Metabolism ofAuxininTomatoFruit Tissue Formation ofHighMolecular Weight Conjugates ofOxindole-3-Acetic

Highperformance liquid chromatography ofextracts oftomato (Lycopersicon esculentum Mill.) incubated witharelatively low concentration (4jAm) of[1-14C]indole-3-acetic acid(IAA) revealed thepresence oftwomajor polar metabolites. Hydrolysis ofthetwo metabolites with7NNaOHyielded thesamecompound, which hadaretention timesimilar tothat ofring-expanded oxindole-3acetic acid(OxIAA) onhighperformance liquid chromatography. Theidentity oftheindolic moiety ofthese conjugates asOxIAA wasfurther confirmed bygaschromatography-mass spectrometry. Chromatography ofthetwoOxIAAconjugates onacalibrated BioGelP-2column indicated that their molecular weights areabout 1200and1000. Aspartic acidandglutamic acidwerethemajor aminoacids detected inacidhydrolysates ofthetwoconjugates. Increasing theconcentration ofIAAintheincubation medium resulted inanincrease intheformation ofindole-3-acetylaspartic acid(lAAsp) withaconcomitant decrease intheformation ofthe twoOxIAAconjugates. Feeding experiments withlabeled lAAsp andOxIAAshowed that lAAsp andnotOxIAAistheprecursor of these conjugates. Thedataobtained indicate that exogenous IAA isconverted intomatopericarp tissue tohighmolecular weight conjugates, presumably peptides, ofOxIAAviatheoxidation of lAAsp. Theoxidation ofIAAsp seemstobearate-limiting step in theformation ofthese conjugates fromexogenous IAA.