Figure 2.

Contribution of MDR1 and MDR4 to Acropetal and Basipetal Auxin Transport in Roots.

(A) Acropetal auxin transport measured by applying ³H-IAA to the root-shoot junction zone and later determining the amount of radioactivity in an apical portion of the root. Values shown are mean ± se of five independent trials, each involving eight roots per genotype. BA, benzoic acid, a molecule not acted on by the polar transport stream that was used as a control.

(B) Auxin transport assayed by induction of ProDR5:GUS. Acropetal: auxin applied at the junction zone activated GUS expression and quantified by MUG assay in more apical regions of the root. Baseline GUS activity was 860 ± 150 relative fluorescence units h⁻¹ in the wild type and 590 ± 95 relative fluorescence units h⁻¹ in mdr1. Basipetal: auxin applied at the root tip induced GUS expression in more basal portions of the root. Values are mean fold induction over mock treatment ± se, and n = 6 trials of 10 roots per genotype.

(C) Dose–response curve for ProDR5:GUS induction shows that roots of mdr1 and the wild type were similarly sensitive to auxin; mean ± se, n = 6 trials for each point, with 10 roots per measurement.

(D) Basipetal auxin transport measured by applying ³H-IAA to the root apex and later determining the amount of radioactivity in a basal segment of the root. Values shown are mean ± se of seven independent trials, each involving eight roots per genotype.