Auxin Transport in Roots VI. MOVEMENT OF IAA THROUGH DIFFERENT ZONES OF ZEA ROOTS

The movement of IAA through 6-mm segments excised 1 mm, 7 mm, and 13 mm behind the apex of the primary root of Zea mays seedlings has been investigated at temperatures between 10 and 25 °C. In all segments, and at all temperatures, the movement of IAA was polarized acropetally, more IAA being found in apical receiver blocks than in basal ones after transport periods of up to 24 h. The amounts of IAA which moved acropetally through a segment decreased as the segment was taken at an increasing distance behind the root apex. Similarly, at least after transport periods of 8 h, more IAA moved basipetally through the apical segment than through the basal ones. At 10 °C the velocity of acropetal movement was similar in all three segments, but the acropetal _/Zi<a; was greatest in the apical segment and smallest in the most basal one. The same situation appears to exist at the other temperatures. The flux and velocity of the acropetal movement of IAA through a 6-mm segment taken 7 mm behind the apex of the root were similar to those previously reported for the acropetal movement through a 12-mm segment excised 1 mm behind the apex. The smaller amounts of IAA which move acropetally through longer root segments are therefore attributable to a limitation of the flux in the most basal regions of the segment