Auxin Structure & Abscission Activity

Abstract

The effects of various auxins on leaf abscission of Phaseolus vulgaris have been compared by studying the abilities of indoleacetic acid, naphthalene-acetic acid and various phenoxyacetic acids to inhibit or to promote abscission. The compounds were selected to represent a range of auxin activity associated with substitutions of the aromatic ring, of the acidic side chain, and with optical isomerism. Using the bean abscission test, it was found that all of the compounds tested were capable of inhibiting abscission. Some inhibitory activity was obtainable even from compounds with no detectable growth activity. But the relative inhibitory effects were increased with structural changes which increased the growth activity of the auxin. The promotive effects on abscission were restricted to those compounds which do have auxin activity in growth. This was especially evident when the promotive effects were released by including an induction period before the application of the auxins or auxin analogues. All of the auxins tested share in a quantitative way the ability to inhibit abscission and to promote abscission.