Inhibitor of virus replication released from tobacco mosaic virus-infected protoplasts of a local lesion-responding tobacco cultivar.

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 local lesion-responding resistant, Samsun NN and systemic-responding susceptible, Samsun plants, when applied up to 18 hr after inoculation. It was not produced in protoplasts from susceptible plants nor 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 57,000, as determined by gel filtration.