Interpretation of morphological data obtained by freeze-fracturing at very low temperatures.

In freeze-fracture replication the greatest variety of methods exists for the fracturing process itself. The present stage of knowledge allows to evaluate fracture faces obtained by freeze-cleaving at temperatures down to 4 K. Under condensation free conditions the possibility for artefact formation will be restricted to the fracturing and replication process. Experiments on model systems and complex biological systems show that many fine structural details seen on freeze-fractured replicas have to be interpreted as the result of a multi-event process involving plastic deformation, elastic recontraction, collapse phenomena and thermal load induced alterations during replica formation. With some structures the degree of deformation may be reduced by chemical fixation procedures.