Studies of plant virus inhibitors from legume seeds

Abstract

Seed extracts from 18 varieties of legumes were tested for virus inhibitory activity against TMV. Unheated seed extracts fall into two categories. Those extracts which give 73-95% inhibition and includes G. max (soybean), and extracts in which inhibition is between 0-60%, for example P. vulgaris (French bean). Inhibition was decreased by heating some extracts such as G. max, whilst in other extracts, such as P. vulgaris, the percentage inhibition was increases by heating. P. vulgaris and G. max seed extracts were studied in detail. P. vulgaris was also inhibitory to TMV, whilst G. max was inhibitory to TMV and PVX. Dilution experiments confirmed the presence of inhibitors and not inactivators in both extracts. None of the inhibitors was nucleic acid. However, dialysis precipitation with alcohol or ammonium sulphate and disc electro-phoresis experiments suggested that the inhibitors are composed of proteins and glycoproteins stable to a wide range of ph. Sephadex G-100 gel filtration showed that G. max seed extracts inhibitors have molecular weights of about 158,500 and 17,780. On the other hand, P. vulgaris inhibitors have molecular weights of about 177,800 and 12,590. Seven fractions were obtained from DEAE chromatography of each of G. max (soybean) and P. vulgaris (French bean) seed extracts. Soybean contains three virus inhibitor fractions, one basic in nature and two acidic. None of the virus inhibitors agglutinated erythrocytes) however, the acidic inhibitors showed inhibition activity. French bean contains also three virus inhibitors as well as confounds reducing the effects of the inhibitors. These are termed masking compounds. Such masking compounds were agglutinins. The basic inhibitor also showed agglutination of erythrocytes whilst only one of the two acidic virus inhibitors showed trypsin inhibition. Plant lectins were also tested for virus inhibition and agglutination activity, and it was found that the situation is complex and although soybean and French bean seed extracts seemed to have surface effect on the susceptibility of the host, the mode of action of lectins and the virus inhibitors are different. The virus inhibitors seem either to affect the attachment of the virus to the infective centres or perhaps allow attachment but prevent entry of virus into the cells.