atmdr1 and atpgp1 affect root elongation and lateral-root formation. Seedlings were grown vertically on germination plates for 3 d under white light and then transferred to new unsupplemented plates or plates supplemented with various hormones. A to C, Relative root elongation of wild type (Col), atmdr1-100, atpgp1-100, and atmdr1-100/atpgp1-100 mutants on plates supplemented with various concentrations of 2,4-D, 1-NAA, and NPA for 4 d, respectively. The percentage of relative root elongation was calculated based on control plants grown on unsupplemented media. Bars indicate the sds from 20 to 25 seedlings. The plant genotypes for A to C are indicated in A. D, Lateral root number of wild type (Col), atmdr1-100, atpgp1-100, and atmdr1-100/atpgp1-100 mutants on medium with or without 100 nm 1-NAA, 100 nm 2,4-D, and 0.1 μm NPA. Bars indicate the sds from 20 to 25 seedlings.