Abstract

Transmission electrón microscopy of thin sections of leaf and root tissues from papaya plants infected by papaya lethal yellowing virus (PLYV) revealed the presence of a large number of spheroidal virions either in the cytoplasm or in the vacuole of infected cells. Virions were also seen in xylem vessels but not in the sieve tubes or laticifers. Virus particles in the vacuole were arranged in a helical manner, forming tubular structures. A majority of the hélices were made of 5 particles per pitch. Less frequently, polyhedral structures with 10 particles in the perimeter were also seen. Viroplasmalike inclusions iriter- spersed with virions were found in the cytoplasm of some cells. PLYV particles could be seen in disrupted root tip epidemial cells which may explain their possible soil transmission of this virus. The viral nature of these particles was confirmed by immunogold labeling experiments using the specific anti-PLYV serum in LRWhite médium. Viroplasmas were also labeled but this may be due to the interspersed coat protein or virions. These cytopathic effects are not characteristic of other known isometric viruses.