Figure 2.

Deletion analysis of P-PvSR. Schematic diagrams of the constructs used for transient expression assays are shown at left. The black areas indicate the MRE-like sequence (−212/−206), while the crosshatched area indicates a mutated MRE-like sequence. The numbers on the far left indicate the 5′ end points of the promoter fragments relative to the transcription start site. In each experiment, protoplasts were transformed with each of the plasmids shown and a CaMV 35S:Luc construct, pBI221-Luc, was incubated for 24 h in heavy metal-free MS medium either with (+) or without (−) 15 μm HgCl₂. The plasmid containing a promoter-less GUS (pBI101) was used as a negative control, while the CaMV 35S:GUS-containing plasmid (pBI221) was used as a positive control. Activity, given as relative GUS/LUC units (fold), is averaged from three independent experiments. sd is indicated. The ratio of the promoter activity with HgCl₂ stress compared to the promoter activity without HgCl₂ stress (induction ratio) is shown at the far right. Significant difference between −Hg and +Hg conditions was analyzed using one-sided paired t test (P < 0.01 [**]). Numbers above the bar of pBmMRP0.2 sample indicate the percentage of heavy metal-inducible GUS activity relative to that of pBMRP0.2 sample, and its significant difference test was assessed by one-sided paired t test (P < 0.05 [*]). No statistical differences of GUS activity existed between these two samples in absence of heavy metal (P > 0.05; Student's t test). n.d., Not detectable.