Radioimmunoassay for brassinosteroids and its use for comparative analysis of brassinosteroids in stems and seeds ofPhaseolus vulgaris

Antiserum against the brassinosteroid (BR), castasterone, was produced by immunizing a rabbit with castasterone-carboxymethoxylamine oxime conjugated with bovine serum albumin (BSA). In a radioimmunoassay (RIA), the antiserum recognized a range of naturally occurring BRs with varying specificities. Detection limits of castasterone and brassinolide were approximately 0.3 pmol. This RIA system was successfully used for analyzing endogenous BRs in seeds and stems ofPhaseolus vulgaris L., and showed that stems are quite different from seeds in terms of the species and quantity of the endogenous BRs.