OCCURENCE OF VIRUS PARTICLES IN PHLOEM TISSUE OF BYDV-INFECTED BARLEY

Electron microscopy of leaves and roots of barley (Hordeum vulgare L.) infected with barley yellow dwarf virus (BYDV) has shown densely staining spherical particles, about 24 mμ in diameter, in certain phloem cells. These particles are interpreted as the barley yellow dwarf virions. Size, shape, appearance, and distribution of these particles differentiate them from objects found in uninfected plant cells. Cross sec-sections of a vascular bundle show very few cells in the phloem bundle containing virus particle, thus indicating little lateral spread of the virus from cell to cell. However, longitudinal sections reveal that the virions are spread throughout cells connected in a vertical series. Cells containing virus particles show complete disruption of cell organelles and a fine fibrous network which fills the background cytoplasm. Virus concentration in a cell may very from a few widely scattered particles to dense masses that fill all space not occupied by degenerate cell organelles. The cytological aspects of BYDV infection are discussed in relation to other persistently borne, aphid-transmitted viruses. © 1969.