Metabolism of Tryptophan in Petioles of Coleus

Abstract

Auxin precursors retard abscission when applied to debladed petioles of Coleus blumei Benth. The D and L forms of tryptophan are equally effective in retarding abscission. Tryptamine is more effective than tryptophan. Both compounds apparently are converted to auxin through an aldehyde intermediate. A major pathway of tryptophan metabolism probably proceeds through tryptamine, as can be demonstrated by the use of amine oxidase inhibitors in the petiole tissue. Cell free preparations of the tissues metabolize tryptophan-1-C14 with the release of CO2. The rate of tryptophan metabolism in abscission tissue is 5 times that in distal petiole tissue. Radioactivity is associated with basic indole conversion products as well as with neutral and acidic fractions. The radioactivity is most concentrated in the neutral fraction. Thus, the Coleus petiole itself is capable of producing auxin.