Effets de deux types de refroidissements sur l'ultrastructure des ébauches foliaires du Picea abies. I. Etude après fixation chimique

Abstract

Deep freezing of Norway Spruce twigs alters the cell ultrastructure of leaf buds. Upon progressive cooling down, contraction of the protoplasm, the formation of clear areas in the cytoplasm and in organelles, and a condensation of the heterochromatin occur. These changes are reversible; they result from the partial dehydration of the buds caused by the freezing of the twigs and from the conditions of fixation. A continuous and quick cooling of the twigs brings about a fatal intracellular crystallisation and then breaks the cytomembranes.