The O–I STI571 solubility dmso 1 curves measured

with the five different colors were fitted together with the restriction of common values of J and Tau(reox), as these parameters are unlikely to depend on the color of light. Calculation of Sigma(II)λ by the multi-color-PAM-software is based on the fitted value of the time constant Tau and the value of incident PAR, using the following general equation: $$ \textSigma(\textII)_\lambda = \frack(\textII)L \cdot \textPAR = \frac1\tau \cdot L \cdot \textPAR, $$ (1)where k(II) is the rate constant of PS II turnover and Tau the time constant of QA-reduction during the O–I 1 rise, L is Avogadro’s constant, PAR is the photon fluence rate of the light driving the O–I 1 rise and Sigma(II)λ the wavelength- and sample-dependent absorption cross section of PS II (for further explanations, see “Results and interpretation” section). Measurement of absorptance Sample absorptance was measured using the same Optical Unit ED-101US/MD as for fluorescence GSI-IX measurements (see Fig. 1), but with the detector-unit

MCP-D being moved from the 90° position (relative to the emitter-unit) to the 180° position. The long-pass filter in front of the detector was exchanged against suitable neutral buy BKM120 density filters and pin-hole diaphragms, so that pulse-modulated transmittance signals could be measured both with the suspension medium as such, I medium, and with the suspension medium containing Chlorella or Synechocystis, I sample. The absorptance a (=1 − transmittance) was calculated as a = 1 – I sample/I medium. With the given optical geometry almost all light entering the 10 × 10 mm cuvette via the emitter-perspex-rod is picked up by the detector-perspex-rod,

unless absorbed by the sample. Photosynthetic cAMP organisms and sample preparation Experiments were carried out with dilute suspensions of green unicellular algae Chlorella vulgaris and cyanobacteria Synechocystis PCC 6803. Chlorella was cultured in natural day light (north window) at 20–40 μmol/(m2 s) and room temperature (25 °C) in an inorganic medium (Pirson and Ruppel 1962) under ambient air. Synechocystis was grown photoautotrophically in artificial light (tungsten) at 30  μmol/(m2 s) and 30 °C in Allen’s (1968) medium under ambient air. Both cultures were shaken manually at least four times per day. Cultures were frequently diluted so that chlorophyll content did not exceed 5–10 mg/L. Experiments were carried out at room temperature with diluted suspensions at 200–300 μg/L, as determined with a calibrated WATER-PAM chlorophyll fluorometer (Walz). For sample preparation the cuvette was first filled with 1.4 mL of culture medium and then stock suspension was added dropwise to the stirred sample until signals corresponding to 200–300 μg/L were reached.