DICTYOSOME-ENDOPLASMIC RETICULUM ASSOCIATIONS IN HIGHER-PLANT CELLS - A SERIAL-SECTION ANALYSIS

Abstract

Serial sections through permanganate and glutaraldehyde/osmium-fixed dictyosomes from suspension-cultured sycamore maple cells and maize root cap cells were analyzed. Transition vesicles between ER [endoplasmic reticulum] and the dictyosome and a forming face to the dictyosome were not present. Direct, tubular ER-cisternal connections were doubtful, if at all present. Maturing faces to dictyosomes i.e., a polarity in terms of the pinching-off of secretory vesicles, were not a typical feature. Two types of vesicle were associated with the dictyosome: large and small. Cisternae were present as a flattened, continuous central portion at whose periphery an extensive, anastomosing tubule system exists. Cisternae in the dictyosome stack were not concentrically arranged but were somewhat dispersed. A characteristic feature of maize dictyosomes was a bilateral or unilateral distribution of hypertrophied slime vesicles. The kidney-shaped slime vesicles are arranged opposite to one another at the tubular periphery of a cisterna; the region in between is filled with smaller, occasionally coated vesicles. The endomembrane concept is not applicable to higher plant cells whose main secretory product is polysaccharide rather than protein. Consequences and alternatives in relation to membrane-flow in such cells are discussed.