A simple bioassay for detecting "antitranspirant" activity of naturally occurring compounds such as abscisic acid.

Isolated epidermal strips of Commelina communis L. showed progressively smaller stomatal openings when incubated in abscisic acid solutions ranging in concentration from 10(-8) to 10(-4) M. The effects were reproducible and did not appear to be affected by the presence of auxin, gibberellic acid or kinetin. This specificity suggests that this method may prove valuable as a quick, sensitive bioassay for abscisic acid and other related compounds which might be used as antitranspirants on field crops. The fungal toxin fusicoccin, previously reported to cause increased stomatal opening on intact leaves, partially reversed the closure induced by abscisic acid.