Sucrose-gradient-purified dictyosomes of plant Golgi apparatus appear, after glutaraldehyde stabilization, as stacks of highly fenestrate and tubate cisternae when negatively stained with phosphotungstic acid, shadowed with heavy metal, or OsO4-stained in thin section. The tubular proliferations (diameter 200 to 400 A) extend for several microns from the central region and are united at intervals into an anastomosing network. Associated with the tubules are two kinds of vesicles which are distinguishable on the basis of texture, size, shape, and staining characteristics. One vesicle type is rough-surfaced, nearly spherical, and of uniform dimensions (diameter approximately 600 A). Metal shadowing shows that these vesicles remain spherical after drying. The other vesicle type is smooth-surfaced and varies in both size and shape. Intercisternal elements are revealed, by negative staining, on the surface of internal cisternae after fragmentation of the dictyosome. The progressive differentiation of cisternae from the forming face to the maturing face is observed in thin sections of these isolated preparations. The morphological characteristics observed in negatively stained dictyosomes indicate regions of functional specialization within the dictyosome cisternae and reveal a dictyosome structure more extensive than that envisioned from sections.

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