| Abstract: | 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 seedlingshas been investigated at temperatures between 10 and 25°C. In all segments, and at all temperatures, the movement of IAAwas polarized acropetally, more IAA being found in apical receiverblocks than in basal ones after transport periods of up to 24h. The amounts of IAA which moved acropetally through a segmentdecreased as the segment was taken at an increasing distancebehind the root apex. Similarly, at least after transport periodsof 8 h, more IAA moved basipetally through the apical segmentthan through the basal ones. At 10°C the velocity of acropetal movement was similar inall three segments, but the acropetbut the acropetal flux wasgreatest in the apical segment and smallest in the most basalone. The same situation appears to exist at the other temperatures. The flux and velocity of the acropetal movement of IAA througha 6-mm segment taken 7 mm behind the apex of the root were similarto those previously reported for the acropetal movement througha 12-mm segment excised 1 mm behind the apex. The smaller amountsof IAA which move acropetally through longer root segments aretherefore attributable to a limitation of the flux in the mostbasal regions of the segment. |
