Transport of shoot- and cotyledon-applied indole-3-acetic acid to Vicia faba root

To clarify the participation of indole-3-acetic acid (IAA) originating from the shoot in root growth regulation and the mechanism of IAA translocation from shoot to root, the movement of 14C-IAA which was applied to the epicotyl or the cotyledon of Vicia faba seedlings was investigated. The radioactivity of IAA applied to the cotyledon moved faster to the root tip than that applied to the epicotyl. On the basis of the effect of 2,3,5-triiodobenzoic acid on IAA movement, a comparison with 14C-glucose movement and autoradiographic examination, the nature of IAA movement was concluded to be polar transport from the epicotyl to the basal part of the roots, while IAA movement from the epicotyl to the cotyledon, from the basal part of roots to the apical part, and from the cotyledon to the epicotyl and to the root took place in the phloem. The radioactivity from 14C-IAA applied to the cotyledon accumulated in lateral root primordia and vascular bundles. These facts suggest that IAA produced in cotyledons may participate in the regulation of Vicia root development.