Resistance to tobacco necrosis virus induced by salicylate in detached tobacco leaves.

Sodium salicylate reduced both the size and viral antigen content of non-self-limiting necrotic lesions produced by tobacco necrosis virus (TNV) in detached tobacco leaves during the partly localized reaction to virus. The antiviral effect of salicylate occurred at concentrations close to the limits of toxicity, and depended on the timing of administration. Both viral antigen accumulation and lesion size were strongly inhibited by a continuous supply of salicylate before or just after virus infection. Salicylate treatment did not prevent TNV accumulation when given after the establishment of infection or when arrested 24 h after TNV inoculation. Both procedures, however, did limit lesion enlargement. These results constitute a limit for the use of salicylate as a chemotherapeutic agent but do not exclude its use in limiting the pathogenetic effects of the virus. The salicylate treatments induced the formation of four pathogenesis-related proteins (PRs). The PRs formation was stimulated during the first 8 h of treatment and persisted for some time after the salicylate supply was discontinued. No correlation was found between the presence of PRs and the reduction of TNV accumulation: low salicylate concentrations (0.25 mM) inducing the formation of the PRs did not induce resistance against the multiplication and/or cell-to-cell spread of TNV.