THE DETERMINATION OF PHASEIC ACID BY MONOCLONAL ANTIBODY-BASED ENZYME-IMMUNOASSAY

A monoclonal antibody PA3-2-B3, IgG(1) (lambda) is described which specifically recognizes phaseic acid and shows very little cross-reactivity (0.14 %) with abscisic acid or dihydrophaseic acid (0.88 %). Based on this antibody, an enzyme immunoassay was developed which displays a linearity range from 15 pg to 3 ng of phaseic acid. Results obtained with this assay agree with those obtained by gas chromatography-electron capture detection. Using the novel enzyme immunoassay, as well as an established immunoassay for abscisic acid, levels of these two compounds in leaves of Phaseolus vulgaris were determined as a function of plant age, water stress, recovery from stress, and feeding of abscisic acid through the transpiration stream. The production of phaseic acid in a microsomal system from bean leaves was demonstrated. The results show a regulation of the plant's capacity to metabolize abscisic acid to phaseic acid as a function of water stress.