Monoclonal antibodies against fusicoccin with binding characteristics similar to the putative fusicoccin receptor of higher plants

Abstract

Monoclonal antibodies were raised against fusicoccin. The toxin, linked to bovine serum albumin through its t-pentenyl moiety, served as immunogen. Hybridomas secreting anti-fusicoccin antibodies were screened by radioimmunoassay employing a novel radioactive derivative, [(3)H]-nor-fusicoccin-alcohol of high specific activity (1.5 x 10(14)Bq/mole). The two monoclonal antibodies reported here are of high apparent affinity for fusicoccin (0.71 x 10(-9) molar and 1.85 x 10(-9) molar). This is comparable to the apparent affinity of rabbit antiserum raised against the same type of conjugate (9.3 x 10(-9) molar). A method for the single step purification of the monoclonal antibodies from ascites fluid is reported. A solid-phase immunoassay, using alkaline phosphatase as enzyme, exhibits a measuring range from 0.1 to 1.5 picomoles (about 70 picograms to 1 nanogram) of fusicoccin. The displacement of [(3)H]-nor-fusicoccin-alcohol from the antibodies by compounds structurally related to fusicoccin exhibits similar selectivity as a microsomal binding assay with the same tracer as radiolabeled probe.