The novel information provided by the new device is contained in the wavelength-dependent selleck chemicals parameter Sigma(II)λ, the definition of which for technical–methodological reasons differs from the parameter σPSII used by researchers in limnology and oceanography (Koblizek et al. 2001; Kolber et al. 1998). Almost all σPSII values reported in the literature were determined for one color of light, irrespective of the pigment-composition of the investigated sample. Furthermore, σPSII has been measured in widely differing states of the sample, with the PS II acceptor
side being more or less reduced, which leads to corresponding changes in the sigmoidicity and time constant of the light-induced fluorescence rise. In contrast, Sigma(II)λ is selleck products always measured in a defined quasi-dark reference state, at close to maximal efficiency of PS II. Any changes of the sample with respect to this reference state, e.g., by light-driven down-regulation or photodamage of PS II, do not affect Sigma(II)λ, 4SC-202 but are contained in the effective PS II quantum yield, Y(II), which is lowered with respect
to the PS II quantum yield, Y(II)max, measured in the reference state, in which also Sigma(II)λ was measured. Therefore, the values of Sigma(II)λ obtained for Chlorella and Synechocystis are substantially higher than the σPSII values reported, e.g., by Koblizek et al. (2001).
Other new parameters introduced for Baf-A1 price work with the multi-color-PAM are PAR(II) and ETR(II), which describe the absolute rates of photon absorption by PS II and electron transport via PS II, respectively. PAR(II) just like Sigma(II)λ is defined for a quasi-dark reference state. With this approach, fluorescence-based estimation of absolute photosynthetic electron transport rates in optically thin suspensions has been given a reliable methodological basis. Related work using the parameter σPSII can be found almost exclusively in the limnology and oceanography literature, which partially may be due to the complexity of its definition, understanding of which requires considerable background knowledge. Comparison of Figs. 4 and 8 demonstrates convincingly that quantitative information on the functional PS II absorption cross section is of general importance for quantitative assessment of photosynthetic activity, which becomes very evident as soon as different colors of light are applied. It may be foreseen that the multi-color-PAM will stimulate future research of the wavelength dependence of photosynthesis not only in suspensions of algae and cyanobacteria but also in whole leaves, macrophytes or even corals and other organisms containing endosymbionts.