Effect of the disodium salt of cyclopentene β,β′-triketone on the development of infections induced by TMV in the leaves of hypersensitive and susceptible tobacco plants

We show here that the disodium salt of 2-acetyl-5-chloro-4- hydroxycarbonylmethylthiocyclopent-4-ene-1,3-dione (salt 2) inhibits tobacco mosaic virus (TMV)-induced infections in detached leaves of TMV-resistant (Xanthi-nc) and -susceptible (Samsun) varieties of Nicotiana tabacum L. Inoculation of Xanthi-nc leaves with TMV mixed with salt 2 (2 mg/ml) resulted in a significant decrease (78%) in the number of local lesions as compared to leaves inoculated with TMV alone. By applying the salt immediately before or after infection, the inhibitory effect on the number of lesions decreased. The infectivity and content of viral antigen in Samsun leaves inoculated with a mixture of TMV and salt 2 were considerably less early in infection compared to leaves inoculated with TMV only. As the infection progressed, the inhibitory action of salt 2 decreased. Applying the salt 24 h before infection enhanced the number of both local and heat-induced lesions in Xanthi-nc and Samsun leaves, respectively, that is increased the number of “infectious centers” produced on the leaf surface, which probably promoted virus penetration into the host cells. At the same time, pretreatment decreased the infectivity in Xanthi-nc leaf lesions and infectivity and viral antigen accumulation in Samsun leaves. Therefore, the antiviral effects of salt 2 are not because of diminished penetration of the virus into cells, but seem to be caused by salt 2-mediated inhibition of virus replication.