Vredenberg and co-workers (Vredenberg 2000; Vredenberg et al. 2006) developed another interpretation model, in which, in addition to Q A − , the IP phase is determined by the electric field, and JI rise reflects an inactivation of PSII RCs (associated with proton transport over the membrane) in which Pheo− can accumulate. These alternative interpretations were challenged https://www.selleckchem.com/products/Trichostatin-A.html by Stirbet and Govindjee (2012). The first assumption that the F O-to-F

M rise is a reflection of the reduction of Q A implies that it should always be possible to reach F M, since all Q A can be reduced if the light intensity is high enough (i.e., when the excitation rate is much higher than re-oxidation rate of Q A − by forward electron transport and/or the exchange of PQH2

for PQ at the Q B-site). However, Schreiber (1986), Samson and Bruce (1996) and Schansker et al. (2006, 2008) showed in several ways that this is not the case. A second, related, assumption is that there are no changes in non-photochemical quenching during a saturating pulse. Finally, a third assumption is that the parameters F V/F M and ΦPSII are measures of the PSII quantum 3-Methyladenine purchase yield and that ΦPSII can be used to calculate the photosynthetic electron transport rate. For ΦPSII, this assumption has been partially verified experimentally, showing under several conditions a linear correlation between the calculated photosynthetic electron transport rate and the CO2 assimilation rate (Genty et al. 1989; Krall and Edwards 1992 and see Questions 29 and 30). We note that the meaning of the parameter F V/F M has not been derived SB-715992 supplier experimentally but is click here based on an analysis of so-called competitive rate equations (fluorescence emission competes with other processes like heat emission and photosynthesis) for the F O and F M states (Kitajima and Butler 1975; Kramer et al. 2004). This

analysis is correct as long as the fluorescence rise between F O and F M is determined by the reduction of Q A only (see Schansker et al. 2014 for a discussion of this point). Question 22. Are there naturally occurring fluorescence quenchers other than Q A? Another fluorescence quencher that has been described extensively is P680+ (Butler 1972; Zankel 1973; Shinkarev and Govindjee 1993; Steffen et al. 2005). The short lifetime of P680+ keeps the population of this quencher low under most conditions. Simulation work has shown that under high light conditions, the highest concentration should occur around the J-step (Lazár 2003), which was supported by experimental observations (Schansker et al. 2011). However, P680+ quenching does not affect the F O and F M levels. Oxidized PQ molecules can also quench fluorescence, but only in isolated thylakoids and in PSII-enriched membranes (Vernotte et al. 1979; Kurreck et al. 2000; Tóth et al. 2005a) and not in leaves (Tóth et al. 2005a).