AN IMPROVED BIO‐ASSAY FOR ABSCISIC ACID AND OTHER ANTITRANSPIRANTS

Abstract

SUMMARY A greatly improved method is described for the bio‐assay of abscisic acid (ABA) and other compounds that possess ‘antitranspirant’ activity. As in the previous method, the stomatal responses are observed on pieces of isolated epidermis of Commelina communis immersed in small volumes of solution containing the compounds to be assayed. In new media, it is now possible to obtain linear responses to ABA concentrations over the range 10 ‐4 ‐10 ‐8 M in PIPES buffer at pH 6.8, and over the range 10 ‐7 ‐10 ‐10 M in citrate buffer at pH 5.5. In citrate buffer, it is possible to detect as little as 26 pg of ABA. In both media, the assay is unaffected by the presence of six other growth regulators (auxin, gibberellic acid, kinetin, coumarin, xanthinin and scopoletin) but the stomata closed partially in response to 10 ‐3 M chlorogenic acid.