DIFFERENT COMPONENTS OF THE MOVEMENT AND THE AREAS OF RETENTION OF LABELED MOLECULES AFTER APPLICATION OF [H-3]-LABELED INDOLYL-ACETIC ACID TO THE APICAL BUD OF VICIA-FABA

After application of [3H]‐auxin (0.8 nmol) to a young leaf of Vicia faba L. cv. Aguadulce. about 6% (1.1 × 10‐2 nmol) of applied IAA enters the stem during the first 6 h of transport. This corresponds to a [3H]‐auxin flux which is probably not very different from the endogenous flux. A wave of [3H]‐ auxin moves down to the roots mainly among preferential pathways situated in the vascular bundle. This movement is accompanied and followed by certain events: (I) In the upper part of the stem, some radioactive molecules leave the pathways of polar transport and enter the young leaves near the donor leaf. (2) In other parts of the stem, the auxin transport is highly polar. As the peak of the wave approaches and passes a node with an axillary bud. and for a few hours afterwards, there is no clearly detectable radioactivity in this bud, although the nodal tissues are very radioactive. (3) A retention of labelled molecules often occurs in the nodes. (4) Retention of label is regularly seen in the basal part of the first internode and in the hypocotyl, which together form that part of the axis where Ifle highly inhibited cotyledonary buds are found. This retention is still manifest a week after the downward transport of [3H]‐auxin. (5) After 48 h. a high proportion (about 45%) of the [3H]‐auxin exported by the donor leaf is found in the roots. (6) Subsequently, a part of the label returns to the upper parts of the plant, and especially to the leaves, where it normally appears to be immobilized. (7) As time goes on some labelled molecules, probably coming from different areas, enter the axillary buds. Copyright © 1979, Wiley Blackwell. All rights reserved