Hypocotyl lengths of ethylene mutants treated with phenanthrene. Hypocotyl length of 4 d old Arabidopsis seedlings grown in absence or presence of phenanthrene in the dark. Top: Mean root lengths with standard error bars. Bottom: Response (%) is the ratio of root length on phenanthrene to root length without phenanthrene treatment. Bars represent mean ± error (see Methods section for calculation). Horizontal, dashed lines mark the error range for Columbia WT. At least ten seedlings were measured for each treatment and genotype.