Ribosome-inactivating proteins and agglutinins from callus and suspension cultures of Ricinus communis L. and Abrus precatorius L.

Abstract

Ribosome-inactivating proteins (RIPs) or toxins, as well as agglutinins, were isolated from callus and cell suspension cultures that were established from seed explants of Ricinus communis L. and Abrus precatorius L. The toxins viz. ricin from R. communis and abrin from A. precatorius as well as agglutinins viz., Ricinus communis agglutinin (RCA) and Abrus precatorius agglutinin (APA) were synthesized in these cultures and were secreted into the medium. The lectins (RIPs and agglutinins) were synthesized through several passages of cultured cells at levels which make them attractive as an alternate source of lectins. Biosynthesis of these carbohydrate-binding proteins was regulated by specific exogenous hormones and was positively correlated with the growth of the cultures indicating that toxins and agglutins may have a role to play during cell division. The toxins and agglutinins were secreted into the medium providing a clue that they probably serve as defence molecules. Secretion of lectins into the medium facilitated easy isolation of the lectins. The synthesized lectins were purified from cultures and were partially characterized. They were biologically active, and were found to be comparable with lectins from seeds, in terms of their electrophoretic mobilities.