Auxin transport in intact pea seedlings (Pisum sativum L.): The inhibition of transport by 2,3,5-triiodobenzoic acid

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Abstract
The application of 2,3,5-triiodobenzoic acid (TIBA, 10 mg·g-1 in lanolin) to the stem of intact pea seedlings (Pisum sativum L.) inhibited the basipetal transport of 14C from indoleacetic acid-1-14C (IAA-1-14C) applied to the apical bud, but not the transport of 14C in the phloem following the application of IAA-1-14C or sucrose-14C to mature foliage leaves. It was concluded that fundamentally different mechanisms of auxin transport operate in these two pathways. When TIBA was applied at the same time as, or 3.0 h after, the application of IAA-1-14C to the apical bud, 14C accumulated in the TIBA-treated and higher internodes; when TIBA was applied 24.0 h before the IAA-1-14C, transport in the stem above the TIBA-treated internode was considerably reduced. TIBA treatments did not consistently influence the total recovery of 14C, or the conversion of free IAA to indoleaspartic acid (IAAsp). These results are discussed in relation to the possible mechanism by which TIBA inhibits auxin transport,. Attention is drawn to the need for more detailed studies of the role of the phloem in the transport of endogenous auxin in the intact plant.