Clarke type electrode

The activity of the STN7 kinase is known to be activated by a reduced PQ pool (Bellafiore et al., 2005) . Its activity can be visualized by following the corresponding change in the phosphorylation state of the light-harvesting complex of PSII (LHCII). We isolated thylakoid membranes from Arabidopsis plant material grown as for the array analyses and tested the LHCII phosphorylation state by western immunoblotting using an anti-phosphothreonine antiserum following standard procedures for plants grown in PSI or PSII light (Dietzel et al., 2011) .
For respiration measurements, Col 0 and stn7 mutant seedlings were grown according to the micro-array conditions on soil. After 10 days in continuous white light, plants were transferred to PSI light either for 6 days (PSI-plants) or for 3 days followed by a 3-day shift to PSII light (PSIII-plants) before the plant material was harvested. O 2 generation and consumption was measured using a Clarke-type electrode (Hansatech, Kings Lynn, UK) filled with 10 mM sodium phosphate buffer (pH 7.2), 10 mM KCl, and 10 mM glucose. Illumination was provided by a halogen lamp with an intensity of 750 mE m À2 s À1 . Plantlets were cut into small pieces to enable homogeneous oxygen exchange in the electrode.

A 10 ml volume of bacteria grown until 0.6 OD 600 were stressed with 130 g/ml TiO 2 , 170g/ml ZnO, 0.3mM ZnSO 4 or 5mM H 2 O 2 for one hour under shaking at 37°C. Bacteria were then pelleted by centrifugation at 6,000 rpm for 10 min. The pellets were washed with 1 ml of PBS and centrifuged (13,000 rpm, 5 min). The pellets were finally resuspended in 8 ml of PBS. The catalase activities were immediately determined on cells using a Clarke-type electrode (Hansatech, Kings Lynn, UK), as described by Rorth and Jensen [41] . The specific activities were calculated as the number of generated O 2 moles/min/CFU.