Auxin transport in roots

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Abstract
The movement of IAA has been investigated in roots of dark-grown seedlings of Zea mays using IAA-I-14C. With 6-mm segments excised 1 mm below the apex of the root it has been shown that: (a) There is a strictly acropetal flux of IAA through the tissues, the amount of IAA found in an apical receiving block increasing almost linearly with increasing transport period up to about 6–7 hours, but thereafter declining for at least a further 18 hours. The onset of this decline appears to be dependent upon the concentration of IAA in the donor block. (b) The amount of IAA recovered in the apical receiving block increases with increasing concentration of IAA in the donor block over the range from 0.1–10 μM, with transport periods of both 4 and 9 hours. (c) The radioactivity in the receiving block is confined to the IAA molecule. (d) The orientation of the segment with respect to gravity did not significantly affect the acropetal polar flux of IAA in the tissue. With non-decapitated 7-mm root apices it has been found that the presence of the apex has no effect on the strictly acropetal flux of IAA in the tissues, but that it entirely prevented the emergence of IAA into an apical receiving block.