An homogeneous radioimmunoassay for abscisic acid using a scintillation proximity assay technique

An homogeneous radioimmunoassay (RIA) for the plant growth regulator abscisic acid (ABA) has been developed by modifying an established heterogeneous assay. The introduction of a scintillation proximity reagent has enabled the production of a one‐step RIA in which radioactivity associated with antibody‐bound ABA can be counted in the presence of the unbound radiolabelled ABA and without the addition of a liquid scintillation cocktail. The assay has been validated by comparing the results with those obtained by combined gas chromatography/mass spectrometry and the precision of each method determined. The homogeneous RIA has a working range of 0.165–13.2 ng ABA and has been used to determine ABA concentration in extracts of leaves of tomato, Lycopersicon esculentum Mill. cv. Ailsa Craig (wild type) and three wilty mutants, notabilis, flacca and sitiens.