Evidence for a fluorescence yield change driven by a light-induced conformational change within photosystem II during the fast chlorophyll a fluorescence rise

Abstract

Experiments were carried out to identify a process co-determining with Q(A) the fluorescence rise between F(0) and F(M). With 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU), the fluorescence rise is sigmoidal, in its absence it is not. Lowering the temperature to -10°C the sigmoidicity is lost. It is shown that the sigmoidicity is due to the kinetic overlap between the reduction kinetics of Q(A) and a second process; an overlap that disappears at low temperature because the temperature dependences of the two processes differ. This second process can still relax at -60°C where recombination between Q(A)(-) and the donor side of photosystem (PS) II is blocked. This suggests that it is not a redox reaction but a conformational change can explain the data. Without DCMU, a reduced photosynthetic electron transport chain (ETC) is a pre-condition for reaching the F(M). About 40% of the variable fluorescence relaxes in 100ms. Re-induction while the ETC is still reduced takes a few ms and this is a photochemical process. The fact that the process can relax and be re-induced in the absence of changes in the redox state of the plastoquinone (PQ) pool implies that it is unrelated to the Q(B)-occupancy state and PQ-pool quenching. In both +/-DCMU the process studied represents ~30% of the fluorescence rise. The presented observations are best described within a conformational protein relaxation concept. In untreated leaves we assume that conformational changes are only induced when Q(A) is reduced and relax rapidly on re-oxidation. This would explain the relationship between the fluorescence rise and the ETC-reduction.

Chlorophyll a fluorescence induction: a personal perspective of the thermal phase, the J–I–P rise

“…(3) While some of the alternative theories (e.g., Delosme 1967;Joliot 1979, 1981a, b;Schreiber et al 1989, Samson andBruce 1996;Schreiber 2002) are in agreement with the above-described feature (3) of the modified version of Duysens and Sweers Theory, others are not (e.g., Schreiber and Krieger 1996;Bulychev and Vredenberg 2001;Pospíšil and Dau 2002;Vredenberg 2008aVredenberg , 2011Schansker et al 2011). Indeed, in these last theories it is assumed that a non-photochemical fluorescence enhancement contributes to the maximum fluorescence F M , in addition to the contribution due to the complete Q A reduction in active PSII centers.…”

“…''Fast fluorescence induction: Early interpretations by L. N. M. Duysens, R. Delosme, and P. Joliot'' section) that only *50 % of the variable Chl a fluorescence is due to the photochemical closure of PSII RCs, and related to the redox state of Q A , while the other *50 % has a non-photochemical origin, and is related to the presence of a hypothetical secondary quencher R. Some of the arguments in favor of this type of theory listed by Schansker et al (2011) are:…”

“…The membrane potential (DW) is expected to affect Chl a fluorescence for various reasons, including the Stark effect (Diner and Joliot 1976;Graan and Ort 1983;Bulychev et al 1986;Bulychev and Niyazova 1989;Zheng et al 1990;Dau andSauer 1991, 1992;Bulychev and Vredenberg 1999;Pospíšil and Dau 2002;Bulychev 2002, 2003;Belyaeva et al 2003;Rubin and Riznichenko 2009;Antal et al 2011) (see ''Understanding the thermal phase: an integrated view'' section). (13) Conformational changes influencing the fluorescence yield have been suggested to take place during the fast FI (Bradbury and Baker 1983;Moise and Moya 2004a, b;Schansker et al 2011).…”

“…Therefore, in order to understand the relationship of Chl a fluorescence to various photosynthetic processes, parallel measurements of several reactions are expected to provide better insight into their mechanisms. In this sense, the development of instruments capable of measuring simultaneously the prompt fluorescence and several other types of signals, such as 820 nm transmission changes (related to the PSI activity), and the delayed fluorescence (in the ls-ms range, related to the back reactions of PSII), offers new opportunities for the improvement of the analysis of the relationship of fluorescence with other photosynthetic processes (Schreiber and Schliwa 1987;Schreiber et al 1988;Neubauer 1989, 1990;Schreiber 1998, 2008;Schreiber 2002Schreiber , 2004Schansker et al 2003Schansker et al , 2008Schansker et al , 2011Goltsev et al 2009). However, for a quantitative understanding of these Fig.…”

Fluorescence lifetime snapshots reveal two rapidly reversible mechanisms of photoprotection in live cells of Chlamydomonas reinhardtii

“…Actinic light was applied at T ¼ 0 s, where T is the time axis along which light adaptation occurs. During the first 0.3 s of actinic light illumination (Inset), the fluorescence yield increased as the plastoquinone pool became fully reduced, and PSII reaction centers became saturated (13). The induction of NPQ quenching pathways caused the fluorescence yield to rapidly decrease for 0.3 s < T < 2.5 s, decrease much less for 2.5 s < T < 10 s, and plateau by T ¼ 20 s at a yield slightly lower than the yield before actinic light was applied.…”