behavior of the plasma membrane following osmotic contraction of isolated protoplasts: implications in freezing injury

Following osmotic contraction of isolated rye protoplast (Secale cereale L. cv. Puma) that results in nearly a 50% reduction in volume, the plasma membrane was smooth, with no folding or pleating. Instead, deletion of plasma membrane occurred and numerous cytoplasmic vesicles were observed. As a result, the area of the plasma membrane was reduced by approximately 40%. Thin sections revealed that the cytoplasmic vesicles were membrane bound and not merely voids in the cytoplasm. The results using osmotic manipulation confirm earlier observations of isolated protoplasts at the light microscope level. Upon contraction plasma membrane is deleted into cytoplasmic vesicle, which are not readily reincorporated into the plasma membrane upon expansion. Lysis occurs before the original volume and surface area are regained.