ISOLATION AND CHARACTERIZATION OF MUTANTS OF ARABIDOPSIS-THALIANA WITH INCREASED RESISTANCE TO GROWTH-INHIBITION BY INDOLEACETIC ACID-AMINOACID CONJUGATES

Two mutants of Arabidopsis thaliana that are resistant to growth inhib ition by indole-3-acetic acid (IAA)-phenylalanine have been isolated. Both mutants were 2- to 3-fold more resistant than wild type to inhibi tion by IAA-phenylalanine, IAA-alanine, and IAA-glycine in root growth assays. The mutant icr1 (but not icr2) also shows some resistance to IAA-aspartate. Studies using H-3-labeled IAA-phenylalanine showed that the uptake of conjugate from the medium by icr1 was the same as wild type and was reduced by about 25% in icr2. No differences in hydrolysi s of the exogenous conjugate were detected between the mutants and the ir wild-type parents. There was no significant metabolism of the IAA r eleased from the [H-3]IAA-phenylalanine, whereas exogenous [H-3]IAA wa s rapidly metabolized to two unidentified products considerably more p olar than IAA. Analysis of a cross between icr1 and icr2 indicated tha t these mutations were at distinct loci and that their effects were ad ditive, and preliminary mapping data indicated that icr1 and icr2 were located at the top and bottom of chromosome V, respectively.