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It was first suggested by Tang and Bonner (14) that indole-3-carboxaldehyde is the product of the oxidative degradation of indole-3-acetic acid (IAA) by crude enzyme preparations from etiolated pea seedlings. Using the more active bean root enzyme, Wagenknecht and Burris (15) attempted without success to obtain the 2,4-dinitropheny1hydrazone of the aldehyde. On the basis of chromatographic data, Racusen (9) reports that the pea enzyme forms small amounts of the aldehyde. More MIanningf and Galston (7) have reported the formation in the pea system of two products having high Rf values and giving qualitative color tests which indicate a similarity to our products # 4 and # 5 (see below). They were unable to demonstrate the formation of indole-3-carboxaldehyde, and also ruled out ortho-formamidoacetophenone, ortho-aminoacetophenone, and 4-hydroxyquinoline as major end products, although they believe that the indole ring is ruptured.Chromatographic separation and spectrophotometric examination of the products of the IAA oxidase-peroxidase system from Lupinus albus L. (13) gave no indication that the aldehyde was formed; likewise, the results obtained when the chromatograms were tested with 2,4-dinitrophenylhydrazine hydrochloride, modified Salkowski (3), and Ehrlich reagent suggested the absence of the aldehyde. In view of the conflicting results, attempts were made to suplement the purified IAA oxidase with the auxiliary enzyme systems presumed to be present in the crude enzyme preparations employed in the early investigations. The present report is concerned with the coupling of the oxidase system to the cytochrome oxidase system. Under these conditions the formation of indole-3-carboxaldehyde as a major reaction product was observed.Subsequent reexamination of the reaction products from the oxidase-peroxidase system, particularly those freshly prepared from etiolated lupine hypocotyls, the oxidation mechanism, indole-3-carboxylic acid and a number of substituted indole-3-acetic acid derivatives were tested both with the oxidase-peroxidase system alone and with the added cytochrome system. It is of interest to note that since this paper was submitted, Jones and Taylor (5) have reported the isolation of both indole-3-carboxaldehyde and indole-3-carboxvlic acid from cabbage extracts. MATERIALS AND METHODSPreparation and purification of the IAA oxidase from Lupinus albus L. has been previously described (13). The course of the oxidation of IAA was followed with the Warburg manometric apparatus under the conditions outlined earlier (13) except where 0.4 M tris-(hy-droxymethyl)-aminomethane buffer at pH 7.2 was uised in an attempt to approach the pH optimum of the cytochrome oxidase system and still maintain IAA oxidase activity. Under these conditions a small amount of phosphate, 4 micromoles per flask, was added for optimum IAA oxidase activity. The normal 3-ml reaction mixture was enzyme; 1 ml 0.4 M orthophosphate buffer, pH 6.3; 0.3 micromole MInCl,; 0.3 micromole soditim-2,4-dichlorophenolate; (in the main com...

Recent reports from several laboratories (1,6,8,12) on the effect of gibberellin treatment upon indole-3-acetic acid (IAA) In this paper we have investigated the growth stimulation and IAA oxidase activity in intact lupine plants which had been treated over an extended period with low doses of gibberellic acid (GA) and cultured under two different daylengths. A preliminary report of this work has been presented (12). The results support the views proposed by Vlitos and Meudt (15) and Galston and Warburg (3) that growth stimulation by GA is probably mediated through an auxin-sparing mechanism. Recently Philips and coworkers (7) have presented evidence that GA does not function by an auxin-sparing mechanism but forms a growth-stimulating complex which acts both as an auxin and gibberellin-like compound. It is suggested that had the other investigators (1, 6) assayed tissues which had been treated with GA over a longer period of time that they may have observed a reduction in IAA oxidase activity.

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