Freeze-fracture studies on barley plastid membranes I. Wild-type etioplast

Abstract

Etioplasts from wild-type barley seedlings have been isolated and their membranes examined by freeze-fracturing. All the membranes seen in thin sections of fixed etioplasts have been characterised in terms of the number of freeze-fracture particles per square micron, average particle size and size distribution. This was done for both fracture faces of the primary lamellae, the perforated thylakoids resulting from photodispersal of the prolamellar body, and for both membranes of the etioplast envelope. These membranes, which were identified by their morphology and relationship to one another, as known from thin section studies, could be readily distinguished from one another on the basis of their freeze-fracture ultrastructure. The structure of the prolamellar body has also been examined by freeze-fracturing and was consistent with the model proposed from thin section studies. Freeze-fracturing of the tubules formed by low temperature photodispersal of the prolamellar body revealed a particulate fine structure. The data obtained for the freeze-fracture ultrastructure of wild-type etioplast membranes will form the basis for comparison with that of the membranes from barley plastid mutants. © 1978 Carlsberg Laboratory.