Studies on Plant Growth Hormones

Abstract

3-Indolylacetonitrile is more active than 3-indolylacetic acid in the Avena straight-growth test, but less active in the Avena curvature test at comparable concentrations. Reasons for this are discussed, and results of previous work on plant extracts using the curvature test as a means of assay are considered. Transport of both the acid and the nitrile is polar, from apex to base of the coleoptile. The nitrile can reach the growing cells as easily, and possibly more easily, than the acid. The significance of these findings for a theory on the mechanism of action of the nitrile is discussed. The nitrile is inactive in the pea curvature test and straight-growth of pea stem sections except at high concentrations. It is also inactive or only slightly active in lateral bud inhibition, root initiation, and petiole abscission at the concentrations tested. It is less active than the acid in root inhibition in cress, but approximately as active in Avena. It is approximately as active as the acid in parthenocarpic fruit development, and initiation of cambial activity. The significance of these results is discussed.