The IAA-oxidase system of citrus roots

Abstract

The activity of indoleacetic acid oxidase in citrus plants (roots of mature trees and roots and stems of seedlings) was demonstrated. The interrelationships between 2,4-dichlorophenol, Mn⁺⁺ and the enzymatic activity were examined. The presence of Mn⁺⁺ was not found necessary, even in dialyzed enzyme reaction mixtures. However, Mn⁺⁺ promoted the enzymatic activity at the very high concentration of 10^-1M. The inhibitory effect induced by excessive amounts of 2,4-dichlorophenol (10^-3 M) was removed in the presence of Mn⁺⁺. The enzyme showed a specificity to IAA as compared with other synthetic auxins in a wheat coleoptile bioassay. Moreover, the enzyme acted selectively on some endogenous auxins found in citrus tissues. The existence of endogenous inhibitors in stems and cofactors in roots was also demonstrated.