Influences of Gibberellic Acid on Metabolism of Indoleacetic Acid, Acetate, and Glucose in Roots of Higher Plants

The major effects of the gibberellins (GA) on plants have been reviewed recently (13, 14) but no definite linkage with any metabolic pathway has been established. In their study of photosynthesis in gibberellin treated leaves Haber and Tolbert (8) concluded that gibberellic acid neither enhanced the rate of CO2 fixation per unit of leaf tissue nor altered the general pathways of short time metabolism of the newly fixed C140 in the sugars, organic acids, and amino acid products. In long term experiments, great charnges in carbohydrate constituents of gibberellin treated plants have been reported (4, 9). Inhibition in the level of indoleacetic acid oxidase by gibberellic acid has been reported by Pilet (12). However, Brian and Hemming (5) did not find a similar effect in their system. Recently, Galston and Warburg (7) suggested a possible action of gibberellin through an auxin-sparing mechanism by way of the formation of IAA oxidase inhibitor. It is the purpose of this paper to describe the results of experiments on the influence of GA on plant metabolism. In the method used, plant tissue was first pre-treated with GA and then incubated with a selected isotopically labeled substrate. Samples of the tissue were then harvested after several hours of incubation. The influence of GA on the metabolism of the material was determined bv comparing the extents of the labeled atoms whicl have been metabolized and incorporated into other compouncls between the control and treated tissues.