A Normalized F o/PAR versus peak wavelength of the ML. The data were normalized to unity at maximal relative F o/PAR, i.e., for 625 nm with Synechocystis. B Absorptance in the same suspensions plotted vs peak wavelength of the ML Table 1 Comparison of www.selleckchem.com/products/Cyt387.html F o and F o/PAR of dilute suspensions of Chlorella and Synechocystis measured with five different colors at WZB117 datasheet identical settings of ML-intensity and minimal pulse-frequency Parameter Peak wavelength (nm) 440 480 540 590 625 Incident PAR (μmol/(m2 s)) 0.0234 0.0309 0.0201 0.0099 0.0159 Incident PAR (rel. units) 75.7
100.0 65.2 32.0 51.5 F o(Chlorella)λ (V) 2.294 2.366 0.389 0.252 0.522 F o(Chlorella)λ/PAR (rel. units) 0.917 0.716 0.181 0.238 0.307 F o(Synechocystis)λ (V) 0.359 0.198 0.616 0.703 1.702 F o(Synechocystis)λ/PAR (rel. units) 0.143 0.060 0.286 0.665 1.000 The F o/PAR values were normalized to give 1 rel. unit at 625 nm with Synechocystis, where the maximal signal was obtained As may be expected in view of the differences in photosynthetic pigments serving PS II, the wavelength dependence of dark-fluorescence yield, F o,
differs considerably between Chlorella and Synechocystis. Somewhat unexpectedly, despite the identical absorptance at 440 nm, i.e., although the same fraction of incident 440 nm quanta is absorbed in the Chlorella and Synechocystis suspensions, the F o(Chlorella)440 exceeds the F o(Synechocystis)440 by a factor of 2.294/0.359 = 6.4 (see Table 1). Absorption at 440 nm Selleck SHP099 is dominated by Chl a and, hence, Chl a concentration should be close to identical in the two samples. The large difference in F o/PAR values may be explained by a higher fluorescence yield of Chl a (PS II) as compared to Chl a (PS I) and to a higher PS I/PS II ratio in Synechocystis than in Chlorella. In contrast, when with the same
samples 625 nm ML is used, the F o(Synechocystis)625 exceeds the F o(Chlorella)625 by a factor of 1.702/0.522 = 3.3. In Synechocystis, the peak of absorption by phycocyanin is at 625 nm, whereas in Chlorella this wavelength is at some distance from the main Chl a/b absorption peaks. The F o/PAR plots of Chlorella and Synechocystis in Fig. 3A can be compared with the corresponding absorptance spectra in Fig. 3B, many measured under identical optical conditions (see “Materials and methods”). While the spectra of F o/PAR and absorptance resemble each other with Chlorella, they differ substantially in the case of Synechocystis. PS I-specific absorption is higher in Synechocystis than in Chlorella due to a higher PS I/PS II ratio. Also, the more PS I-specific absorption differs from PS II-specific absorption, the more the overall absorptance spectrum will differ from the F o/PAR spectrum. Therefore, F o/PAR spectra can provide more specific information on PS II absorption, than absorptance spectra.