lsolation and Characterization of Mutants of Arabidopsis thaliana with lncreased Resistance to Crowth lnhibition by lndoleacetic Acid-Amino Acid Conjugates'

Two mutants of Arabidopsis thaliana that are resistant to growth inhibition by indole-3-acetic acid (IAA)-phenylalanine have been isolated. Both mutants were 2to 3-fold more resistant than wild type to inhibition by IAA-phenylalanine, IAA-alanine, and IAAglycine in root growth assays. l h e mutant icrl (but not icr2) also shows some resistance to IAA-aspartate. Studies using 3H-labeled IAA-phenylalanine showed that the uptake of conjugate from the medium by icrl was the same as wild type and was reduced by about 25% in icr2. No differences in hydrolysis of the exogenous conjugate were detected between the mutants and their wild-type parents. There was no significant metabolism of the IAA released from the [3HlIAA-phenylalanine, whereas exogenous [3H]IAA was rapidly metabolized to two unidentified products considerably more polar than IAA. Analysis of a cross between icrl and icr2 indicated that these mutations were at distinct loci and that their effects were additive, and preliminary mapping data indicated that icrl and icr2 were located at the top and bottom of chromosome V, respectivel y.