Comparative Activity of Synthetic Auxins and Derivatives

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Abstract
The activity of indoleacetic-(IA), indolebutyric-(IB), naphthaleneacetic-(NA), and naphthoxyacetic (NO) acids and certain derivatives have 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. When tested in agar on decapitated coleoptiles, K salts of IA, IB and NA are as active as the free acids. Esters of IB are of about the same activity as the acid, esters of IA are less active than the corresponding acid, and esters of NA are inactive. IA-amide and NA-amide, and dichloro-phenoxyacetic acid, are but very slightly active. NO, its ethyl ester, and naphthoxypropionic acid are completely inactive. When applied in agar to intact coleoptiles, IA, IB and NA are completely inactive. When blocks of lanolin rather than agar are applied to decapitated coleoptiles, 10 to 50 times the conc. of IA, IB and NA must be used to give threshold curvatures. In agar, the relative activities of IA, IB and NA are 100:5:19; in lanolin, 100:11:11. When applied in lanolin to intact coleoptiles, IA, IB and NA have the same activity as when applied to decapitated coleoptiles, i.e., threshold concs. are the same whether the coleoptiles are intact or decapitated. Levulinic acid is completely inactive in the Avena test, whether applied in lanolin or agar, and has no complementary effect when applied together with IA.

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