The destruction of indole-3-acetic acid by plant tissues

Citation

Goldacre, Peter L. (1953) The destruction of indole-3-acetic acid by plant tissues. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/G9FF-M178. https://resolver.caltech.edu/CaltechETD:etd-05012003-110235

Abstract

This paper concerns those systems present in the epicotyls of eliolated pea seedlings which inactivate the plant hormone indole-3-acetic acid (I.A.A.). It consists of two sections which deal with (a) the enzyme system collectively known as I.A.A. oxidase and (b) a group of dialyzable substances which sensitize the photodestruction of I.A.A.

I.A.A. oxidase, which behaves as a flavoprotein coupled to a peroxidase is shown to have a partial cofactor requirement. Two alternative systems are postulated. The two systems are differentiated on the basis of their response to Mn++ and to 2,4-dichlorophenol (D.C.P.) and by their change in relative concentrations upon exposure of the seedlings to red light. D.C.P. is shown to increase the activity of I.A.A. oxidase at low concentrations. The mechanism of the effect is studied in detail. Although D.C.P. is a powerful inhibitor of catalase, which inhibits I.A.A. oxidase, it is concluded that the enhancement of I.A.A. oxidase by D.C.P. is not due to its inhibition of catalase. Probably D.C.P. is acting similarly to the native cofactor. D.C.P. increases the in vivo destruction of I.A.A. by some tissues, not by others. It is suggested as a useful tool for studying altered I.A.A. level in a tissue.

The dialyzate from epicotyl brei contains at least four components which sensitize the inactivation of I.A.A. in the light but not in the dark. Blue light is the most effective. The kinetics of the action of the dialyzate has been studied. The active material resides principally in the buds. Preliminary methods of purification have been explored. Some possible physiological roles of the I.A.A. oxidase and the dialyzate have been discussed

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