Comparative Activity of Synthetic Auxins and Derivatives

Abstract

The activity of indoleacetic, indolebutyric, naphthaleneacetic, dichlorophenoxyacetic, and naphthoxyacetic acids and certain derivatives has been tested on deseeded Avena coleoptiles. Intact as well as the usual decapitated coleoptiles were employed, and both agar and lanolin blocks (and lanolin in unilateral smears) were used as carriers. 1. When tested in agar on decapitated coleoptiles, potassium salts of indoleacetic, indolebutyric, and naphthaleneacetic are as active as the free acids. Esters of indolebutyric are of about the same activity as the acid; esters of indoleacetic are less active than the corresponding acid; and esters of naphthaleneacetic acid are inactive. Indoleacetamide, naphthaleneacetamide, and dichlorophenoxyacetic acid are but slightly active. Naphthoxyacetic, its ethyl ester, and naphthoxypropionic acids are completely inactive (although reported by others to be active in the tomato test). 2. When applied in agar to intact coleoptiles, indoleacetic, indolebutyric, and naphthaleneacetic acids are completely inactive. 3. When blocks of lanolin rather than agar are applied to decapitated coleoptiles, ten to fifty times the concentration of indoleacetic, indolebutyric, and naphthaleneacetic acids must be used to give threshold curvatures. In agar, the relative activities of the acids are 100:5:19, respectively; in lanolin, 100:11:11. 4. When applied in lanolin to intact coleoptiles, indoleacetic, indolebutyric, and naphthaleneacetic acids have the same activity as when applied to decapitated coleoptiles; that is, threshold concentrations are the same whether the coleoptiles are intact or decapitated. 5. Levulinic acid is completely inactive in the Avena test, whether applied in lanolin or agar, and has no complementary effect when applied together with indoleacetic acid.