Transport of ¹⁴C-lableled indoleacetic acid in Vicia root segments

IAA transport in Vicia root segments was investigated for comparison with that in intact roots. Lanolin paste (1-mm-wide ring) or agar blocks (3×3×1.5mm), both containing IAA-2-14C were applied to the surface or a cut end of the root segments, respectively; transported 14C was collected in receiver agar blocks placed on the cut end of the segments. When lanolin paste was applied to 5-mm segments, basipetal transport of IAA predominated over acropetal transport. When agar blocks were applied to 1- and 2-mm segments, the same was true; in longer segments (3 and 5 mm long), however, basipetal movement occurred predominantly at first but was surpassed by acropetal movement after 2–3 hr. Among the segments tested (regions 2–4, 4–6 and 8–10 mm from the tip), the most apical one showed the distinctest predominancy of basipetal movement. The velocities of the acropetal and basipetal movement of the 14C were estimated at 3–3.8 and 8–12 mm/hr, respectively. Autoradiographic study and the experiment in which wire was inserted longitudinally through the central part of the segments showed that basipetal movement occurred mainly through the outer part of the roots and acropetal movement mainly through the central cylinder. The present results were compatible with those obtained previously with intact roots. Some properties of polar movement, such as its specificity, inhibition by TIBA, and dependency on tern eprature are described.