Journal of Cell Science, Vol 10, 555-561, Copyright © 1972 by Company of Biologists

Submitted on September 2, 1971

Localization of Freeze-Fracture Planes of Yeast Membranes

¹ Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, England

In freeze-etch replicas the position of the plane of fracture along membranes is controversial; in an attempt to clarify the situation we have examined drops of yeast suspension frozen at -160 °C, fractured and then freeze-substituted with a solution of osmium tetroxide in acetone. The drops were embedded in Araldite and sections were cut perpendicular to the plane of fracture to show where the cleavage had occurred.

At the tonoplast the membrane split and the plane of fracture ran between the 2 darkly staining lines. At the plasmalemma the cleavage plane was not clearly localized. The inner half of the membrane remained with the protoplast and darkly staining material could be seen on the wall. However, in some places the dark line at the surface of the protoplast could be resolved into 2 lines. The cleavage plane appeared to change at the invaginations of the plasmalemma, where on fracture the whole membrane sometimes remained attached to the wall.