The Effect of Catalase, Riboflavin and Light on the Oxidation of Indoleacetic Acid.

Catalase mediates the decarboxylation and oxidation of indoleacetic acid by acting peroxidatically in a reaction sequence which involves: (a) initiation by manganic ions, (b) peroxide formation, (c) catalysed peroxidation of organic hydrogen donors, (d) manganese oxidation. The peroxidatic activity of catalase is inhibited during the oxidation but the catalatic activity remains unimpared. Light has no effect on the oxidation of indoleacetic acid by catalase systems unless certain inhibitors are present. Undialysed catalase preparations from beef liver contain a photolabite thermostable inhibitor. Ribo-flavinphosphate retards IAA oxidation and light of the blue region over-comes its effect. Light and riboflavinphosphate together do not augment the rate of IAA oxidation beyond that in darkness in the absence of riboflavin. Evidence in favour of the operation of this system in the intact plant is summarized. It is suggested that riboflavin promotes growth by inhibiting indoleacetic acid destruction. Light overcomes the protective effect of riboflavin phosphate in vitro and may thereby inhibit growth. [ABSTRACT FROM AUTHOR]