THE MONOCLONAL-ANTIBODY JIM19 MODULATES ABSCISIC-ACID ACTION IN BARLEY ALEURONE PROTOPLASTS

A panel of hybridoma products generated against pea (Pisum sativum L.) guard-cell protoplasts has been assayed for anti-abscisic acid (ABA) biological activity in barley (Hordeum vulgare L.) aleurone protoplast s. The effects of the antibodies on ABA-induced accumulation of mRNA t ranscribed from RAB-16, a gene responsive to ABA, were determined. Mos t of the antibodies, and culture medium, had no effect, but five monoc lonal antibodies (MAbs) were found to inhibit ABA-induced RAB-16 gene expression and one MAb enhanced it. The effects of one inhibitory MAb, JIM19, were studied in some detail. These effects were specific to AB A-induced events, as incubation with JIM19 had no effect on the expres sion of a constitutively-expressed gene, GAPDH, encoding glyceraldehyd e-3-phosphate dehydrogenase, and only a slight effect on the productio n of a-amylase induced by gibberellic acid. Increasing concentrations of ABA in the incubation medium partly overcame the inhibitory effect of JIM19. Immunolabelling and biological activity remained together du ring immune-purification of JIM19 from hybridoma culture supernatant. Immunoblotting of JIM19 to membrane preparations from barley aleurone protoplasts revealed that JIM19 recognised a number of proteins.