INDOLEACETIC-ACID SYNTHESIS IN SOYBEAN COTYLEDON CALLUS-TISSUE

Growth of an auxin-requiring soybean cotyledon callus tissue (Glycine max L., Merr. cv. ''Acme'') was promoted by tryptophan, tryptamine, indole, indoleacetamide and, to a very slight degree, anthranilic acid. When tryptophan-3-14C was supplied in the growth medium, labeled IAA was found in both the tissue and the medium. Medium from which the cells had been removed also converted labeled tryptophan to IAA. Soybean callus contained 0.044 .mu.mol/g free tryptophan, but this is apparently not available for conversion to IAA. While exogenously supplied tryptophan could elevate a specific internal pool where IAA synthesis occurs some of the growth on a tryptophan medium can be accounted for by external conversion.