ULTRASTRUCTURAL COMPARISONS OF DEFECTIVE, PARTIALLY DEFECTIVE, AND NONDEFECTIVE ISOLATES OF IMPATIENS NECROTIC SPOT VIRUS

Cytopathological and serological properties of four isolates of impati ens 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 p aired parallel membranes (PPMs), often in concentric rings. PPMs were continuous with rough endoplasmic reticulum (rER) and the nuclear enve lope and were associated with nucleocapsid aggregates (NCAs) and amorp hous inclusions (AIs). Infections of HT-1 contained NCAs, Als, PPMs th at included modified Golgi bodies, and virion-like particles within pr ominent networks of smooth endoplasmic reticulum (sER). Immunogold lab eling with polyclonal antibodies to the nucleocapsid protein (N protei n) of HT-1 identified the N protein in NCAs and PPMs, including Golgi bodies. Budding at PPMs appeared to form virions, but many particles a ppeared incomplete, and reactions between particles and HT-1 antiserum were erratic. HT-2 infections contained numerous double-enveloped vir ions (DEVs) in the cytoplasm, whereas single-enveloped virions (SEVs) were observed within sER and swollen rER cisternae. Polyclonal antiser um to N protein of INSV strongly labeled NCAs and virions. NCAs and ma sses of SEVs were associated with rER, whereas SEVs within sER were le ss common. Some DEVs appeared to form at Golgi bodies that labeled inc onsistently. Although HT-1 and HT-2 produced virions, differences betw een these two isolates and INSV B may reflect incomplete replication c ycles in the two HT-derived cultures.