Changes in Growth, Auxin- and Ribonucleic Acid Metabolism in Wheat Coleoptile Sections Following Pulse Treatment with Indole-3-Acetic Acid

Growth reactions of wbeat coleoptile sections following a brief pretreament in indole-3-acetic acid (LAA) were studied. The growth versus concentration curves 24 hours after the treatment showed a minimum value surrounded by bigber values. The minimum was never at concentrations lower than 10-5M lAA but it could be found at higher concentrations after short pretreatment periods. The growth versus time curves reveated that the hormone treatment cansed the growth rate initially to increase but later on to decrease. The decrease was followed by a second increase for some treatments. Analysis of IAA content after the pretreatment showed that the attered growth patterns could be ascribed to declining auxin content with time, but not to thc actual concentration in the sections. The results indicate that the metabolic activation brought about by IAA leads to its own disappearance. Such a phenomenon was mirroretl in effects of IAA on hte net synthesis of ribonucleic acid.