Auxin-promoted Transport of Metabolites in Stems ofPhaseolus vulgarisL

Abstract

The hypothesis that indol-3yl-acetic acid (IAA) stimulates solute mobilization in stems by increasing metabolite utilization (i.e. sink strength) and/or sieve tube unloading mechanisms was investigated using seedlings of Phaseolus vulgaris L. Sink strength was assessed by obtaining estimates of rates of growth, ¹⁴C incorporation into protein, sucrose metabolism, and sucrose uptake. The data obtained suggest that, whilst enhancing assimilate mobilization, IAA had no short term effect on the sink strength of the treated stumps. In several experiments involving long distance transport of ¹⁴C-assimilates, the magnitude of auxin-promoted transport was found to be insensitive to potential changes in sink strength. Furthermore, ¹⁴C transport profiles demonstrated that the site of hormone action was not confined to its point of application.