Further Studies of an Inhibitor of Virus Replication from Tobacco Mosaic Virus-Infected Protoplasts of a Local Lesion-Responding Tobacco Cultivar

Abstract

The inhibitor(s) of virus replication (IVR) released into the medium from tobacco mosaic virus (TMV)-infected protoplasts of N. tabacum L. ''Samsun NN'', in which the infection in the intact plant is localized, inhibited virus replication also in leaf tissue disks, in addition to the previously reported evaluation on isolated protoplasts. IVR inhibited replication of tobacco mosaic, cucumber mosaic (CMV), and potato X viruses in leaf disks from different hosts [Cucumis sativus and Capsicum frutescens] indicating that IVR is neither host-nor virus-specific. Inhibition rates, determined by infectivity or by enzyme-linked immunosorbent assay, ranged 60-90%. IVR also inhibited TMV replication in intact leaves when applied to cut stems or by spray. IVR was recovered from intact protoplasts in addition to the incubation medium. IVR did not affect TMV directly and no IVR could be detected in the medium from ''Samsun NN'' protoplasts inoculated with CMV. IVR was sensitive to trypsin and chymotrypsin, but not to RNase, and its activity was abolished by incubation at 60.degree. C for 10 min, suggesting that IVR is proteinaceous.