THE PATHWAY OF TRANSPORT OF APPLIED INDOLYL‐ACETIC ACID THROUGH INTERNODE SEGMENTS

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Abstract
Summary: Helianthus internode segments were fitted with apical donor blocks containing [14C]IAA and [3H]sucrose, and plain agar basal receiver blocks. After transport, donors, tissue and receivers were oxidized in an ‘Oxymat’ and 14C and 3H counted separately. Ageing the segments before transport, or pretreatment with TIBA, greatly reduced the amount of 14C in the receivers, but had no effect on the 3H count.Profiles of 14C were determined after transport of [14 C]IAA through similar segments ringed to various depths, or with the pith interrupted. Interruption of the vascular bundles, but not of the pith, caused accumulation of I4C above the cut in segments transporting IAA basipetally; no accumulation was caused by ringing segments transporting IAA acropetally.It is concluded that active polar transport of IAA takes place in or near the phloem, but by a different mechanism from the one involved in sucrose transport through the phloem of intact plants.