Incorporation of Deuterium into Indole-3-acetic Acid and Tryptophan in Zea mays Seedlings Grown on 30 % Deuterium Oxide

The onset of de novo synthesis of IAA and tryptophan in seedlings of Zea mays sweet corn, var. Silver Queen was examined. Deuterium labeled water was used as a general precursor to minimize assumptions as to the biosynthetic route. Protium in positions 2, 4, 5, 6, & 7 of the indole ring are non-exchangeable (Magnus et al., 1980). IAA and tryptophan synthesized via the shikimic acid pathway would contain deuterium in one or more of these positions. Protium on the indene nitrogen, the carboxyl, the amino group (tryptophan only), or the protium alpha to the carboxyl (IAA only), exchange readily and were removed by base catalyzed exchange prior to GGMS analysis. We have demonstrated, by means of gas chromatography-selected ion monitoring mass spectrometry, that 7 d old, etiolated seedlings grown on 30 % D2O incorporate deuterium into tryptophan, but not into IAA. Randomization of deuterium in the indole ring during mass spectrometry makes it difficult to localize the deuterium to the tryptophan ring. Deuterium NMR was used for the determination of the position of deuterium incorporated into tryptophan. NMR data are presented showing deuterium incorporation into the 6 position of the tryptophan indole ring.