Figure 6.

Reducing compounds affect cadmium-dependent induction of the pSULTR1;2∷LUC reporter.

(a) Addition of 1 mm cysteine or γ-EC to the growth media lowers the response of the control pSULTR1;2∷LUC line to cadmium over a 12-h time course.

(b) Cadmium-dependent induction of the luciferase reporter gene is affected by reducing compounds. Exposure to 100 μm CdCl₂ induces the transcription of the pSULTR1;2∷LUC reporter gene (Cd). The addition of the reducing compounds cysteine (Cd + 1 mm Cys) or glutathione (Cd + 1 mm GSH) to the growth media strongly represses the cadmium-induced luciferase activity. The non-physiological reducing agents DTT (Cd + 1 mm DTT) and BHA (Cd + 200 μm BHA) also repressed the induction of the reporter gene, suggesting that changes in the cellular redox state is a factor controlling the expression of the SULTR1;2 gene. All images were quantified after 6 h of exposure to the specified compound.

(c) Schematic representation of putative signals involved in the regulation of the high-affinity sulfate transporter, SULTR1;2, during cadmium stress. Glutathione and cysteine are known to repress SULTR1;2 under many conditions, including sulfur starvation and cadmium stress. Characterization of the nrc1 and nrc2 mutants suggests, however, that both GSH demand and changes in cellular redox are required for Cd-dependent transcriptional changes.