Figure 1.—

ibr1 and ibr10 mutants display IBA- and 2,4-DB-resistant root elongation. (A) ibr mutant root elongation on IBA and IAA. Col-0 (Wt), ibr10-1, and six ibr1 alleles were plated on medium containing 0.5% sucrose with no hormone, 15 μm IBA or 120 nm IAA. Root length was measured after 7 days. Error bars show standard errors of mean root lengths (n ≥ 13). (B) ibr mutant root elongation in response to increasing IBA concentrations. Seeds were stratified for 3 days at 4° in 0.1% agar prior to incubation under white light for 2 days at 22°. Germinating seeds were transferred to medium containing 0.5% sucrose (no hormone) or supplemented with the indicated concentration of IBA. Roots were measured after 8 additional days of growth under yellow-filtered light. Error bars show standard errors of mean root lengths (n ≥ 10). ibr3-1 (Zolman et al. 2007) is included for comparison with ibr10 and ibr1. chy1-3 (Zolman et al. 2001a) is included as an IBA-resistant control. (C) ibr mutant root elongation on synthetic auxins. Roots were measured as in B. Error bars show the standard errors of mean root lengths (n ≥ 12). chy1-3 is included as a 2,4-DB-resistant control. (D) The ibr1 ibr3 ibr10 triple mutant remains more IBA responsive than the ibr3 chy1 double mutant. Root elongation was evaluated as in B. Error bars show standard errors of mean root lengths (n ≥ 8).