The specificity of auxin transport in intact pea seedlings (Pisum sativum L.)

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Abstract
When eight 14C-labelled auxin and non-auxin compounds were applied to the apical buds of intact dwarf pea seedlings (Pisum sativum L.), only [1-14C]indoleacetic acid ([14C]IAA) and α-[1-14C] naphthaleneacetic acid ([14C]NAA) underwent appreciable basipetal transport during the first 24 h; over a longer period (72 h) considerable basipetal transport of the auxin [1-14C]2,4-dichlorophenoxyacetic acid ([14C]2,4-D) also occurred, but at a very much lower velocity (ca. 1.4–2.2 mm·h-1). The movement of 2,4-D possessed many of the characteristics of a typical auxin transport. During uptake and transport IAA and NAA were extensively metabolised to the corresponding aspartates, and to ethanol-insoluble/NaOH-soluble compounds; little metabolism of 2,4-D was observed. None of the non-auxin compounds applied (sorbose, sucrose, leucine, adenine and kinetin) underwent appreciable basipetal transport from the apical bud. All but sorbose were extensively metabolised by the apical tissues. Little metabolism of sorbose itself was detected. The results suggest that the long-distance basipetal auxin transport system from the apical bud of intact plants is specific for auxins; the specificity may result from the affinity of auxins for specific transport sites.