Indole-3-Acetic Acid Biosynthesis in the Mutant Maize orange pericarp, a Tryptophan Auxotroph

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.     

Major international AIDS research collaborations

Science lists the major collaborative research projects throughout sub-Saharan Africa. This list will be updated periodically at www.sciencemag.org/feature/data/africacollaborations.shl. Please send additions and changes to science_news@aaas.org.     

Confronting conference complexities

Next month, Hoosen "Jerry" Coovadia will chair the XIII International AIDS Conference here, the first time this high-profile gathering has been held in a developing country. Coovadia and the other organizers have gone to great lengths to make the conference work smoothly. Photos by Malcolm Linton