba castellani [30], mouse mastocytoma cells [29], rat macrophages [24], human lens [31], renal brush-border membranes of rabbit [13], and outer membranes of Dunaliella salina [9]. The nature of the spectral changes suggested that these effects were not due to perturbations in membrane structure, but were a consequence of radical interactions resulting from spin probe clustering [7,20].…”

Characterization of genes and enzymes in Dunaliella salina involved in glycerol metabolism in response to salt changes

“…salina has mainly focused on the glycerol metabolism pathway and also the involvement of the plasma membrane (Curtain et al . ; Zelazny et al . ; Katz et al .…”