The Role of the Coleoptile Apex in Controlling Organ Elongation: II. EFFECTS OF AUXIN SUBSTITUTION AND AUXIN TRANSPORT INHIBITORS ON DECAPITATED COLEOPTILES

The most widely quoted evidence that auxin controls coleoptileelongation is that auxin applied to the cut surface of a coleoptilecan obviate the effects of decapitation. A quantitative studyof this old observation shows that exogenously applied auxinonly overcomes the effects of decapitation if supplied at unphysiologicallyhigh concentrations. Furthermore, when a ring of an auxin transportinhibitor is applied just beneath the apex of an intact coleoptile,so that auxin supplied from the apex is abolished, the growthrate of the coleoptile is not reduced significantly. These experimentssuggest that coleoptile elongation is not dependent on auxintransported from the apex. Key words: Coleoptile, auxin, transport inhibitors