Abstract
3H-serine+14C-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 3H/14C ratios were determined. The 3H/14C ratio of IAA was lower than the 3H/14C ratio of Try. However, the same decrease of the IAA 3H/14C ratio was found when 3H, 14C-Try was supplied instead of 3H-serine+14C-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.