This hypothesis is supported by action spectra of photodamage to PS II with peaks in the UV-A and blue region, resembling those of model manganese compounds and differing considerably from check details PS II absorption spectra (Hakala et al. 2005). Whereas measurements of the wavelength dependence of photoinhibition in leaves are complicated by intra-leaf light gradients and fluorescence reabsorption, it can be investigated in a straight forward way in optically thin suspensions. As this topic is close to the heart of Osmond (1981, 1994) to whom this contribution is dedicated, in addition to the technical and methodological aspects of

the multi-color-PAM also an application of this this website new device in the study of the wavelength dependence of photoinhibition will be presented. In this application, use of the possibility is made to adjust defined rates of quanta absorption by PS II with blue and red lights in a dilute suspension of Chlorella. If photoinhibition were just an unavoidable consequence of PS II turnover, equal turnover rates should induce equal loss

in PS II quantum yield. It will be shown that the damaging effect is distinctly larger with blue light. Materials and methods Experimental setup The experiments were carried out with a first prototype of a multi-color-PAM chlorophyll fluorometer developed by the authors, which recently has become commercially available (Heinz Walz GmbH, Germany). This device is based on a chip on board (COB) light-emitting diode (LED) array consisting of 60 Power-LED chips mounted on a 10 × 10 mm area, featuring a total of eight different colors, which serve for pulse-modulated ML, AL, FR light, ST pulses, and MT pulses, equivalent

to SP. Figure 1 shows a block diagram of the experimental setup. The emitter–detector units are mounted on an Optical Unit with four light-ports (ED-101US/MD), essentially Tryptophan synthase identical to the one introduced for the XE-PAM and phyto-PAM chlorophyll fluorometers (Kolbowski and Schreiber 1995; Schreiber et al. 1993). Fig. 1 Block diagram of the multi-color-PAM set-up for measurements with suspensions using the optical unit ED-101US/MD (see text for explanations) Light emission by the multi-color LED array (1) is controlled by separate LED drivers for the various light qualities, which are triggered with 2.5-μs time resolution under firmware/software Nirogacestat cost control. The light passes a short-pass dichroic filter (<640 nm) (2) before it enters a 10 × 10 mm Perspex rod (3) that guides it to the 10 × 10 mm glass cuvette (4), mixing the various light qualities by multiple reflections. The suspension within the cuvette (4) is continuously stirred with the help of a small magnetic “flea.