An in vitro system from maize seedlings for tryptophan-independent indole-3-acetic acid biosynthesis

The enzymatic synthesis of indole-3-acetic acid (IAA) from indole by an in vitro preparation from maize (Zea mays L.) that does not use tryptophan (Tr p) as an intermediate is described. Light-grown seedlings of normal maize a nd the maize mutant orange pericarp were shown to contain the necessary enz ymes to convert [C-14]indole to IAA. The reaction was not inhibited by unla beled Trp and neither [C-14]Trp nor [C-14]serine substituted for [C-14]indo le in this in vitro system. The reaction had a pH optimum greater than 8.0, required a reducing environment, and had an oxidation potential near that of ascorbate. The results obtained with this in vitro enzyme preparation pr ovide strong, additional evidence for the presence of a Trp-independent IAA biosynthesis pathway in plants.