Effect of relative hormone concentration on auxin-gibberellin interaction in correlative inhibition of axillary buds.

Indole-3-acetic acid (IAA) applied to the fully elongated second internode of decapitated Phaseolus multiflorus plants always inhibited axillary bud elongation at concentrations down to 100 μg/g lanolin, whereas gibberellic acid (GA3) enhanced bud elongation at concentrations down to 1000 μg/g lanolin. Lower concentrations than these of either IAA or GA3 were without significant effect. All possible combinations of IAA and GA3 within the concentration range 10(1) to 10(5) μg/g lanolin were antagonistic; IAA tending to inhibit, and GA3 promote, axillary bud elongation growth. Treatment of an elongating internode with the hormones resulted in an increase in inhibition of bud growth by IAA in the presence of GA3.