Polarity of Auxin Movement by Basipetal Transport'

Sikmninarv. The polar, basipetal transport of indoleacetic acid helps to mlainitain l)olarity of auxin movement in coleoptiles of Azcna sativa L. by opposing acropetal diffusion. This conclusion is supported by 3 different kinds of experiments. In all 3 experiments, sections took up 14C carboxyl-labeled indole-3-acetic acid anaerobically, anid the distribution of auxin within all sections was similar at the end of uptake. 1) After basal donors were replaced by receivers, basipetal movement was more rapid in air than nitrogen. This increase in basipetal movement is attributed to transport, and occurred within 15 miniutes after sections were transferred to air. Apparently the basipetal transport has ready access to auxin diffusing within the sectioil. 2) After basal donors were removed and the sections were suspended without receivers, acropetal moveement was less in aerobic than anaerobic sections. 3) After apical donors were replaced by apical receivers. acropetal movement was again less in sections made aerobic. The decrease in acropetal movement in air equalled the amounit of auxin moved basipetally by transport. The latter 2 experiments show that basipetal transport reduces the net acropetal flux of auxin.