Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/1998
Publication Date: N/A
Interpretive Summary: Auxins are a class of plant hormones that are involved in normal growth, development and fruit ripening, and have been studied for more than 120 years. However, it remains unclear how plants make this important natural growth regulator. Early studies suggested that auxin was made from the amino acid tryptophan, however plants that do not make tryptophan can make auxin. We describe a cell free system obtained from corn seedlings that is able to make the major auxin of plants from an early precursor without first making tryptophan. This is the first demonstration of cell-free tryptophan-independent auxin biosynthesis. These studies will be useful for biochemists interested in understanding and regulating auxin metabolism, and to scientists interested in modification of fruit ripening, rooting characteristics, and other developmental changes and to educators interested in describing progress in a long studied field of research.
Technical Abstract: The enzymatic synthesis of indole-3-acetic acid from indole by an in vitro preparation from maize, that does not use tryptophan as an intermediate, is described. Light grown seedlings of normal and orange pericarp mutant maize were shown to contain the necessary enzymes to convert C indole to IAA. The reaction was not inhibited by unlabeled tryptophan and neither C tryptophan nor C serine substituted for C indole in this in vitro system. The reaction had a pH optimum above 8.0, required a reducing environment and an oxidation potential near that of ascorbate. The results obtained with this in vitro enzyme preparation provide strong additional evidence for the presence of a tryptophan-independent IAA biosynthesis pathway in plants.