Abstract: | Phaseolus multiflorus plants at three stages of developmentwere decapitated either immediately below the apical bud orlower down at a point 1 cm above the insertion of the primaryleaves. Growth regulators in lanolin were applied to the cutstem surface. IAA always inhibited axillary bud elongation anddry-matter accumulation, and enhanced internode dry weight butnot elongation. GA3 applied below the apical bud greatly increasedinternode elongation and dry weight, but simultaneously reducedbud elongation and dry-weight increase. Application of GA3 1cm above the buds had no effect on bud elongation in the youngestplants, but enhanced their elongation in the two older groups.IAA always antagonized GA3-enhancement of internode extensiongrowth, whereas its effects on GA3-enhanced dry-matter accumulationdepended on the stage of internode development. Bud elongationwas greater in plants treated with GA3+IAA than in plants treatedonly with IAA, except in the youngest plants decapitated immediatelybelow the apical bud, where GA3 caused a slight increase inIAA-induced bud inhibition. GA3 increased inhibition of buddry weight by IAA in the two youngest groups of plants, butslightly reduced it in the oldest plants. No simple compensatorygrowth relationship existed between internode and buds. It wasconcluded that, (1) auxin appears to be the principal growthhormone concerned in correlative inhibition, and (2) availabilityof gibberellin to internode and buds is of importance as a modifyingfactor in auxin-regulated apical dominance by virtue of itslocal effects on growth in the internode and in the buds. |