Abstract
The rice stripe virus, a circulative and propagative virus transmitted by Laodelphax striatellus, has been considered to be a spherical particle of about 30nm in diameter. However, branched filamentous particles of, about 400nm in total length and about 8nm in width were found in rice leaves infected with the virus by the direct negative staining method. These particles are quite different in morphology from any other virus particles so far reported, but have never been found in healthy rice leaves. These particles were purified from the virus-infected rice leaves by 10% sucrose cushion centrifugation, chloroform treatment followed by Triton X-100 treatment, sucrose density gradient centrifugation, and finally by D2O sucrose equilibrium centrifugation. The purified preparation containing a large number of the branched filamentous particles but no spherical particles showed to retain infectivity in inoculation tests by microinjections to L. striatellus, and also showed to be a nucleoprotein by UV absorption spectrum. From these results it is concluded that the rice stripe virus is a branched filamentous particle. When observed at high magnifications under the electron microscope, the particle is a slender filament, 3nm in width, of circular structure which usually takes the form of a super-coiled helix. The pitch of the secondary helix is 6nm. No uniformity is found in the number of branches, and sometimes some parts of the particle show loop-like pattern due to partial loosening of the super-coiled helix.
