Plant virus inhibitors extracted from the Caryophyllaceae

Abstract

Thirty species from the family Caryophyllaceae were found to contain inhibitors of local lesion production by TNV. The crude extracts of 20 species totally eliminated lesion production. Dilution experiments revealed the presence of at least two materials in the extracts of some species, an inhibitor which decreased and an augmenter which increases the number of lesions. Heat treatment decreases inhibitory activity in some species and not in other. Two species were studied in detail, Gypsophila paniculata which showed powerful inhibitory activity was partially thermostable and Minuratia capillacea which showed weak thermolabile inhibition. The constituents of Gp extracts acted as virus inhibitors rather than inactivators, survived at room temperature for 60 days, and were stable to a wide range of pH. Dialysis experiments confirmed that the inhibitory activity resided in both high and low molecular weight compounds. Ethanol or ammonium sulphate precipitation, and disc electrophoresis suggested that the inhibitors are composed in part, of protein and glycoprotein. Furthermore, inhibitory activity could not be attributed to RNA, but remained unchanged after incubation with each of three proteolytic enzymes, Sephadex G-100 gel filtration showed that Gp extract inhibitors to have a molecular weights of about 12,600 - 27,500 and 2,000 for the materials which eluted slowly. Ion exchange column chromatography on CM-52 cellulose showed that extracts contained at least three virus inhibitor fractions, one neutral and two basic in nature. The low molecular weight fraction, dialysable part, contained 17 free amino acids most of which had inhibitory activity against TNV, and 3 free sugars all of which stimulated local lesion production. Aqueous extracts prepared from G.paniculata and M.capillacea each inhibit local lesion production by TNV, TMV and PVX viruses. The G.paniculata inhibitors seem to have direct effects on TNV and some was precipitated on centrifugation. Minuratia inhibitors are not precipitated by centrifugation. Inhibition in both extracts influences host plants and acts either by altering the susceptibility of the cells to virus attachment, or perhaps allow penetration and prevent early events of virus replication. The crude extracts from Gp induced local and systemic resistance in untreated parts of the plant. Systemic resistance was induced on French bean leaves when Gp extracts were applied to their roots. The sample taken from resistant leaves contained an inhibitor of virus infection and showed 3 additional protein bands with molecular weights of 105, 94 and 40 x10-3daltons on SDS polyacrylamide gel electrophoresis. Gp = Gypsonhila paniculata TMV = tobacco mosaic virusTNV = tobacco necrosis virus PVX ss potato virus X