Maize liquid endosperm extracts contain the enzymes necessary for all of the steps of the plant IAA biosynthetic pathway from tryptophan, and provide a means to assay the pathway in vitro. We have analyzed the reactions in the presence of a series of indole and indole-like analogues in order to evaluate the potential of these compounds to act as inhibitors of IAA biosynthesis. Such inhibitors will be useful to investigate the tryptophan to IAA pathway, to determine the precursors and intermediates involved, and to select for mutants in this process. A number of such compounds were tested using in vitro enzyme assays for both the tryptophan dependent IAA biosynthesis pathway and for tryptophan synthase β activity. Some compounds showed strong inhibition of IAA biosynthesis while having only a slight effect on the reaction rate of tryptophan synthase β. These results: (1) show that IAA biosynthesis can be selectively inhibited relative to tryptophan biosynthesis; (2) suggest potential ways to screen for IAA biosynthetic pathway mutations in plants; and (3) provide additional tools for studies of IAA biosynthesis in plants.
Bibliographical noteFunding Information:
These studies were supported by U.S. Department of Energy grant DE-AI02-94ER20153 and by the Swedish Council for Forestry and Agricultural Research (SJFR). We thank Drs. Janet P. Slovin and Volker Magnus for their comments on the manuscript and Drs. Todd J. Cooke and Göran Sandberg for their help with personnel exchange.
- Auxin biosynthesis
- Auxin inhibitors
- Indole analogues
- Zea mays