Auxin Activity of Isatin and Oxindole-3-Acetic Acid.

Most workers have found that oxindoles are inactive as auxins or as auxin antagonists. For example, Thimann (44) working with straight growth of Az'ena coleoptile cylinders anid Pisitm stem sectiolns, and with growth curvature of slit Pistni stem sections, found the following 6 compounds to be without effect at concentraticns up to 30 mg/liter, both in the absence and presence of IAA at concentrations up to 5 mg/liter: oxindole-3-acetonitrile, oxindole-3pyruvic oxime, oxindolene-3-acetonitrile, oxindolene3-pyruvic acid, 3-dehydrodioxindole and 3-methyl dioxinidole. In this paper, we would like to report on the considerable growth activity elicited by isatin (indole-2, 3-dione) alnd oxindole-3-acetic acid (fig 1) compounids which, on the basis of past literature, would have been expected to he inactive.