Abstract
The apical parts of plant stems and roots under elongation growth often exhibit circular or elliptical trajectory, known as circumnutation. In azuki bean epicotyls under circumnutation, the bending zone in each epicotyl is always located at around a transition from the elongation region to the mature region. The changes in the orientation of cortical microtubules along the outer tangential walls of epidermal cells did not seem to be a precedent cause of the bending. On the other hand, auxin polar transport inhibitors or IAA substantially increased the period of circumnutation. Higher radioactivity from 3H-IAA, applied as a lanolin ring, was detected in the pre-concave half of the bending zone compared with the pre-convex half. In the pre-concave side of the epicotyl, the elongation of epidermal cells transiently ceased before cells enter the bending zone and it rapidly recovered when cells leave the bending zone.
