Ultrastructural comparisons of defective, partially defective, and nondefective isolates of impatiens necrotic spot virus

Cytopathological and serological properties of four isolates of impatiens necrotic spot virus (INSV), Igg, HT-1, HT-2, and B, were compared in infected Impatiens 'Accent Salmon.' Igg was a defective form of the virus that failed to form virions but induced extensive networks of paired parallel membranes (PPMs), often in concentric rings. PPMs were continuous with rough endoplasmic reticulum (rER) and the nuclear envelope and were associated with nucleocapsid aggregates (NCAs) and amorphous inclusions (AIs). Infections of HT-1 contained NCAs, AIs, PPMs that included modified Golgi bodies, and virion-like particles within prominent networks of smooth endoplasmic reticulum (sER). Immunogold labeling with polyclonal antibodies to the nucleocapsid protein (N protein) of HT-1 identified the N protein in NCAs and PPMs, including Golgi bodies. Budding at PPMs appeared to form virions, but many particles appeared incomplete, and reactions between particles and HT-1 antiserum were erratic. HT-2 infections contained numerous double-enveloped virions (DEVs) in the cytoplasm, whereas single-enveloped virions (SEVs) were observed within sER and swollen rER cisternae. Polyclonal antiserum to N protein of INSV strongly labeled NCAs and virions. NCAs and masses of SEVs were associated with rER, whereas SEVs within sER were less common. Some DEVs appeared to form at Golgi bodies that labeled inconsistently. Although HT-1 and HT-2 produced virions, differences between these two isolates and INSV B may reflect incomplete replication cycles in the two HT-derived cultures