Plasma Membrane Lipid Alterations Following Cold Acclimation: Possible Relevance to Freeze Tolerance

Abstract

The plasma membrane plays a central role in cellular behavior during a freeze/thaw cycle and lysis or alterations in its semipermeable characteristics is a primary cause of freezing injury¹. In protoplasts isolated from nonacclimated (NA) rye leaves, injury over the range of 0° to –5°C is a consequence of freeze-induced osmotic contraction resulting in endocytotic vesiculation of the plasma membrane - with sufficiently large area contractions being irreversible. As a result, lysis of the protoplasts occurs during osmotic expansion following thawing of the suspending medium. Alternatively, cooling to temperatures below -5°C results in destabilization of the plasma membrane so that the protoplasts are osmotically unresponsive during thawing of the suspending medium. This form of injury is associated with several changes in the ultrastructure of the plasma membrane, including the formation of lateral phase separations, aparticulate lamellae, and hexagonal_II configurations². Cold acclimation dramatically alters the behavior of the plasma membrane during freeze-induced osmotic contraction and dehydration. In protoplasts from acclimated (ACC) rye leaves, osmotic contraction results in the formation of exocytotic extrusions of the plasma membrane; and at severe levels of dehydration, lateral phase separations, aparticulate lamellae, or H_II configurations are not observed.