Abstract
Evidence is presented that IAA is oxidized with the liberation of hydrogen peroxide, and that the rate of oxidation is limited by a light-activated step. Methyl umbelliferone, maleic hydrazide, and 2,4-D stimulate IAA oxidation, presumably by accelerating the light-activated step. The stimulatory action of all three substances is overcome to a greater or less extent by scopoletin, which competitively inhibits the oxidation of IAA. It is suggested that maleic hydrazide and methyl umbelliferone may inhibit growth by causing an excessive oxidation of IAA. The importance of fluorescent coumarin derivatives on the photooxidation of IAA in vivo is discussed.
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