Photosynthetic oxygen measurements
For rescue experiments cells were pre-treated for 1 week with 20 μM AA, 20 μM SA, 300 nM GSH, 100 μM Fe and 300 nM Zn followed by a 21 days incubation in 600 nM Cd and 10 μM Cr. Additionally cell cultures treated only with 5 μM Pb for 21 days were measured. Roughly 2000 cells were used for each run with 3–4 light/dark cycles, which were repeated 3 times each. Oxygen turnover as indicator for photosynthetic activity was measured by a Hansatech (King’ Lynn, UK) polarographic oxygen electrode and μM oxygen/h/mg chlorophyll were determined. Illumination was set to 200 μM photons m2 s−1 to enable comparison with in earlier experiments