Mechanical Properties of the Plasma Membrane of Isolated Plant Protoplasts

Abstract

The vome of isolated protoplasts of rye (Secale cereale L. cv Puma) in a suspending solution at constant concentration is shown to be neglgbly changed by tensions in the plasma membrane which approach that tension necessary to lyse them. This aflows a detailed investigation of the plasma membrane stress-strain relation by micropipette aspiration.Over periods less than a second, the membrane behaves as an elastic two-dimensional fluid with an area modulus ofelasticity of230 milnewtons per meter. Over longer periods, the stress-strain relation approaches a surface energy law-the resting tension is independent of area and has a value of the order 100 micronewtons per meter. Over longer periods the untensioned area, which is defhied as the area that would be occupied by the molecules in the membrane at any given time if the tension were zero, increases with time under large imposed tensions and decreases under sufficiently small tension. It is proposed that these long term responses are the result of exchange of material between the plane of the membrane and a reservoir of membrane material. The irreversibility of large contractions in area is demonstrated directly, and the behavior of protoplasts during osmoticaLy induced cycles of contraction and expansion is explained in terms of the membrane stress-strain relation.When the volume of isolated protoplasts is reduced by transferring them to a medium with greater osmotic pressure, the area of their plasma membranes is also reduced and they regain their spherical shape. Thus, osmotic expansions and contractions of spherical protoplasts both produce changes in the area of the plasma membrane.Steponkus and co-workers (22,23,25) have shown that one may ascribe to a population of protoplasts an absolute surface area increment, greater expansions than which cause the plasma membrane to lyse. This increment is independent of the extent of contraction. One form of freeze-thaw injury suffered by protoplasts from nonacclimated tissue is the result of incompletely reversible contractions of the plasma membrane during freezing of the suspending medium (22,23,25). These studies suggest that, during large deformation, the mechanical properties of the plasma membrane of isolated protoplasts are qualitatively different from l

Voltage-dependent K + channel gating and voltage sensor toxin sensitivity depend on the mechanical state of the lipid membrane

“…By contrast, large membrane vesicles unrestrained by boundaries can have very low tensions (Ͻ 10 Ϫ2 mN/m) (39,40). Likewise, the tension of cell membranes under normal physiological conditions is near zero (41,42). Cell membranes typically have ''excess membrane'' in the form of folds and invaginations.…”

Freezing, Drying, and/or Vitrification of Membrane– Solute–Water Systems

“…For small changes, the two are proportional and the constant of proportionality is called the area elastic modulus. This has been measured for lipid bilayers, and for animal and plant membranes using micropipette aspiration (Mitchison and Swann, 1954;Wolfe and Steponkus, 1983;Evans and Needham, 1987). Because the lamellae have very low volumetric compressibilities, a fractional reduction in area is associated with a nearly equal fractional increase in thickness.…”

Electron Tomographic Analysis of Somatic Cell Plate Formation in Meristematic Cells of Arabidopsis Preserved by High-Pressure Freezing[W]

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