Ethylene reporter gene expression in plants treated with phenanthrene and ACC, and grown in the dark. Histochemical staining of GUS activity in CH5B::GUS (A-D) and AtGSTF2::GUS (E-H) transgenic Arabidopsis plants grown for 4 d in the dark. A and E, 0 mM phenanthrene, 0 μM ACC; B and F, 0 mM phenanthrene, 20 μM ACC; C and G, 0.25 mM phenanthrene and 0 μM ACC; D and H, 0.25 mM phenanthrene, 20 μM ACC. Seedlings were stained for 15 h for GUS activity in staining buffer containing 2 mM 5-bromo-4-chloro-3-indolyl-b-D-glucuronide. Scale bars 1 mm.