Sequential appearance of capsid protein and cylindrical inclusion protein in root-tip cells following infection with passion fruit woodiness virus

Early events in passion fruit woodiness virus (PWV) infection of root-tip cells of tobacco (Nicotiana benthamiana) were examined by immunoelectron microscopy with antisera prepared specifically against the capsid protein (CP) and cylindrical inclusion protein (CIP) of the virus. Capsid protein was first detected on the cytoplasmic virus-specific vesicles coincident with first appearance of virions, but virions were not visible at every location that was stained. Early configurations of cylindrical inclusions (CI) were first observed on the surface of endoplasmic reticulum. At a later stage when aggregates of PWV were present, PWV virions were intimately associated with CIs either within the cytoplasm or attached perpendicularly to the cell wall. Most PWV aggregates were bound to cytoplasmic membranous structures in cells at a late stage of infection. Antiserum against CP partially reacted with CIs at advanced stages of infection. On the other hand, antiserum against CIP reacted only with CIs, but not with PWV virions. Both CP and CIP could also be detected in the plasmodesmata of infected cells.