Abstract. Aotivity of indoleacetic acid oxidase in partially purified extracts from cotton is stimtulated by small amounts of malate, suocinate, fumarate, and other plant acids. The stimulation is apparently due to inhibition of catalase, which is detectable in certain preparations. The 4ag phase of indeleacetic acid oxidation by crude preparations is eliminated by steps in processing which oonceivably either denatures or dilutes catalse, or concentrates inhibitors to catalase.IAA-oxidase is inhibited int vitro by catalase (4, 5, 11), polyphenols (1, 3, 7, 14), various inhibitors and substrates of peroxidase (6,20), and by unidentified constituents of plant extracts (13,19). A number of phenols act in vitro either as inhibitors or co-factors, and a rather extensive literature provides a tacit support for the function of phenols in these roles in the plant.The possibility of regulation of IAA-oxidase by catalase in vivo has received surprisingly little emphasis. This has probably followed the observation of Goldacre et al. l(6) that phenols stimulate IAA-oxidase of peas in the absence of catalase. In efforts to partially purify IAA-oxidase from cotton roots, Lane (12) found that the protein (enzyme) fraction was separated from certain plant acids with a complete loss of IAA-oxidase activity. Addition of a small amount of any one of several organic acids restored activity completely.Noting that these same acids are inhibitors of catalase, we determined the effect of several acids on activities of catalase, peroxidase and IAA-oxidase in extracts of cotton.
Results and DiscussionPlant Ciiltu(re. ,tmoles in 0.1 ml of water. Except whein noted, 2,4-dichlorophenol was not lused. All assays were conducted using 1 ml of enzyme soluttion, regardless of extent of concentration.Catalase. Decomposition of 110., was monlitored spectrophotometrically at 240 nm at 250, The reaction mixture contained 2 ml plant extract at appropriate dilution and 1 ml 0.059 M H.202 in 0,05 M phos,phate buffer, pH 7.0.For studies on the inhibition of catalase activitv by organic acids and 2,4-dichlorophenol, 3 tumoles of these compounds were added to the above in 0.1 ml. Controls contained 0.1 ml water. Initial rates of reaction were plotted froml optical density readings taken at 10 sec intervals for 2 mimi.Peroxidase. Appearanice of 8-aminoqu-i,noline oxidation prodtuct was monitored spectrophotometri-1699 www.plantphysiol.org on May 10, 2018 -Published by Downloaded from