Isoxaben-resistant mutants are sensitive to C17. A to E, Root growth of 5-d-old wild type (Col-0), a C17-tolerant mutant (8P), and three isoxaben-tolerant mutants (ixr1-1, ixr1-2, and ixr2-1) grown in the absence (A) or presence of 4 nm isoxaben (B), 200 nm C17 (C), 500 nm C17 (D), and 1 µm C17 (E). Scale bars, 5 mm.