Riboflavin-Sensitized Photoöxidation of Indoleacetic Acid and Related Compounds

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Abstract
In in vitro studies it was found that riboflavin can sensitize the photooxidation of various indole-con-taining compounds, including the plant growth hormone indole-acetic acid. Under the conditions studied, the reaction goes to completion in 1 hr. Kinetic studies indicate that it is first-order. The reaction requires oxygen. Warburg manometric studies indicate that approximately 1 mol O2 is absorbed and 1 mol CO2 is liberated per mol indoleacetic acid oxidized. The nature of the oxidation product is as yet unknown. The reaction proceeds best at the lower pH values tested, suggesting that the undis-sociated IAA molecule reacts more quickly than the indoleacetic ion. The reaction rate is somewhat accelerated by an increase in temp. Riboflavin analogs work more slowly than riboflavin, or not at all. All indole-containing compounds tested reacted. It is sug-gested that riboflavin-sensitized photo-inactivation of auxin may be an important phenomenon in the normal physiology of the plant.