[Translocation of labeled indolyl-3-acetic acid in sieve tubes of Vicia faba]

Abstract

Young plants of Vicia faba fed through the first primary leaf with a 5\10(-3) mol solution of indolylacetic acid (IAA) show a bending of the stem above the treated leaf after a certain amount of time. The movement of the growth substance is several times faster than it is in the parenchyma. Some hours later, the stem growths upright again.When labeled IAA [indolyl-3-(acetic acid-2-(14)C)] is used, the autoradiographs of the plants show labeled material in the stem, in roots, and in the youngest leaves; older leaves do not incorporate labeled material. The distribution pattern is similar when the tracer is applied to the third primary leaf.The extract of the stem contains labeled IAA and 2 water-soluble derivates of IAA. Upon hydrolysis with HCl the latter yield labeled IAA. One of these substances seems to be indolylacetyl-aspartic acid.Aphids (Acyrthosiphon pisum; Neomyzus circumflexus) feeding on the stem of a plant treated with labeled IAA on the 1. primary leaf produce honey dew which contains IAA as the only labeled substance; neither of the other labeled substances found in the extract occurs in the honey dew. The possibility that the IAA of the honey dew is produced by the splitting of one or both of the unknown labeled substances of the extract could be excluded by artificial feeding of aphids on a diet solution containing those substances. Honey dew from aphids fed in this way contained both substances unchanged.These findings indicate that applied IAA moves in the sieve tubes. The other labeled IAA-derivatives of the extract are phloem-immobile; they obviously are formed in parenchyma cells.