Light microscopic studies of zinnia leaf tissues infected with dahlia mosaic virus (DMV) revealed spherical, refractile inclusions within the cells. In cytochemical studies, the inclusions stained intensely for proteins (fast green) and weakly for RNA (azure B), possibly in association with the peripheral ribosomes; tests for DNA (Feulgen) were negative. From electron microscopic observations, these inclusions consisted of a finely granular matrix with electron transparent areas of varying size. The inclusions were not membrane bound; however, ribosomes were always located at the periphery. The diameter of the inclusions varied from 0.2 to 10 μ. Spherical particles, 400-450 Å in diameter, which commonly appeared ring-like in profile occurred within the dense granular matrix and electron transparent areas of the inclusion. Occasionally, free particles were also observed within the cytoplasm, plasmodesmata, sieve tubes, and tracheary elements. On the basis of pathological, cytological, and morphological criteria, the particles are considered as dahlia mosaic virions. Numerous Golgi bodies (dictyosomes) and thick-walled microvesicles (100-200 mμ) were observed in close proximity to the inclusions. The topological association of the DMV-induced inclusions with the Golgi complex suggests that the latter is involved in their formation. © 1969.
