The IAA-oxidase system of citrus roots

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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.