THE RELATIONSHIP OF GIBBERELLIN AND AUXIN IN PLANT GROWTH

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Abstract
No synergism was found between IAA and gibberellin in the Avenu curvature test and this bioassay thus measures changes in diffusible auxin resulting from gibberellin treatment and not a synergistic action of the gibberellin on the curvature response to auxin. Gibberellin treatment causes an increase in diffusible auxin from the stem apex of dwarf pea (Pisum sativum L. var. Little Marvel) 24 to 48 hours before the elongation response in the stem. The increase in diffusible auxin in the stem apex of Centaurea cyanus L. var. Blue Boy occurs four to six days before the bolting response to gibberellin treatment under short days. The stem tissues of both the dwarf pea and Centaurea show an elongation response to IAA when the IAA is applied in a manner simulating the stem apex. Thus the growth of the dwarf pea and the bolting of Centaurea brought about by treatment with gibberellin are dependent on an increase in diffusible auxin.