| Summary: | The enzymatic breakdown of indoleacetic acid in the presence of aqueous pea root extracts containing an "indoleacetic acid-oxidase" system was studied. A method based on the "Salkowski" colour reaction was used for the estimation of residual indoleacetic acid. A comparison was made between the "indoleacetic acid-oxidase" activity of extracts made from the roots of plants grown in water and the activity of extracts made from the roots of plants grown in a solution of indoleacetic acid. It was found that the activity of the extracts from the "indoleacetic acid-grown" roots was higher than that of the extracts from the "water-grown" roots. Thus the "maximum rate attained in the reaction" was greater, and the "length of the lag period" shorter, when extracts of the "indoleacetic acid-grown" roots were used. Further, the relationship between the length of the lag period and the maximum rate attained appeared to be slightly different for reaction mixtures containing the two types of extract. The inhibitory activity of solutions prepared from the "water-grown" root extracts and the "indoleacetic acid-grown" root extracts by i. boiling, ii. seitz filtration, or iii. ultrafiltration, wasdetermined. The inhibitor solutions prepared from the "indoleaceticacid-grown" root extracts were always found to be less active thanthe corresponding inhibitor solutions prepared from the "water-grown" root extracts. It was thought that this difference in inhibitorlevel may have accounted for the different level of "enzyme activity"demonstrated for the extracts of the "water-grown" and "indoleacetic acid-grown" roots. The significance of the enhanced "indoleacetic acid-oxidase" activity of "indoleacetic acid-grown" root extracts was discussedin relation to the hypothesis of adaptive enzyme formation. It was concluded that the enzyme was not formed adaptively in the pea root tissues in response to the applied indoleacetic acid.
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