Light and electron microscopy of cytoplasmic and unusual nuclear inclusion bodies evoked by a virus from necrotic peas

Abstract

Light microscopic examinations of leaves of Pisum sativum and some other plant species, infected with a virus tentatively called pea necrosis virus, revealed the presence of granular cytoplasmic inclusions and of hitherto unreported nuclear inclusions. Abnormal nuclei contained considerably, and mostly irregularly, enlarged nucleoli, which were usually covered with peculiar radiating needles. Electron microscopy showed flexuous particles, presumably virus particles, at random in the cytoplasm of ultrathin sections. The particles were sometimes aggregated into irregular bundles or were spirally arranged. Electron-dense bands were found to occur separately or in pinwheel structures as reported for other viruses of the potato virus Y group. Cytoplasmic organelles were only slightly affected. Inside the needle-containing nuclei no nucleoli nor nucleolar material could be observed. Large electron-dense, radiating bars were found in the nucleoplasm, deforming the nucleus by pushing out the nuclear membrane. They correspond to the needles observed by light microscopy. Even at high magnification, no ultrastructure could be detected.