J. Normanly "Auxin Metabolism" Physiologia Plantarum (1997) Vol 100:431-442
N. Ilic, J. Normanly, and J. D. Cohen "Quantification of free plus conjugated indole-3-acetic acid in Arabidopsis requires correction for the non-enzymatic conversion of indolic nitriles" Plant Phys. (1996) Vol 111:781-788
J. Normanly, J. P. Slovin, and J. D. Cohen "Update on hormones: Rethinking auxin biosynthesis and metabolism" Plant Phys.,107:323-329 (1995)
This review focuses on the new and more complex picture of IAA biosynthesis that has emerged as a result of recent experiments.
J. Normanly, J. D. Cohen, and G. R. Fink "Arabidopsis thaliana auxotrophs reveal a tryptophan-independent biosynthetic pathway for indole-3-acetic acid" Proc. Natl. Acad. Sci., 90:10355-10359 (1993)
We used tryptophan auxotrophs of the dicot > Arabidopsis thaliana (wall cress) to determine whether tryptophan has the capacity to serve as a precursor to the auxin, indole-3-acetic acid (IAA). Quantitative gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) revealed that the trp2-1 mutant, which is defective in the conversion of indole to tryptophan, accumulated amide- and ester-linked IAA at levels 38-fold and 19-fold, respectively, above those of wild type. Tryptophan and free IAA were isolated from the trp2-1 mutant grown in the presence of [15N]anthranilate and [2H5]tryptophan, and the relative 15N and 2H5 enrichments of tryptophan and IAA were determined via GC-SIM-MS. The 15N enrichment of tryptophan, 13%+/- 4%, was less than the 15N enrichment of the IAA pool, 39% +/- 4%; therefore, IAA biosynthesis occurs via a tryptophan-independent pathway. The amount of 2H5 incorporated by the plant into IAA from tryptophan (95+/- 4%) was low and only slightly above the level of spontaneous, nonenzymatic conversion of [2H5]tryptophan to [2H5]IAA. These results show that the dicot > Arabidopsis is similar to the monocot Zea mays in that the major route of IAA biosynthesis does not occur through tryptophan.