Tryptophan-dependent indoleacetic-acid biosynthesis from indole, demonstrated by double-labelling experiments.

(3)H-serine+(14)C-indole were administered to tips of sterily-grown pea seedlings and of non-sterile oat coleoptiles. The Try and IAA produced were extracted and purified by paper chromatography, and their (3)H/(14)C ratios were determined. The (3)H/(14)C ratio of IAA was lower than the (3)H/(14)C ratio of Try. However, the same decrease of the IAA (3)H/(14)C ratio was found when (3)H, (14)C-Try was supplied instead of (3)H-serine+(14)C-indole. This result supports the view that Try is the native IAA precursor and that no significant bypass from indole to IAA exists in the plant material used.