A naturally occurring glycoprotein present in Boerhaavia diffusa root extract (BD inhibitor), causes plant cells to produce a highly active antiviral agent (AVA) that defends cells against infection by viruses. AVA was present in inhibitor-treated plants only, but not in nontreated plants, and was produced 2–48 h after treatment with BD inhibitor. AVA was effective not only in plant species in which it was produced but in other plant species as well. Crude AVA was active both in vitro and in vivo. In vitro, it markedly reduced the infectivity of viruses, and in vivo, the virus content in AVA-treated leaves and leaf discs was considerably suppressed. The AVA showed the characteristics of protein.

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.

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An antiviral substance, showing highly significant virus inhibiting property, has been isolated from the aqueous extract of Cuscuta reflexa plants. The biologically active virus inhibitor was purified by fractionation with organic solvents followed by precipitation with a saturated solution of ammonium sulphate, dialysis, ultracentrifugation and filtration through a Sephadex G-200 column. It shows characteristics of proteins with a molecular weight around 14,000-18,000 daltons. The antiviral activity of the purified material was increased several folds. It has prevented the infection of several unrelated isometric as well as anisometric viruses in their hypersensitive and systemic hosts. Systemic resistance induced in lower treated as well as upper nontreated leaves of host plants, whose lower leaves had been treated with inhibitor, was significantly reversed in presence of Actinomycin D.

An antiviral agent, active against spherical and tubular viruses in hypersensitive and systemic hosts, has been isolated from the roots of Boerhaavia diffusa. Partial purification of inhibitor by organic solvents, Sephadex gel, and protein precipitants has been achieved. Preliminary analysis indicates that the inhibitor may be a glycoprotein with a molecular weight of 16 000–20 000 daltons.

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