The Effect of Gibberellin on Tryptophan Conversion and Elongation of the Avena Coleoptile

Gibberellic acid (GA3) enhanced directly the release of 14CO2 from tryptophan‐1‐l4C by cell free preparations of Avena coleoptile tips. The rate of tryptophan metabolism in the presence of GA3 was increased by approximately 100 per cent. The addition of auxin synthesis inhibitors to incubation flasks nullified the enhancement effect of GA3 on elongation of the coleoptile tips. These studies implicate tryptamine as an intermediate in the formation of auxin from tryptophan. The possibility of GA3‐IAA interaction in the elongation processes was also investigated. Combination treatments of these growth‐promoting substances did not induce a synergistic growth response by the coleoptile tissue.