Plant Physiol. Drug Metab Dispos
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Plant Physiology 73:1-5 (1983)
© 1983 American Society of Plant Biologists

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Articles

In Vivo Measurement of Indole-3-acetic Acid Decarboxylation in Aging Coleus Petiole Sections

Thomas Brennan and William P. Jacobs

Department of Biology, Dickinson College, Carlisle, Pennsylvania 17013, Department of Biology, Princeton University, Princeton, New Jersey 08544

The concentration of indoleacetic acid (IAA) in plant tissues is regulated, in part, by its rate of decarboxylation. However, the commonly used in vitro assays for IAA oxidase may not accurately reflect total in vivo decarboxylation rates. A method for measuring in vivo decarboxylation was utilized in which 14CO2 is collected following uptake of [1-14C]IAA by excised tissue sections. After a 30-minute equilibration period, the evolution of 14CO2 was found to follow an approximately linear course with respect to both time and tissue weight.

Decarboxylation rates were measured by this method in petiole sections of the Princeton clone of Coleus blumei Benth. Both the 14CO2 evolved per milligram tissue and the percent of [1-14C]IAA uptake decarboxylated were highest in sections from the youngest petioles tested, and declined in the older tissue. Thin layer chromatography of acetonitrile extracts from the [1-14C]IAA-treated petioles showed a decreasing amount of free IAA and an increase at the retardation factor of indoleacetylaspartate in the older sections. The decreased decarboxylation rates in the older petioles may be attributable to a generally lower metabolic rate and increased protection of the IAA by conjugation.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1983 by the American Society of Plant Biologists