The influence of acropetally transported indoleacetic acid on the geotropism of intact pea roots and its modification by 2, 3, 5-triiodobenzoic acid

The geotropic response of horizontal intact pea seedling roots was rapidly influenced by indoIe-3-acetic acid (IAA), which was applied in narrow rings of lanolin paste a few cm from the apex. The applied auxin thus likely was transported in the acropetal direction in these roots. The influence of IAA was strongly reduced when 2, 3, 5-triiodobenzoic acid (TIBA) was applied to the roots at the apical side of the IAA-ring. When TIBA was applied alone at various distances from the apex of the horizontal roots it also inhibited the geotropic curvature. The transport of auxin in the apical region of horizontal roots probably occurred both in the acropetal and in the basipetal direction.