The ethyl acetate-soluble, acidic fraction extracted from sporophytes of Ecklonia radiata contains material inhibitory to the growth of dwarf maize plants treated with gibberellic acid, but which did not affect the growth of maize plants not treated with gibberellic acid. Saturation concentrations of gibberellic acid did not overcome the inhibition. It is concluded that the inhibitory material was functioning as a specific antagonist to gibberellin-controlled growth in maize and that a non-competitive component was present.
The inhibitory extract was shown to reduce the growth of gametophytes of Ecklonia when applied to cultures at physiological concentrations. This suggests an endogenous growth regulatory function for the active material, perhaps as a gibberellin antagonist. Higher levels were extracted from blade tissue than from stipe plus transition region tissue.