Dictyosome-endoplasmic reticulum associations in higher plant cells? A serial-section analysis

Serial sections through permanganate and glutaraldehyde/osmium fixed dictyosomes from suspension cultured sycamore cells and maize root cap cells have been analyzed. The results may be summarized as follows. For both sycamore and maize dictyosomes are: 1. transition vesicles between ER and dictyosome, and therefore a "forming face" to the dictyosome, not present. 2. direct, tubular ER-cisternal connections doubtful, if at all present; 3. "Maturing faces" to dictyosomes, i.e. a polarity in terms of the pinching-off of secretory vesicles, not a typical feature; 4. two types of vesicle associated with the dictyosome: large and small (in part "coated"); 5. cisternae present as a flattened, continuous central portion at whose periphery an extensive, anastomosing tubule system exists; 6. cisternae in the dictyosome stack not concentrically arranged, but lie somewhat displaced to one another. A characteristic feature of maize dictyosomes, in addition, is a bi- or unilateral distribution of hypertrophied slime vesicles. The kidney-shaped slime vesicles are arranged opposite to one another at the tubular periphery of a cisternae; the region in between is occupied with smaller, occasionally coated, vesicles. It would appear from these results that the endomembrane concept sensu strictu [58] 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.