Electron microscopic evidence for the presence of barley stripe mosaic virus in cells of barley embryos

Abstract

Barley stripe mosaic virus (BSMV) was demonstrated in thin sections of fully developed barley embryos ( Hordeum vulgare L.) with the electron microscope. Embryos dissected from seed produced on either greenhouse-grown Atlas barley artificially infected with the type strain of BSMV or field-grown Compana, Unitan, or Hypana barley infected naturally with a field strain of BSMV were cut into half portions. One portion was assayed for BSMV antigen by immunodiffusion in agar gel while the other was held in distilled water at 4° for 12–24 hours prior to its fixation by either the aldehyde-osmium or the potassium permanganate method. Embryos similarly prepared from noninfected Atlas barley grown in the greenhouse served as controls. When sections of parenchyma cells from half-embryos which corresponded to half-embryos shown to contain BSMV antigen were viewed, aggregates of tubular-shaped structures identified as BSMV particles or virions were detected in the ground cytoplasm. No membrane surrounded the aggregates. BSMV was not seen in nuclei. The type strain of BSMV in Atlas barley embryos was indistinguishable from a field strain of BSMV in all other barley embryos studied. No virus particles were visible in cells of embryos in which BSMV antigen could not be demonstrated. Eight of 16 half Hypana barley embryos, corresponding to halves previously shown to contain BSMV antigen, caused barley stripe mosaic symptoms when inoculated to Hypana barley seedlings. The aldehyde-osmium and the potassium permanganate methods of fixation to demonstrate BSMV in embryo cells are evaluated for their possible usefulness in the study of embryo infection and seed transmission in barley.