Indoleacetic Acid Oxidase Activity in Two High‐Peroxidase Tomato Mutants

Abstract Homogenates of tomato ( Lycopersicon esculentum Mill.) tissues oxidize IAA at a rate proportional to their peroxidase activity. Moreover, isoproteins with peroxidase activity catalyze also the oxidation of IAA. Two monogenic recessive mutations, olivacea and monstrosa , are involved in the control of the peroxidase‐IAA oxidase activity. In olivacea leaflets this activity is 15 times that of the normal; all the aerial organs of monstrosa show high activities, particularly the midrib. These high activities depend on the enhancement of the organ‐specific isoenzymes and on the derepression of the root isoenzyme band C2. This latter peroxidase‐IAA oxidase band is present in olivacea and monstrosa leaflets, in monstrosa stems and, less intensely stained, in monstrosa midribs. The reduction in length and weight of mutant organs and their epinastic and geotropic‐like behavior are associated with high peroxidase‐IAA oxidase activities and with the derepression of the root‐specific band C2. These results suggest an important role of the peroxidase‐IAA oxidase system in controlling the metric relationships among different organs of the plant. Olivacea and monstrosa are to be viewed as auxin‐related mutations controlling the synthesis of a group of proteins related in function.