Adventitious Root Formation in Bean Hypocotyl Cuttings in Relation to IAA Translocation and Hypocotyl Anatomy

Adventitious roots develop in bean hypocotyl cuttings in four rows parallel to and between the four pairs of vascular bundles, in contrast to their irregular development in petiole and epicotyl cuttings where the distribution pattern of xylem bundles is also irregular. Auxin, applied acropetally or basipetally, increases the number of roots but does not alter the pattern of their emergence. Similarly, [2-14C]IAA which is translocated mainly via the vascular bundles (but also laterally towards the cortex and pith) accumulates in the root-forming areas irrespective of how it was applied. Consequently, it is deduced that the adventitious root development in bean hypocotyls is induced by IAA accumulation, but that IAA does not affect or modify the predetermination of rooting sites.