The maize mutant orange pericarp is a tryptophan auxotroph, which results from mutation of two unlinked loci of tryptophan synthase B. This mutant was used to test the hypothesis that tryptophan is the precursor to the plant hormone indole-3-acetic acid (IAA). Total IAA in aseptically grown mutant seedlings was 50 times greater than in normal seedlings. In mutant seedlings grown on media containing stable isotopelabeled precursors, IAA was more enriched than was tryptophan. No incorporation of label into IAA from tryptophan could be detected. These results establish that IAA can be produced de novo without tryptophan as an intermediate.

orange pericarp (orp) is a seedling lethal mutant of maize caused by mutations in the duplicate unlinked recessive loci orp1 and orp2. Mutant seedlings accumulate two tryptophan precursors, anthranilate and indole, suggesting a block in tryptophan biosynthesis. Results from feeding studies and enzyme assays indicate that the orp mutant is defective in tryptophan synthase beta activity. Thus, orp is one of only a few amino acid auxotrophic mutants to be characterized in plants. Two genes encoding tryptophan synthase beta were isolated from maize and sequenced. Both genes encode polypeptides with high homology to tryptophan synthase beta enzymes from other organisms. The cloned genes were mapped by restriction fragment length polymorphism analysis to approximately the same chromosomal locations as the genetically mapped factors orp1 and orp2. RNA analysis indicates that both genes are expressed in all tissues examined from normal plants. Together, the biochemical, genetic, and molecular data verify the identity of orp1 and orp2 as duplicate structural genes for the beta subunit of tryptophan synthase.

orange pericarp (ofp) is a seedling lethal mutant of maize caused by mutations in the duplicate unlinked recessive loci O r p l and orp2. Mutant seedlings accumulate two tryptophan precursors, anthranilate and indole, suggesting a block in tryptophan biosynthesis. Results from feeding studies and enzyme assays indicate that the ofp mutant is defective in tryptophan synthase p activity. Thus, orp is one of only a few amino acid auxotrophic mutants to be characterized in plants. Two genes encoding tryptophan synthase p were isolated from maize and sequenced. Both genes encode polypeptides with high homology to tryptophan synthase p enzymes from other organisms. The cloned genes were mapped by restriction fragment length polymorphism analysis to approximately the same chromosomal locations as the genetically mapped factors orpl and orp2. RNA analysis indicates that both genes are expressed in all tissues examined from normal plants. Together, the biochemical, genetic, and molecular data verify the identity of orpl and orp2 as duplicate structural genes for the p subunit of tryptophan synthase.

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Methionine is an essential amino acid critical to human, livestock, and poultry nutrition. A microbiological method has been tested for use as a rapid, inexpensive, and reliable means of screening maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] seed for methionine concentration. Maize and soybean meal samples with various methionine contents were defatted before enzymatic proteolysis. An aliquot of each hydrolyzate was added to liquid media free of methionine, autoclaved, and inoculated with a bacteria auxotrophic for methionine. After incubation for 20 h, the turbidity of the cultures was measured and methionine concentration was calculated from standard curve data. Significant positive correlation (r = 0.74 maize; r = 0.88 soybean) was found between the microbiological and chemical determinations. These results demonstrate that the less expensive microbiological procedure would have great utility in a methionine enhancement plant breeding program.

5-Hydroxy-3,5-di-tert-butyl-2-furanone (4). White crystals of 4 were prepared by the method of Nishinaga:3* NMR <51.03 (s, 9 H, 5-t-Bu), 1.25 (s, 9 H, 3-t-Bu), 2.84 (1 , OH), 6.78 (s, 1 H, olefinic).4.5-Epoxy-6-oxo-2,4-di-iert-butylcyclohex-2-enone (7). The method of Grierer and Imsgard8 was used to produce yellow-orange needles of 7 after recrystallization from petroleum ether: NMR S 1.09 (s, 9 H, 4-t-Bu), 1.20 (s, 9 H, 2-t-Bu), 3.83 (s, 1 ), 7.09 (s, 1 H, olefinic).3.5-Di-tert-butyl-l-oxacyclohepta-3,5-diene-2,7-dione (9). The method described by Demmin and Rogic11 2was used to prepare 9. Recrystallization from n-pentane yielded colorless cubes. 9: NMR 1.13 (s, 9 ), 1.24 (s, 9 ), 6.