Baculovirus Replication: Electron Microscopy of the Sequence of Infection of Trichoplusia ni Nuclear Polyhedrosis Virus in Spodoptera frugiperda Cells

SUMMARY The basic sequence of morphological development of Trichoplusia ni nuclear polyhedrosis virus (NPV) in Spodoptera frugiperda cells at a temperature optimal for virus replication has been determined. The development of this virus is similar to that reported for other baculoviruses with nuclear virogenic stroma preceding nucleocapsid, virus particle and polyhedron production; envelopment of nucleocapsids occurs de novo within the nucleus or by acquisition at the nuclear or plasma membranes. Cells in which virus DNA synthesis was arrested by blocking with cytosine arabinoside failed to show virus development beyond the appearance of a stroma without nucleocapsids. Cells in which virus-specified polypeptides were rendered non-functional by azetidine incorporation at prescribed periods delayed morphological change. This development is discussed in relation to the basic biochemical changes which occur in infected cells.