Tryptophan as an auxin precursor in cucumber seedlings

The conversion of tryptophan-14C to indoleacetic acid-14C in cucumber hypocotyls occurred under both sterile and non-sterile conditions. This conversion was not reduced under sterile conditions. The growth response of cucumber hypocotyl segments to exogenously supplied tryptophan was almost as great under sterile conditions as when contaminating microorganisms were present. These data are consistent with the hypothesis that tryptophan is a normal precursor of indoleacetic acid in cucumber tissues. The conversions of tryptamine-14C and indoleethanol-14C to indoleacetic acid-14C also occurred under both sterile and non-sterile conditions. Indoleethanol-14C was formed from tryptamine-14C. Hypocotyl segment growth responses to tryptamine and to indoleethanol were not decreased under sterile conditions.