Abstract
We tried to perform the chemical genetics screening by Brz (brassinazole) that was synthesized as the first specific inhibitor of brassinosteroid biosynthesis. Target of Brz220 is the cytochrome P450 enzyme encoded by DWF4. In order to analyze in detail the mechanisms of brassinosteroid signal transduction, we screened for mutants that showed longer hypocotyls than wild type when grown with Brz220 in the dark, and designated bil mutants (Brz-insensitive-long hypocotyl). We identified a semidominant mutant, bil5, from fast neutron-treated lines. Hypocotyl elongation of these plants on Brz medium was at least twice that of the wild type. Adult bil5 plants showed pale green and thin leaves, and thin and shortened inflorescences. Furthermore, By microscope observation, the palisade cell and spongy cell of bil5 mesophyll tissues were smaller and disturbed in comparison with wild type. Number and size of secondary xylem cell of bil5 inflorescences were decreased.
