0, as compared to 5.1 of the corresponding F o/PAR. This finding confirms that Sigma(II)λ is a more specific measure of PS II excitation than F o/PAR. While F o may contain more or less non-PS II fluorescence, depending

on excitation wavelength and organism, variable fluorescence yield and the rate with which it is induced, are specific for PS II. Another important difference between Sigma(II) and F o/PAR is that Sigma(II) gives absolute information on the functional absorption cross section of PS II, which is independent of Chl content, whereas F o/PAR is proportional to both Chl content and functional cross section of PS II. Furthermore, F o/PAR depends on ML-intensity and gain parameters, which have no influence on Sigma(II), as measured with the multi-color-PAM. Fig. 7 Functional cross section of PS II, Sigma(II) as a function of AL-color in dilute suspensions buy FG-4592 (300 μg Chl/L) of Chlorella and Synechocystis, derived from automated Elafibranor research buy measurements of five consecutive O–I 1 rise curves each (Script-files Sigma1000Chlor_10.prg and Sigma1000Sycy_10.prg) in the presence of FR background light. Time between consecutive O–I 1 measurements, 10 s. Sigma(II) values derived by dedicated PamWin-3 fitting routine (see

text and Table 2) Definition of PAR(II) and ETR(II) The wavelength-dependent rate, with which photons (or quanta) are absorbed by PSII, is directly reflected in the k(II) determined https://www.selleckchem.com/products/pf-04929113.html by fitting the O–I 1 rise kinetics measured at high PAR under defined control conditions (see text accompanying Fig. 6). There is direct correspondence cAMP inhibitor between the PS II turnover rate, k(II), in units of electrons/(PS II s) and the quantum absorption rate at PS II reaction centers in units of

quanta/(PS II s). We propose the name PAR(II) for the latter, with the general definition derived from Eq. 1 (see “Materials and methods”) $$ \textPAR(\textII) = k(\textII) = \textSigma(\textII)_\lambda \cdot L \cdot \textPAR, $$ (3)where k(II) is the rate constant of PS II turnover, Sigma(II)λ is the functional cross section of PS II (in units of nm2), L is Avogadro’s constant (with the dimension of mol−1), PAR is quantum flux density (or photon fluence rate) and PAR(II) is the rate of quantum absorption in PS II, in units of quanta/(PS II s). In practice, calculation of PAR(II) from PAR is quite simple when Sigma(II)λ is known: the numerical value of PAR (in units of μmol quanta/(m2 s)) just has to be multiplied by 0.6022 × Sigma(II)λ. Hence, once Sigma(II) has been determined for a particular color and sample (via measurement of the O–I 1 rise kinetics at a defined high light intensity), PAR(II) can be derived for any other PAR (at constant color and state of the sample), without further measurements of fast kinetics. In the case of Chlorella, with Sigma(II)625 = 1.669 (see Table 2), PAR(II) practically equals PAR, as 0.6022 × 1.669 happens to be very close to unity.