Antiviral activity of Boerhaavia diffusa root extract and the physical properties of the virus inhibitor

Abstract

The aqueous extract of air-dried roots of Boerhaavia diffusa shows broad-spectrum antiviral activity and no phytoxic effects. Infection by four viruses was completely prevented, at treated and nontreated sites, when the extract was applied on two basal leaves of host plants 24 h prior to virus inoculation. This inhibition was completely reversed by the application of actinomycin D on treated leaves within 6 h of extract treatment and partially reversed within 18 h. The crude extract from resistant leaves contained an inhibitor of virus infection.The inhibitor in the root extract was partially active up to a dilution of 1:500, was completely inactivated at 95 °C for 10 min, and survived at room temperature for 20 days. The expression of inhibitory activity was prevented when the treated plants were exposed to temperatures beyond 35 °C. The inhibitory principle in the extract was nondialyzable and insoluble in organic solvents, viz., petroleum ether, solvent ether, chloroform, and benzene. It was adsorbed by animal charcoal, wood charcoal, and celite, and was precipitated by ammonium sulphate (90%), ethanol (50%), and cold trichloroacetic acid (10%). The inhibitor was not sedimented at 120 000 × g for 120 min. Further characterization is being done for positive identification of the inhibitor.