Oxidation of Indoleacetic Acid by Quackgrass Rhizomes.

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Abstract
Quackgrass rhizomes contain an indole acetic acid oxidase whose characteristics and cofactor requirements, for manganese and a phenolic compound, are similar to those reported for the enzyme from other plants. Rhizomes contain an inhibitor(s) which causes a lag period in IAA oxidation. Length of the inhibition period increases disproportionately (approximately exponentially) as the concentration of the inhibitor is increased. The inhibitor could be removed from extracts of fresher samples of lyophilized rhizomes by dialysis; extracts from aged samples retained the inhibitor even after prolonged dialysis. Inhibition does not appear to be associated with the complex polysaccharide present in the rhizomes or its monosaccharide components. The inhibitor remained in the aqueous phase when solutions of the inhibitor were extracted with ether. Total IAA oxidase activity of the quackgrass rhizomes showed a seasonal variation, but the specific activity remained virtually constant during the same period. Data indicate that variations in IAA oxidase activity are closely associated with general changes in the nitrogenous constituents of the rhizome tissue. IAA oxidase activity decrease and the inhibitor increase occur at the same time. If these effects are operative in vivo, there will be less IAA oxidation as the season progresses.