Membrane differentiation in the Golgi complex of Micrasterias denticulata Bréb. visualized by freeze-etching.

INTRODUCTION In recent years the polarity of dictyosomes has been well established, both iu functional and in morphological terms (Mollenhauer & Morre, 1966; Favard, 1969). Although many of the observed differentiations across stacks of dictyosome cisternae probably result from changes in the Golgi membranes and their associated enzymes, it has only recently been possible to obtain electron-microscope evidence for morphological changes in such membranes (Grove, Bracker & Morre, 1968). However, as these authors point out in their paper, 'the observed differences in membrane morphology represent differences in sites of stain deposition and do not necessarily reflect the morphological forms of the living membranes'. In the present study we have attempted to correlate differences in the staining properties of Golgi membranes of the freshwater alga Micrasterias denticulata (Breb.) (Kiermayer, 1970) with structural features of these membranes as revealed by the freeze-etching electron-microscope preparation technique (Moor & Muhlethaler, 1963), which allows the observation of membrane elements in the frozen state.