Auxin inhibition of flower induction of pharbitis is not mediated by ethylene.

Treatment of whole Pharbitis nil seedlings or cotyledons with indole butyric acid (IBA) immediately before an inductive dark period greatly inhibited flowering. Treatment of the shoot tip alone with IBA had little or no effect. 1-Aminocyclopropane 1-carboxylic acid, which increased ethylene production by the seedlings much more than IBA, had no effect on the flowering response. Pretreatment of seedlings with the ethylene biosynthesis inhibitor aminooxyacetic acid or with the inhibitor of ethylene action silver thiosulfate did not reduce the inhibitory effect of IBA on flower induction. We concluded, therefore, that the auxin-induced inhibition of flowering of P. nil was not mediated by ethylene.