Fig. 1.

a–c Response of a P_HSP70A-Luc reporter gene in Chlamydomonas transformants to the addition of H₂O₂ in the light and in the dark. a A truncated version (ΔHSE) of the HSP70A promoter construct known to be inducible by H₂O₂ (Shao et al. 2007) was fused to a luciferase reporter gene that at its upstream end harbored sequences of HSP70B. Dark shaded bars represent exons, light shaded bars indicate introns. The third exon of HSP70B was fused to a Renilla luciferase reporter gene with C. reinhardtii adapted codon usage (Fuhrmann et al. 2004) (LUC), indicated by a dark grey bar. The 3′ UTR of the fusion gene is encoded by the corresponding region of RBCS2. b Induction of P_HSP70A-LUC in Chlamydomonas transformants by exogenously applied hydrogen peroxide. Light grown C. reinhardtii cells were incubated in the presence of 2 mM H₂O₂ with white light of an intensity of 70 μmol photons m⁻² s⁻¹ (open circles) or in the dark (closed circles). H₂O was added to light-incubated control cultures (open squares) and to control cultures transferred to the dark (closed squares). Samples for luciferase assays were taken at the time points indicated and processed as described in Sect. “Materials and methods”. The activity was normalized with respect to cell numbers and the induction factors were calculated by comparison with untreated cells at time point 0 h. c Dependence of the degree of induction of the P_HSP70A-LUC reporter construct in Chlamydomonas transformants in the light on the concentration of exogenous H₂O₂. Experiments were performed as described in b. Samples for luciferase assays were taken after incubation for 3 h (diamonds) and after 5 h (triangles)