Studies on the Auxin Metabolism of Some Cereal Crops under Germination and Seedling Growth : I. Some characteristics of IAA-oxidizing enzyme existing in wheat seedlings.

[摘要] Some characteristics of IAA-oxidizing enzyme existing in dark-grown wheat seedlings were studied, and the results obtained were summarized as follows: After demonstrating the existence of IAA-oxidizing action in dark-grown wheat seedlings, the crude- and dialyzed homogenates were prepared from root, coleoptile and plumule. Then, their IAA-oxidizing and guaiacol-peroxidizing activities were determined and compared with each other. The dialysed enzyme preparation from wheat seedlings showed a considerably high IAA-oxidizing activity. Descending order of this enzyme activity was root, coleoptile and plumule, and pH 4.5, 5.0, and 5.5 were the optimum pH value in root, coleoptile and plumule respectively. Similar results were obtained in the activity of peroxidase from the same source. There was, however, a eminent difference between the crude and dialysed enzyme preparation in the mode of action that the crude enzyme preparation is lacking in IAA-oxidizing activity in spite of its high peroxidase activity. It may be, therefore, concluded that the lack of IAA-oxidizing activity of the crude preparation is due to the existence of some dialysable, heat-stable inhibitors in the preparation. In order to clarify the caracteristics of IAA-oxidizing enzyme furthermore, the authers have undertaken some experiments and obtained the following results. IAA-oxidizing activity of the dialysed preparation was inactivated by heat-treatment as the exactly same as the activity of peroxidase in the same preparation, and IAA-oxidizing activity of the crude preparation was considerably promoted by addition of both Mn++ and DCP, while the activity of the dialysed preparation was inhibited by added Mn++ and was promoted by added DCP. In the mode of inhibitory action of some enzyme inhibitors added, there were considerable differences between IAA-oxidation and guaiacol-peroxidation. A comparatively low concentration, 10-5M of H2O2, showed a little promotion of IAA-oxidizing activity in the dialysed preperation, but the activity was greatly inhibited by a much higher concentration, 10-4M of H2O2, and catalase showed little effect on the activity of the same preparation. From the above-mentioned results, it may be concluded that IAA-oxidizing enzyme existing in dark-grown wheat seedlings is a peroxidase and there are some differences between IAA-oxidation and guaiacol-peroxidation in the reaction mechanism. Furthermore, from the results concerning the effects of catalase and H2O2, it is suggested that IAA may be oxidized by wheat seedling peroxidase through the same reaction mechanism as the scheme presented by YAMAZAKI and SOUZU (1958). ADDENDUM: Since this manuscript went to press, we have noticed that the inhibitory effect of Mn++ on IAA-oxidizing activity in the dialysed enzyme preparation may be due to the chelating effect of citrate in McIlvaine's (phosphate-citric acid) buffer used, and that this phenomenon has been already described in the following papers. Kenten, R. H. 1955. The oxidation of indolyl-3-acetic acid by waxpod bean root sap and peroxidase systems. Biochem. J. 59 : 110-121. Stutz, R. E. 1957. The indole-3-acetic acid oxidase of Lupinus albus L. Plant Physiol. 32 : 31-39.

[学科分类] 农业科学（综合）