Enzymatic Hydrolysis of Indoleacetonitrile

Abstract

THAT the growth-promoting action of indole-3-acetonitrile is exerted on some plants but not on others is due to its conversion in the susceptible plants to indoleacetic acid^1,2. The bioassays which made possible the original discovery of indoleacetonitrile in Brassica ^3,4 were made on Avena coleoptiles, which were found^1,2 to carry out the conversion powerfully. Coleoptiles of Zea mays evidently make the conversion weakly, seedlings of Lupinus or Pisum scarcely at all¹. These facts suggested the presence in some plants of an enzyme system which carries out the conversion, and preliminary experiments led to the demonstration that a cell-free plant juice from Avena coleoptiles has this ability. For further work a number of plants was studied as possible sources of the enzyme, and leaves of Avena and Hordeum were found very active. Most of the subsequent experiments, including those described here, have been made with barley leaves and stems, Breck's six-row variety. The activity was assayed by incubating the juice with a known quantity of synthetic indoleacetonitrile for 4 hr., then acidifying the solution to pH 2.8 with H₃PO₄, shaking out with ether, treating the ethereal solution with saturated sodium bicarbonate and acidifying the latter and re-extracting. The ether extract was taken up in water and its indoleacetic acid content determined by the Salkowski reaction⁵. Earlier experiments had shown good agreement of the Salkowski indoleacetic acid determinations with results obtained from pea curvature and pea straight-growth bioassays, and with estimates from paper chromatograms.