Intracellular localization and morphology of rhabdovirus-like particles in dodder (Cuscuta sp.)

Rhabdovirus-like particles were discovered in a piece of vine with haustoria of the flowering parasitic plant dodder (Cuscuta sp.). The particles occurred in the perinuclear space or distensions of it and were often arranged in paracrystalline arrays. Most longitudinally sectioned particles were rod shaped and had a round tip, a planar base, and very frequently also a membranous basal bulb. The mean length from the base to the apex was 212.1 nm (SD 13.5 nm, n = 29). The mean outer diameter in cross sections was 63.4 nm (SD 3.7 nm, n = 50). Cross-section profiles comprised an outer coat, with the dimensions of a cellular membrane, and a core of mean diameter 24.9 nm (SD 2.4 nm, n = 20), which appeared as an electron-opaque annulus or stellate ring with an electron-lucent center. Bacilliform particles of approximately double length, with two rounded ends, some of which appeared as two rod-shaped ones joined base to base by a common coat, were observed infrequently. In their morphology, their dimensions, and their intracellular localization these particles resembled rhabdoviruses of unknown origin or significance. Intranuclear rodlets associated with heterochromatin may represent a stage in the assembly of the rhabdovirus-like particles, or a second type of virus-like particles. This is the first report that a species of Cuscuta can be a carrier of what most likely is a rhabdovirus of as yet unknown taxonomic affinities.