Movement and distribution of 14C-indole-3-acetic acid in branches and rooted cuttings of Douglas-fir

The transport of ¹⁴C-indole-3-acetic acid in branch terminals and stems of rooted cuttings of Pseudotsuga menziesii (Mirb.) Franco was studied to determine if the plagiotropic growth of cuttings might result from an accumulation of basipetally transported auxin in the morphologically upper side of cuttings stems. Twenty-four h after application of 10 μl of ¹⁴C-IAA solution to the cut surface of decapitated, rooted cuttings, nearly twice as much activity was detected in extracts of tissue from the morphologically upper than from the lower halves of the stems. A similar distribution of activity was observed in horizontal branch terminals and in branch terminals which had been tied vertically for 2 weeks. The magnitude of the difference in activity between the 2 sides of the stem was greater in the horizontal than in the vertical branches.
There was no significant difference in transport through the upper and lower sides of excised stem segments from cuttings or branch terminals. In segments from rooted cutting stems, however, significantly more radioactivity from ¹⁴C-IAA donor blocks was detected in the lower than in the upper halves of segments.