Oxidation of Indoleacetic Acid by Quackgrass Rhizomes.

The enzymatic oxidlation of 3-indoleacetic aci(l (IAA) which was first described in detail by Tang and Bonner (16, 17), has been observed in several types of plants, e.g., fungi (13), ferns (14), monocotyledonous plants (20), and dicotyledonous plants (16, 17, 19). Although differences have been observed in regard to the enzyme's requirement for a phenolic cofactor, and in the pH optimum, the requirement for manganese seems to be general. Interest in the IAA oxidase of quackgrass rhizomes arose from the finding that the rhizomes showed a seasonal variation in bud activity (5). The hypothesis that the bud activity of quackgrass rhizomes may reflect the concentration of IAA in the rhizomes, and that this concentration may be controlled by IAA oxidase was considered. Others have presented evidence both for (4) and against (2) the participation of IAA oxidase in the control of IAA concentration under physiological conditions. In the course of the present study, some characteristics of the IAA oxidase of quackgrass rhizomes have been compared with the IAA oxidase from other sources. The relationship between total nitrogen of the rhizome tissue, IAA oxidase activity, and the protein content of the enzvme extracts is discussed.