Transient Effects of Indoleacetic Acid on the Absorption and Utilization of Radioactive Acetate by Pea Stem Slices

When pea stem slices are pretreated in ia solution of unlabeled potassium acetate and IAA then exposed briefly to radioactive acetate the incorporation of radioactivity into various celluilar constituents is less th.an that for slices pretreated in potassium acetate only (5). As the length of the pretreatment periood is extended the apparent inhibition becomes progressively greater. This inhibition is evidently a transient effect since IAA at this concentration (2.5 X 10-4 M), in experiments not having a pretreatment phase, is not inhibitory over a short experimental period and,only mildly so over a period of several hours. It was proposed that IAA directs acetate from certain pathways into others leading to an enhanced synthesis of organic acids. This interpretation was rejected when it was discovered that the inhibitory effect on incorporation is accompanied by the accumulation of unassimilated acetate-C14 (6). This finding suggests that dilution of the acetate-C14 by unlabeled acetate taken up during the pretreatment period causes the transient inhibition of incorporation of the ilabel. The effects of IAA on the metabolism of labeled acetate in pea stem sections in nonpretreatment experiments are similar to those produced by 2,4-dichloroephenoxyacetic acid on th.e utilization of acetateC14 by bean stem sections (2).