Rhythmic Differences in the Basipetal Movement of Indoleacetic Acid between Separated Upper and Lower Halves of Geotropically Stimulated Corn Coleoptiles

Abstract

Rhythmic fluctuation in the basipetal movement of auxin occurs in corn (Zea mays) coleoptiles oriented either in the vertical or in the horizontal position. This periodicity of transport rate varies from region to region in a horizontal coleoptile. Between an upper and lower half coleoptile (with respect to gravity), the comparable regions in the coleoptile do not exhibit similar periods. The velocity of transport also varies from region to region along a geostimulated coleoptile. In the upper half coleoptile, the velocities are 29 millimeters per hour (tip), 8 millimeters per hour (mid), and 30 millimeters per hour (base); in the lower, 41 millimeters per hour (tip), 12 millimeters per hour (mid) and 12 millimeters per hour (base).During the first 24 minutes of transport, there is a reduction of basipetal movement of (14)C-indoleacetic acid in the lower half coleoptile. This may be causally related to the initial downward geotropic curvature in oat and corn coleoptiles reported by others. However, about 30 minutes after donor removal a significant reduction of basipetal transport of indoleacetic acid occurs in the upper half coleoptiles.