Enhanced tobacco mosaic virus production and suppressed synthesis of a virus inhibitor in protoplasts exposed to antibiotics.

Actinomycin D and chloramphenicol, when added up to 24 hr after inoculation, markedly increased tobacco mosaic virus (TMV) replication in protoplasts of Samsun NN, a cultivar in which the infection in the intact plant is localized. No increase was observed when TMV-infected protoplasts of Samsun, a systemic-responding cultivar, were incubated in the presence of these antimetabolites. Concomitant with the increase in virus replication in protoplasts of Samsun NN, production of the inhibitor of virus replication (IVR) (G. Loebenstein and A. Gera, Virology, 114, 132-139, 1981) from these protoplasts was suppressed almost completely. These results strengthen the suggestion that IVR is associated with the localizing mechanism by suppressing virus replication.