Inhibitor(s) of virus replication (IVR) and localization of viruses in plants.

A substance(s) inhibiting virus replication (IVR) is released into the medium from tobacco mosaic virus-infected protoplasts of a cultivar in which the infection in the intact plant is localized. IVR inhibited virus replication in protoplasts from both resistant (Samsun NN) and susceptible (Samsun) plants, when applied up to 18 h after inoculation. It was not produced in protoplasts from susceptible plants or from noninoculated protoplasts of the resistant cultivar. IVR was partially purified using ZnAc2 precipitation, and yielded two biologically active principles with molecular weights of about 26,000 and 56,000 daltons. Preliminary results indicate that IVR inhibits replication of TMV and several other non-related viruses when applied to inoculated leaf disks.