Auxin transport in Avena: I. Indoleacetic Acid-C distributions and speeds.

Measurements have been made on the initial stages of the transport of carbon-14-labeled indoleacetic acid in the coleoptile of Avena sativa L. Concentrations of mobile and immobilized indoleacetic acid are related to both distance and time during the first 2 hours after application of the indoleacetic acid at several concentrations to the top of the decapitated coleoptile.At the lowest concentration of indoleacetic acid applied (0.3 mum), the graphs of concentration against distance are linear from near the top of the coleoptile to the front of the indoleacetic acid stream. The indoleacetic acid possesses a definite front moving at constant speed. In the region of the front the graphs are linear even with concentrations above 1 mum applied.A large proportion of the mobile indoleacetic acid in the coleoptile does not move with the speed of the front of the stream. The rate of immobilization of indoleacetic acid by a cell increases with time after the arrival of the indoleacetic acid. Each cell must pass on to the next nearly all the indoleacetic acid it initially receives.Effects of indoleacetic acid application for a short time are investigated, as is the effect of triiodobenzoic acid on indoleacetic acid transport. It is deduced that diffusion does not play a major part in the normal transport of auxin in the coleoptile.