Mediation of geotropic response by lateral transport of auxin

Abstract

The distribution of auxin during geotropic stimulation of corn coleoptiles has been determined by means of the Avena test. It has been verified that equal amounts of auxin diffuse out from vertical and from horizontal coleoptile tips, and that the lower halves of partially split coleoptile tips release a larger amount of auxin than do the upper halves. When coleoptile tips are completely bisected prior to stimulation, however, the same quantity of auxin is obtained from each half. The simplest interpretation of these results is that auxin, or possibly an auxin, or possibly an auxin precursor, is translocated from the upper to the lower side of a stimulated coleoptile.