Rapid cellular changes were observed in the vascular tissue of
Sicot 189 three days after inoculation using transmission electron
microscopy. Vessel lumens in uninfected xylem tissue appeared
empty and the adjacent contact parenchyma cells had a single large
central vacuole, with the remainder of the cytoplasm adpressed to
the cell wall (Fig.1a). In the contact cells of infected plants electrondense
and granular materials filled the cells and accumulated in
vessel lumens (Fig. 1b). The dense osmiophilic material sometimes
occluded vessel lumens before spreading through the pits between
cells (Fig. 1c). Sometimes the material clung together to form
a globular mass not apparently associated with any tylosis