The mechanisms for Cu responsiveness are conserved in higher plants. A, The moss FeSOD promoter was repressed by Cu in the transgenic tobacco plants. Top, Schematic diagram of the p558 construct. The white boxes represent GTACT sequences. Bottom, GUS activities of the transgenic tobacco plants. The bars represent the GUS activities of transgenic plants cultured in the presence of 1.0 μm CuSO4. The GUS activities of the transgenic plants cultured in the absence of CuSO4 were arbitrarily set to 1.0 (dotted line). The transgenic tobacco plants containing the CaMV 35S promoter fused to the GUS gene were used as a negative control (Nt/35S). The bars indicate ± sd. B, The Arabidopsis FeSOD gene FSD1 is regulated by Cu. Top, Schematic diagram of the construct. The site of transcription initiation is indicated (+1). Black box, 5′ Untranslated region; gray box, coding region (three amino acids). Bottom, GUS activities of transgenic Arabidopsis (At/35S and At/AtFSD1) and tobacco plants (Nt/35S and Nt/AtFSD1). The 35S-GUS construct was used as a negative control. The bars represent the GUS activities of transgenic plants cultured in the presence of 1.0 μm CuSO4. The GUS activities of the transgenic plants cultured in the absence of CuSO4 were arbitrarily set to 1.0 (dotted line). The bars indicate ± sd. C, Histochemical analysis of transgenic Arabidopsis plants carrying the AtFSD1-GUS construct cultured without or with CuSO4. Transgenic Arabidopsis seedlings precultured with 0.1 μm CuSO4 for 7 d were treated without (left; −Cu2+) or with 1.0 μm CuSO4 (right; +Cu2+) for 7 d. The arrowheads indicate the cotyledons. More than three independent transgenic lines were investigated. Scale bars, 1 mm. D, Schematic diagrams of the promoter region of Arabidopsis genes regulated by Cu. FeSOD, moss FeSOD (AB370198); FSD1, FeSOD (At4g25100); miR398a, microRNA 398a (At2g03445); miR398b, microRNA 398b (At5g14545); miR398c, microRNA 398c (At5g14565); CCH, Cu chaperone (At3g56240); COPT1, Cu transporter (At5g59030); COPT2, Cu transporter (At3g46900); ZIP2, ZRT/IRT-like protein (At5g59520). The white boxes and triangles represent GTACT sequences and GTAC sequences, respectively.