Transport of indoleacetic acid (IAA) and its conjugates in nodal stem segments of Phaseolus vulgaris L

Donor agar blocks containing either [2-acetyl-14C] IAA; [2-acetyl-14C] indole-3-acetyl-L-aspartate; [2-aceyl-14] indole-3-acetyl-L-glycine; or [2-acetyl-14C] indole-3-acetyl-L-alanine were placed on either the apical or the basal cut surface of stem segments each bearing an axillary bud in the middle. A receiver block was placed on the end opposite to the donor. After transport, the segments were divided into five equal sections plus the bud, and the radioactivity of donors, receivers and each part of the stem segments was counted. For all substances, the amount of 14C transported to the bud from the base was the same or greater than that from the apical end. After basipetal transport, the distribution of 14C in the segment declined sharply from apex to base. The opposite was true for acropetal transport. Transport for the three IAA conjugates did not different substantially from each other. The IAA transport inhibitor, naphthylphthalamic acid (NPA), inhibited basipetal 14C-IAA transport to the base of the stem segment but did not alter substantially the amount of 14C-IAA recovered from the bud. The results will be discussed in relation to axillary bud growth regulation