DIFFERENTIAL INHIBITION OF INDOLE-3-ACETIC ACID AND TRYPTOPHAN BIOSYNTHESIS BY INDOLE ANALOGUES I. TRYPTOPHAN DEPENDENT IAA BIOSYNTHESIS

Authors: ILIC, NEBOJSA - UNIVERSITY OF MARYLAND; OSTIN, ANDERS - SEWDISH UNIV OF AG SCI; Cohen, Jerry

Submitted to: Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Studies on how plants make several plant hormones have been facilitated by the use of chemical inhibitors of the processes involved. These studies have not only been useful for understanding the biology of the hormones, but have lead to the development of numerous important agricultural chemicals. Auxins are a class of plant hormones that are involved in normal growth, development and fruit ripening, but no inhibitors if auxin production by plants have previously been found. Our studies have shown that it is likely that past difficulties in finding inhibitors have their origin in the fact that plants have more than one way to make auxin. However, one outcome of recent studies on auxin biosynthesis is that it is now possible to develop systems for the study of the inhibition of these reactions. We describe our results from the screening of a series of structural analogues to an auxin precursor for inhibition and show that several are potentially useful. These studies will be useful for biochemists interested in auxin metabolism, to scientists interested in regeneration of plants from tissue culture, to molecular biologists interested in selection for auxin mutants, to scientists interested in the design of new agrochemicals, especially those interested in compounds for the alteration of fruit ripening.

Technical Abstract: Maize liquid endosperm extracts contain the enzymes necessary for all of the steps of the plant IAA biosynthetic pathway from tryptophan, andprovides 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 beta activity. Some compounds showed strong inhibition of IAA biosynthesis while having only a slight effect on the reaction rate of tryptophan synthase beta. 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.