Carrot Red Leaf and Carrot Mottle Viruses: Observations on the Composition of the Particles in Single and Mixed Infections

Publisher Website
Google Scholar
Abstract
SUMMARY Particles of carrot red leaf virus (CRLV; luteovirus group) purified from chervil (Anthriscus cerefolium) contain a single ssRNA species of mol. wt. about 1.8 × 106 and a major protein of mol. wt. about 25 000. CRLV acts as a helper for aphid transmission of carrot mottle virus (CMotV; ungrouped) from mixedly infected plants. Virus preparations purified from such plants possess the infectivity of both viruses but contain particles indistinguishable from those of CRLV; some of the particles are therefore thought to consist of CMotV RNA packaged in CRLV coat protein. When RNA from such preparations was electrophoresed in agarose/polyacrylamide gels, CMotV infectivity was associated with an RNA band that migrated ahead of the CRLV RNA band and had an estimated mol. wt. of about 1.5 × 10 6, similar to that previously found for the infective ssRNA extracted directly from Nicotiana clevelandii leaves infected with CMotV alone. Preparations of dsRNA from CMotV-infected N. clevelandii leaves contained two species: one of mol. wt. about 3.2 × 10 6, presumably the replicative form of the infective ssRNA, and the other, mol. wt. about 0.9 x 10 6, of unknown origin and function. The infective agent in buffer extracts of CMotV- infected N. clevelandii was resistant to RNase (although the enzyme acted as a reversible inhibitor of infection at high concentrations) and is therefore not unprotected RNA. It may be protected within the approximately 52 nm enveloped structures previously reported. Carrot red leaf virus (CRLV; Watson et al., 1964) was purified by Waterhouse & Murant (1981) and shown to be a luteovirus. A second virus, carrot mottle (CMotV), which is ungrouped, commonly occurs together with CRLV in infected carrot (Daucus carota) plants and depends on it for transmission by the aphid Cavariella aegopodii (Watson et al., 1964). However, CMotV is transmissible by manual inoculation whereas CRLV is not. Data from serological neutralization and other types of experiment (Waterhouse & Murant, 1983) indicated that, in mixed infections of the two viruses in chervil (Anthriscus cerefolium), some particles are produced that consist of CMotV RNA in a coat composed partially or entirely of CRLV protein; presumably these are the particles that enable CMotV to be transmitted by C. aegopodii. In thin sections of Nicotiana clevelandii leaves infected with CMotV alone, Murant et al. (1969) found approximately 52 nm enveloped structures which they suggested might be the particles of the virus; partially purified preparations containing them, along with much cell membrane material, were infective. However, the possibility was not excluded that the structures were cytopathic vesicles involved in early stages of virus replication. Halk et al. (1979) showed that infective CMotV ssRNA, which is readily extracted from infected N. clevelandii leaves, migrated in agarose/polyacryl- amide gels as a molecule ofmol, wt. about 1.5 × 106 to 1.6 × 106. In this paper we describe some additional observations on the composition of particles purified from chervil infected with CRLV alone, or with CRLV + CMotV, and on the nature of the infective particles in N. clevelandii infected with CMotV alone.

This publication has 0 references indexed in Scilit: