Spectroscopic characterization of triplet forming states in photosystem II

Vass, Imre; Styring, Stenbjörn

doi:10.1021/bi00141a002

Cited by 40 publications

(31 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been suggested previously that HCO-could be involved in protonation of PSII quinone acceptors (28,29). Protonation of reduced QA improves the yield of charge separation owing to the removal of the electrostatic repulsion between Pheo-and QA (30)(31)(32) (32). A better recovery of variable fluorescence and variable thermal dissipation is obtained when Co is added together with Mn and HCO3 in the reconstitution medium (Fig.…”

Section: Methodsmentioning

confidence: 84%

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Allakhverdiev

Klimov

Carpentier

1994

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

In photosynthetic systems, the absorbed light energy is used to generate electron transport or it is lost in the form of fluorescence and thermal emission. While fluorescence can be readily measured, the detection of thermal deactivation processes can be achieved by the photoacoustic technique. In that case, the pressure wave generated by the thermal deactivations in a sample irradiated with modulated light is detected by a sensitive microphone. The relationships between the yield of fluorescence and thermal emissions measured simultaneously were analyzed by using a spinach photosystem II (PSH)-enriched preparation. It is shown that the quenching of fluo- In the photosynthetic apparatus, the absorbed light energy is either used to generate electron transport that is initiated by charge separation at the level of photosystems I and II (PSI and PSII), or the energy is lost through fluorescence and thermal emission. Fluorescence can be readily measured, but photoacoustic (PA) spectroscopy has been advantageously used to study the thermal deactivation processes in photosynthetic materials (1). In that case, a solid or semisolid sample is irradiated with modulated light in a closed cell. The thermal deactivations generate a periodic heat flow in the The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. surrounding gas medium that produces a pressure wave transduced into an electric signal by a sensitive microphone. Most usefully, the difference between the thermal emission yields ofactive and inactive samples allows the determination of the photochemical energy-storage yield (2). In most studies, the inactive sample with closed reaction centers was obtained by superimposition of a nonmodulated background light of saturating intensity on the low-intensity modulated measuring beam (3-6). The energy-storage yield has been correlated with the electron transport status (7,8), and it was suggested that electron transfer from water to the plastoquinone (PQ) pool was responsible for the stored energy (8-10).Similarly, part of the fluorescence emission (the so-called variable fluorescence) is closely related to the redox state of the secondary acceptors QA and QB in PSII and therefore is greatly influenced by the electron transport status (11). Thus, a strong interdependence between the yield of energy storage and the yield of variable fluorescence can be suggested (10). The correlation between chlorophyll (Chl) fluorescence and the PA signal has been studied in intact leaves (12, 13). However, the interpretations were complicated by the participation of PSI in the thermal signal and by a photobaric contribution due to oxygen evolution.A PSII submembrane fraction depleted of PSI should constitute the simplest model to study the relationship between variable fluorescence emission and thermal energy storage. The thermal emission behavior of such preparations has been...

show abstract

Section: Methodsmentioning

confidence: 84%

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Allakhverdiev

Klimov

Carpentier

1994

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…Taking into account the increase in the closed PS 2 and centers with impaired OEC function in SD cells, the PS 2 inactivation may be interpreted as being due to both acceptor and donor sides contribution. The first can be related to the protonation and loss of Q A (Vass and Styring 1992) stimulated by the excessive reduced state of plastoquinones in SD cells due to the sharp decline in the linear electron flow and increased electron transport from stroma to the PQ pool (Melis et al 2000;, while the mechanisms of the OEC dysfunction is not clear and remains to be clarified in future studies. The demonstrated disruption of energy dissipation mechanisms may enhance photoinhibition of primary photosynthetic components.…”

Section: Resultsmentioning

confidence: 99%

Study of photosystem 2 heterogeneity in the sulfur-deficient green alga Chlamydomonas reinhardtii

2007

View full text Add to dashboard Cite

A set of chlorophyll fluorescence methods, including PEA (Plant Efficiency Analyser), PAM (Pulse Amplitude Modulated fluorometer), and picosecond fluorometer, was employed to study PS 2 heterogeneity in sulfur deprived green algae Chlamydomonas reinhardtii. The regression method and JIP test were applied to analyze chlorophyll fluorescence kinetics. The fractions of PS 2 characterized by the energetic disconnection, smaller antenna size, elevated constant rate of primary photochemistry, and inability to maintain DeltapH-dependent energy dissipation increased essentially already after 12 h of incubation in sulfur depleted medium. The amount of PS 2 centers with reduced QA (closed state), QB-non-reducing centers with impaired water splitting function, and centers coupled to the plastoquinone pool with the slow cycle rate increased dramatically after 24 h period of deprivation. The mechanisms of PS 2 inactivation under sulfur deprivation are discussed.

show abstract

“…To explain our observations we wish to propose a model that recognizes that cyt b559 can exist in a high and low potential form and that both donor and acceptor side photoinhibitory processes occur. We also assume that there is only one cyt b559 per functional PSII in the thylakaid membrane for which there is now very strong experimental evidence (41,45 (12,13), cyt b559 could shift its potential to the low potential form. Such a shift in response to strong illumination has already been observed (27) and was faster than the subsequent appearance of photoinhibitory damage.…”

Section: Discussionmentioning

confidence: 99%

“…Donor side photoinhibition is readily seen when the water-splitting reactions have been inhibited (9)(10)(11). Acceptor side photoinhibition occurs when there is an overreduction ofthe quinone pool and QA becomes doubly reduced (12,13). In this event, there is an increase in the probability ofcharge recombination between the primary radical pair P680+ Pheo-leading to the triplet state of P680.…”

mentioning

confidence: 99%

A functional model for the role of cytochrome b559 in the protection against donor and acceptor side photoinhibition.

Barber

Rivas

1993

Proc. Natl. Acad. Sci. U.S.A.

149

View full text Add to dashboard Cite

A quinone-independent photoreduction of the low potential form of cytochrome b559 has been studied using isolated reaction centers of photosystem II. Under anaerobic conditions, the cytochrome can be fully reduced by exposure to strong illumination without the addition of any redox mediators. Under high light conditions, the extent and rate of the reduction is unaffected by addition of the exogenous electron donor Mn2+ and, during this process, no irreversible damage occurs to the reaction center. However, prolonged illumination in strong light brings about irreversible bleaching of chlorophyll, indicative of photoinhibitory damage. When the cytochrome is fully reduced and excess Mn2+ is present, the effect of moderate light is to facilitate the photoaccumulation of reduced pheophytin. The dark reoxidation of the reduced cytochrome is very slow under anaerobic conditions but significantly speeded up on addition of oxidized 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone. From these results it is suggested that the low potential form of cytochrome b559 can accept electrons directly from reduced pheophytin and in so doing help to protect the reaction center against acceptor side photoinhibition as suggested by Nedbal et al. [Nedbal, J., Samson, G. & Whitmarsh, J. (1992) Proc. Natl. Acad. Sci. USA 89, 7929-7933]. This conclusion has been incorporated into a model that further suggests that in its high potential form the cytochrome primarily acts to protect against donor side photoinhibition due to increased lifetime of highly oxidized species as previously proposed by Thompson and Brudvig [Thompson, L. & Brudvig, G. W. (1988) Biochemistry 27, 6653-6658]. The particular feature of our scheme is that it incorporates reversible interconversion between the two redox forms so as to protect against either type of photoinhibition.

show abstract

Spectroscopic characterization of triplet forming states in photosystem II

Cited by 40 publications

References 29 publications

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Variable thermal emission and chlorophyll fluorescence in photosystem II particles.

Study of photosystem 2 heterogeneity in the sulfur-deficient green alga Chlamydomonas reinhardtii

A functional model for the role of cytochrome b559 in the protection against donor and acceptor side photoinhibition.

Contact Info

Product

Resources

About