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The aim of the study was to determine the effectiveness of regularly applied biological control by continuous monitoring of pests with the help of color traps (sticky sheets) and flower tests with joint species identification of the useful insect to determine the extent to which native useful insects can settle next to the introduced predatory ones. The latter process is to be facilitated by growing a flowering mixture of annual plants at one of the experimental sites, which provides adequate feeding and hiding place for beneficial insects.The experiment was performed in one pepper forcing period. The main pest insects are: western flower thrips (Frankliniella occidentalis), tobacco thrips (Thrips tabaci).Useful insects in the experiment: predatory mites (Amblyseius spp.) and predatory flower bugs (Orius laevigatus).

A felelős vállalatirányítás koncepciója több évtizede jelen van mégis, az elmélet gyakorlatba való átültetése több szempontból is féloldalasra sikerült. Jelen tanulmányban a magyarországi vállalatok jelenlegi helyzetét és eredményeit tekintem át.

A biomassza könnyen hozzáférhető, megújuló és környezetbarát energiaforrás. A megújuló szerves anyagok energetikai célú felhasználása világszerte növekvő tendenciát mutat igy Magyarországon is. Az erdészeti ültetvények, melyek különböző, nagyszámú, gyorsan növő lombhullató fafajtát tartalmaznak és homogén, helyileg rendelkezésre álló nyersanyagot tudnak biztosítani, széles körben elterjedtek. Kutatásaink során egy rövid vágásfordulójú energetikai faültetvény pénzügyi életképességét vizsgáltuk a kunsági régióban. Mind az EU, mind Magyarország gazdaságilag ösztönzi a bioenergia-termelő létesítmények létrehozását. Eredményeink azt mutatják, hogy a vizsgált vállalkozás nem termelt volna nyereséget támogatások nélkül. Számos akadály áll fenn a gazdálkodók előtt: például a kezdeti magas tőkeigény, a betakarítási módszerek technológiai hiányosságai, a magas logisztikai költségek, illetve az elfojtott értékesítési árak.

Településfejlesztési és vidékfejlesztési szempontból is fontos tényezőként jelenik meg napjainkban a tanyarendszer kérdése. Munkánkban a magyar Nagyalföld Duna-Tisza közén a legjelentősebb tanyás területet, a Homokhátságot vizsgáltuk. Az alföldi tanyákat funkciójuk szerint gazdasági, lakó és lakatlan funkciókra osztottuk, ezek arányát és jellemzőt mutatja be a tanulmányunk. A hagyományos funkcióval rendelkező mezőgazdasági termelésen alapuló tanyák Magyarországon teljes mértékben visszaszorultak. A legfontosabb változások a tisztán lakófunkció térnyerésében, a tanyák hobbitanyává válásában, a vendégfogadás, idegenforgalom megjelenésében jelennek meg, ezekhez társult az elhagyott, üres tanyák nagyszámú megjelenése. A tanyavilág ügye Magyarországon komplexen kezelendő téma, amelyben kormányzati szinten és a célirányos programok kidolgozásával kell megoldani.

Fluorescence yield relaxation following a light pulse was studied in various cyanobacteria under aerobic and microaerobic conditions. In Synechocystis PCC 6803 fluorescence yield decays in a monotonous fashion under aerobic conditions. However, under microaerobic conditions the decay exhibits a wave feature showing a dip at 30–50 ms after the flash followed by a transient rise, reaching maximum at ~ 1 s, before decaying back to the initial level. The wave phenomenon can also be observed under aerobic conditions in cells preilluminated with continuous light. Illumination preconditions cells for the wave phenomenon transiently: for few seconds in Synechocystis PCC 6803, but up to one hour in Thermosynechocystis elongatus BP-1. The wave is eliminated by inhibition of plastoquinone binding either to the QB site of Photosystem-II or the Qo site of cytochrome b6f complex by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, respectively. The wave is also absent in mutants, which lack either Photosystem-I or the NAD(P)H-quinone oxidoreductase (NDH-1) complex. Monitoring the redox state of the plastoquinone pool revealed that the dip of the fluorescence wave corresponds to transient oxidation, whereas the following rise to re-reduction of the plastoquinone pool. It is concluded that the unusual wave feature of fluorescence yield relaxation reflects transient oxidation of highly reduced plastoquinone pool by Photosystem-I followed by its re-reduction from stromal components via the NDH-1 complex, which is transmitted back to the fluorescence yield modulator primary quinone electron acceptor via charge equilibria. Potential applications of the wave phenomenon in studying photosynthetic and respiratory electron transport are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.

The green algae Chlamydomonas sp. MACC-549 and Chlamydomonas reinhardtii cc124 were investigated for their hydrogen-evolution capability in mixed algal–bacterial cultures. Stable bacterial contaminations were identified during the cultivation of Chlamydomonas sp. 549. The bacterial symbionts belonged to various genera, mostly Brevundimonas, Rhodococcus, and Leifsonia, each of which enhanced the algal hydrogen production. This phenomenon was not limited to natural associations. Increased algal hydrogen evolution was achieved by simple artificial algal–bacterial communities as well. Algal–bacterial cocultures were designed and tested in hydrogen evolution experiments. The highest hydrogen yields were obtained when hydrogenase-deficient Escherichia coli was used as a symbiotic bacterium (Chlamydomonas sp. 549 generated 1196.06 ± 4.42 μL H2 L−1, while C. reinhardtii cc124 produced 5800.54 ± 65.73 μL H2 L−1). The results showed that oxygen elimination is the most crucial factor for algal hydrogen production and that efficient bacterial respiration is essential for the activation of algal Fe-hydrogenase. The algae-based hydrogen evolution method described represents a novel combination of fermentative and photolytic hydrogen generation processes. Active photosynthesis was maintained during the entire hydrogen evolution process, which contributes to the sustainability of hydrogen production.

The Mn(4)CaO(5) cluster of photosystem II (PSII) catalyzes the oxidation of water to molecular oxygen through the light-driven redox S-cycle. The water oxidizing complex (WOC) forms a triad with Tyrosine(Z) and P(680), which mediates electrons from water towards the acceptor side of PSII. Under certain conditions two other redox-active components, Tyrosine(D) (Y(D)) and Cytochrome b(559) (Cyt b(559)) can also interact with the S-states. In the present work we investigate the electron transfer from Cyt b(559) and Y(D) to the S(2) and S(3) states at 195 K. First, Y(D)(•) and Cyt b(559) were chemically reduced. The S(2) and S(3) states were then achieved by application of one or two laser flashes, respectively, on samples stabilized in the S(1) state. EPR signals of the WOC (the S(2)-state multiline signal, ML-S(2)), Y(D)(•) and oxidized Cyt b(559) were simultaneously detected during a prolonged dark incubation at 195 K. During 163 days of incubation a large fraction of the S(2) population decayed to S(1) in the S(2) samples by following a single exponential decay. Differently, S(3) samples showed an initial increase in the ML-S(2) intensity (due to S(3) to S(2) conversion) and a subsequent slow decay due to S(2) to S(1) conversion. In both cases, only a minor oxidation of Y(D) was observed. In contrast, the signal intensity of the oxidized Cyt b(559) showed a two-fold increase in both the S(2) and S(3) samples. The electron donation from Cyt b(559) was much more efficient to the S(2) state than to the S(3) state.

In the present study we investigated the role of the PsbU subunit in the electron transport characteristics and light sensitivity of the Photosystem II complex. The experiments were performed by using an earlier characterized PsbU-less mutant of the cyanobacterium Synechococcus PCC 7942, which has enhanced antioxidant capacity (Balint et al. FEBS Lett. 580 (2006) 2117–2122). Flash induced Chl fluorescence measurements in the presence and absence of the electron transport inhibitor DCMU showed that both the S 2 Q A - and the S 2 Q B - recombination is slowed down in the PsbU mutant relative to the WT strain. Thermoluminescence measurements confirmed the increased stability of the S 2 Q A - and S 2 Q B - charge pairs by showing an increased peak temperature of Q and B bands, which were measured in the presence and absence of DCMU, respectively. In addition, the intensity of the TL bands is also increased in the PsbU mutant (≈1.7 times for the B band), as compared to the WT. The PsbU mutant shows enhanced loss of Photosystem II activity under exposure to high light intensity both in the absence and presence of the protein synthesis inhibitor lincomycin. It is concluded from the data that the lack of the PsbU subunit in Synechococcus PCC 7942 affects the energetic stability of the S 2 Q A - and S 2 Q B - charge pairs by modifying both the PSII donor and acceptor side components. This effect is most likely caused by structural changes in the vicinity of the Mn cluster and in the inner part of the PSII complex, which are induced by the lack of the PsbU subunit from the lumenal part of the complex. The light sensitivity of Photosystem II in Synechococcus 7942 in the absence of the PsbU subunit is likely due to reactive oxygen species, which are produced as a consequence of disturbed donor side structure and/or due to the modified energetic properties of the primary radical pair.

Coral bleaching is an important environmental phenomenon, whose mechanism has not yet been clarified. The involvement of reactive oxygen species (ROS) has been implicated, but direct evidence of what species are involved, their location and their mechanisms of production remains unknown. Histidine-mediated chemical trapping and singlet oxygen sensor green (SOSG) were used to detect intra- and extracellular singlet oxygen ((1) O2 ) in Symbiodinium cultures. Inhibition of the Calvin-Benson cycle by thermal stress or high light promotes intracellular (1) O2 formation. Histidine addition, which decreases the amount of intracellular (1) O2 , provides partial protection against photosystem II photoinactivation and chlorophyll (Chl) bleaching. (1) O2 production also occurs in cell-free medium of Symbiodinium cultures, an effect that is enhanced under heat and light stress and can be attributed to the excretion of (1) O2 -sensitizing metabolites from the cells. Confocal microscopy imaging using SOSG showed most extracellular (1) O2 around the cell surface, but it is also produced across the medium distant from the cells. We demonstrate, for the first time, both intra- and extracellular (1) O2 production in Symbiodinium cultures. Intracellular (1) O2 is associated with photosystem II photodamage and pigment bleaching, whereas extracellular (1) O2 has the potential to mediate the breakdown of symbiotic interaction between zooxanthellae and their animal host during coral bleaching.

The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxidizing complex (Ferreira, K.N., Iverson, T.M., Maghlaoui, K., Barber, J. & Iwata, S. (2004) Science 303, 1831-1838). However, its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of the D1-H333E, D1-H332D and D1-H332S mutations on the electron transport of Photosystem II in intact cells of the cyanobacterium Synechocystis 6803. Although the mutants are not photoautotrophic they all show flash-induced thermoluminescence and chlorophyll fluorescence, which originate from the S(2)Q(A) (-) and S(2)Q(B) (-) recombinations demonstrating that charge stabilization takes place in the water oxidizing complex. However, the conversion of S(2) to higher S states is inhibited and the energetic stability of the S(2)Q(A) (-) charge pair is increased by 75, 50 and 7 mV in the D1-H332D, D1-H332E and D1-H332S mutants, respectively. This is most probably caused by a decrease of E(m)(S(2)/S(1)). Concomitantly, the rate of electron donation from Mn to Tyr-Z(b) during the S(1) to S(2) transition is slowed down, relative to the wild type, 350- and 60-fold in the D1-H332E and D1-H332D mutants, respectively, but remains essentially unaffected in D1-H332S. A further effect of the D1-H332E and D1-H332D mutations is the retardation of the Q(A) to Q(B) electron transfer step as an indirect consequence of the donor side modification. Our data show that although the His residue in the D1-332 position can be substituted by other metal binding residues for binding photo-oxidisable Mn it is required for controlling the functional redox energetics of the Mn cluster.

Despite many years of study, the physiological role of cytochrome b-559 (Cyt b-559) within the photosystem II (PSII) complex still remains unclear. Here we describe the analysis of a mutant of the green alga Chlamydomonas reinhardtii in which the His ligand to the haem, provided by the alpha subunit, has been replaced by a Cys residue. The mutant is unable to grow photoautotrophically but can assemble oxygen-evolving PSII supercomplexes to 15-20% of the levels found in the wild-type control. Haem is still detected in the isolated PSII supercomplexes but at sub-stoichiometric levels consistent with weaker binding to the mutated cytochrome. Analysis of PSII activity in cells indicates slowed electron transfer in the mutant between plastoquinones QA and QB. We show that PSII activity in the mutant is more sensitive to chronic photoinhibition than the WT control because of two effects: a faster rate of damage and an impaired PSII repair cycle at the level of synthesis and/or incorporation of D1 into PSII. We also demonstrate that Cyt b-559 plays a role during the critical stage of assembling the Mn4CaO5 cluster. Overall we conclude that Cyt b-559 optimises electron transfer on the acceptor side of PSII and plays physiologically important roles in the assembly, repair and maintenance of the complex.

Electron paramagnetic resonance (EPR) spectroscopy is one of the major techniques used to analyse the structure and function of the water oxidising complex (WOC) in Photosystem II. The discovery of an EPR signal from the S0 state has opened the way for new experiments, aiming to characterise the S0 state and elucidate the differences between the different S states. We present a review of the biochemical and biophysical characterisation of the S0 state multiline signal that has evolved since its discovery, and compare these results to previous and recent data from the S2 multiline signal. We also present some new data from the S2 state reached on the second turnover of the enzyme.

We have studied the pH effect on the S(0) and S(2) multiline electron paramagnetic resonance (EPR) signals from the water-oxidizing complex of photosystem II. Around pH 6, the maximum signal intensities were detected. On both the acidic and alkaline sides of pH 6, the intensities of the EPR signals decreased. Two pKs were determined for the S(0) multiline signal; pK(1) = 4.2 +/- 0.2 and pK(2) = 8.0 +/- 0.1, and for the S(2) multiline signal the pKs were pK(1) = 4.5 +/- 0.1 and pK(2) = 7.6 +/- 0.1. The intensity of the S(0)-state EPR signal was partly restored when the pH was changed from acidic or alkaline pH back to pH approximately 6. In the S(2) state we observed partial recovery of the multiline signal when going from alkaline pH back to pH approximately 6, whereas no significant recovery of the S(2) multiline signal was observed when the pH was changed from acidic pH back to pH approximately 6. Several possible explanations for the intensity changes as a function of pH are discussed. Some are ruled out, such as disintegration of the Mn cluster or decay of the S states and formal Cl(-) and Ca(2+) depletion. The altered EPR signal intensities probably reflect the protonation/deprotonation of ligands to the Mn cluster or the oxo bridges between the Mn ions. Also, the possibility of decreased multiline signal intensities at alkaline pH as an effect of changed redox potential of Y(Z) is put forward.

The chloroplast gene psbH encodes a 9-10 kDa thylakoid membrane protein (PSII-H) that is associated with photosystem II and is subject to light-dependent phosphorylation at a threonine residue located on the stromal side of the membrane. The function of PSII-H is not known, neither is it clear what regulatory role phosphorylation may play in the control of PSII activity. Using particle gun-mediated transformation, we have created chloroplast transformants of Chlamydomonas reinhardtii in which the synthesis of PSII-H is prevented by the disruption of psbH, or in which the phosphorylatable threonine is replaced by alanine through site-directed mutagenesis of the gene. The mutants lacking PSII-H have a photosystem II-deficient phenotype, with no detectable functioning PSII complex present in whole cells or isolated thylakoid membranes. In contrast, the alanine mutant (T3A) grows photoautotrophically, and PSII activity is comparable to wild-type cells as determined by various biochemical and biophysical assays. (C) 1998 Elsevier Science B.V.

PURPOSE: To determine the lower limit of dose reduction with hybrid and fully iterative reconstruction algorithms in detection of endoleaks and in-stent thrombus of thoracic aorta with computed tomographic (CT) angiography by applying protocols with different tube energies and automated tube current modulation. MATERIALS AND METHODS: The calcification insert of an anthropomorphic cardiac phantom was replaced with an aortic aneurysm model containing a stent, simulated endoleaks, and an intraluminal thrombus. CT was performed at tube energies of 120, 100, and 80 kVp with incrementally increasing noise indexes (NIs) of 16, 25, 34, 43, 52, 61, and 70 and a 2.5-mm section thickness. NI directly controls radiation exposure; a higher NI allows for greater image noise and decreases radiation. Images were reconstructed with filtered back projection (FBP) and hybrid and fully iterative algorithms. Five radiologists independently analyzed lesion conspicuity to assess sensitivity and specificity. Mean attenuation (in Hounsfield units) and standard deviation were measured in the aorta to calculate signal-to-noise ratio (SNR). Attenuation and SNR of different protocols and algorithms were analyzed with analysis of variance or Welch test depending on data distribution. RESULTS: Both sensitivity and specificity were 100% for simulated lesions on images with 2.5-mm section thickness and an NI of 25 (3.45 mGy), 34 (1.83 mGy), or 43 (1.16 mGy) at 120 kVp; an NI of 34 (1.98 mGy), 43 (1.23 mGy), or 61 (0.61 mGy) at 100 kVp; and an NI of 43 (1.46 mGy) or 70 (0.54 mGy) at 80 kVp. SNR values showed similar results. With the fully iterative algorithm, mean attenuation of the aorta decreased significantly in reduced-dose protocols in comparison with control protocols at 100 kVp (311 HU at 16 NI vs 290 HU at 70 NI, P ≤ .0011) and 80 kVp (400 HU at 16 NI vs 369 HU at 70 NI, P ≤ .0007). CONCLUSION: Endoleaks and in-stent thrombus of thoracic aorta were detectable to 1.46 mGy (80 kVp) with FBP, 1.23 mGy (100 kVp) with the hybrid algorithm, and 0.54 mGy (80 kVp) with the fully iterative algorithm.

By using two strains of Arthrospira (Spirulina)platensis, an economically important filamentous cyanobacterium, we compared the impairment of PSII activity and loss of D1 protein content under UV-B radiation. Our study showed that UV-B radiation induced a gradual loss of the oxygen-evolving activity to about 56% after 180 min UV-B irradiation both in strains 439 and D-0083, which have been kept under indoor and an outdoor culturing conditions, respectively for a prolonged period of time. The loss of oxygen evolution was accelerated in both strains in the presence of lincomycin, an inhibitor of protein synthesis, and the amount of D1 protein showed a decrease comparable to that of oxygen evolution during the UV-B exposure. However, the UV-B induced loss of oxygen-evolving activity and D1 protein amount was largely prevented when A. platensis cells were exposed to UV-B irradiance supplemented with visible light. Comparison of the two strains also showed a smaller extent of D1 protein synthesis dependent PSII repair in the indoor strain. Our results show that turnover of the D1 protein is an important defense mechanism to counteract the UV-B induced damage of PSII in A. platensis, and also that visible light plays an important role in maintaining the function of PSII under simultaneous exposure to UV-B and visible light.

The D1 protein (PsbA) of photosystem II (PSII) from Thermosynechococcus elongatus is encoded by a psbA gene family that is typical of cyanobacteria. Although the transcription of these three genes has been studied previously (Kós, P. B., Deák, Z., Cheregi, O., and Vass, I. (2008) Biochim. Biophys. Acta 1777, 74-83), the protein quantification had not been possible due to the high sequence identity between the three PsbA copies. The successful establishment of a method to quantify the PsbA proteins on the basis of reverse phase-LC-electrospray mass ionization-MS/MS (RP-LC-ESI-MS/MS) enables an accurate comparison of transcript and protein level for the first time ever. Upon high light incubation, about 70% PsbA3 could be detected, which closely corresponds to the transcript level. It was impossible to detect any PsbA2 under all tested conditions. The construction of knock-out mutants enabled for the first time a detailed characterization of both whole cells and also isolated PSII complexes. PSII complexes of the ΔpsbA1/psbA2 mutant contained only copy PsbA3, whereas only PsbA1 could be detected in PSII complexes from the ΔpsbA3 mutant. In whole cells as well as in isolated complexes, a shift of the free energy between the redox pairs in the PsbA3 complexes in comparison with PsbA1 could be detected by thermoluminescence and delayed fluorescence measurements. This change is assigned to a shift of the redox potential of pheophytin toward more positive values. Coincidentally, no differences in the Q(A)-Q(B) electron transfer could be observed in flash-induced fluorescence decay or prompt fluorescence measurements. In conclusion, PsbA3 complexes yield a better protection against photoinhibition due to a higher probability of the harmless dissipation of excess energy.

The psbO gene product of Photosystem II (PS II), the so-called 33 kDa extrinsic protein, is believed to be closely associated with the catalytic Mn cluster responsible for light-induced water oxidation. However, this protein is not absolutely required for water-splitting and its precise role remains to be clarified. We have used flash-induced thermoluminescence and oxygen evolution measurements to characterize the process of water oxidation in the IC2 mutant of Synechocystis sp. PCC 6803 from which the psbO gene had been deleted by Mayes et al. (Mayes, S.R., Cook, K.M., Self, S.J., Zhang, Z. and Barber J, (1991) Biochim. Biophys. Acta 1060, 1–12). The thermoluminescence results show that the extent of charge stabilization in the S 2 Q A and S 2 Q B states is reduced in the IC2 mutant to about 25–30% of that observed in the wild-type, suggesting that functional oxygen evolution occurs in a proportion of the psbO -less mutant cells. The stability of the S 2 Q A , but not that of the S 2 Q B , charge pair is markedly increased in the mutant. This points to a structural change of the PS II reaction center complex in the absence of the psbO gene product which affects the redox properties of the Q A and Q B acceptors to a different extent. The flash-induced oscillation of the B thermoluminescence band, arising from the S 2 Q B and S 3 Q B charge recombinations, is largely dampened in the mutant. This indicates that the ability of the water-oxidizing complex to reach its higher oxidation states, S 3 and S 4 , is limited when the psbO gene product is absent. In agreement with the thermoluminescence results, flash-induced oxygen evolution shows a decreased yield and largely dampened oscillation pattern in the mutant. These results indicate that although the psbO gene product is not an absolute requirement for water oxidation its absence disturbs the redox cycling of the water-oxidizing complex and retards the formation of its higher S states. The rapid loss of thermoluminescence intensity during strong illumination of the mutated organism confirms its high susceptibility to photoinhibition. This effect is most likely the consequence of the limited rate of electron donation from the psbO -less water-oxidizing complex to the PS II reaction centre where the accumulation of highly oxidizing species may damage their pigment and protein surroundings.

† Background and Aims Photosystem II of oxygenic organisms is a multi-subunit protein complex made up of at least 20 subunits and requires Ca 2þ and Cl 2 as essential co-factors. While most subunits form the catalytic core responsible for water oxidation, PsbO, PsbP and PsbQ form an extrinsic domain exposed to the luminal side of the membrane. In vitro studies have shown that these subunits have a role in modulating the function of Cl 2 and Ca 2þ , but their role(s) in vivo remains to be elucidated, as the relationships between ion concentrations and extrinsic polypeptides are not clear. With the aim of understanding these relationships, the photosynthetic apparatus of the extreme halophyte Salicornia veneta has been compared with that of spinach. Compared to glycophytes, halophytes have a different ionic composition, which could be expected to modulate the role of extrinsic polypeptides. † Methods Structure and function of in vivo and in vitro PSII in S. veneta were investigated and compared to spinach. Light and electron microscopy, oxygen evolution, gel electrophoresis, immunoblotting, DNA sequencing, RT– PCR and time-resolved chlorophyll fluorescence were used. † Key Results Thylakoids of S. veneta did not contain PsbQ protein and its mRNA was absent. When compared to spinach, PsbP was partly depleted (30 %), as was its mRNA. All other thylakoid subunits were present in similar amounts in both species. PSII electron transfer was not affected. Fluorescence was strongly quenched upon irradiation of plants with high light, and relaxed only after prolonged dark incubation. Quenching of fluorescence was not linked to degradation of D1 protein. † Conclusions In S. veneta the PsbQ protein is not necessary for photosynthesis in vivo. As the amount of PsbP is sub-stoichiometric with other PSII subunits, this protein too is largely dispensable from a catalytic standpoint. One possibility is that PsbP acts as an assembly factor for PSII.

We studied the charge recombination characteristics of Photosystem II (PSII) redox components in whole cells of the chlorophyll (Chl) d-dominated cyanobacterium, Acaryochloris marina, by flash-induced chlorophyll fluorescence and thermoluminescence measurements. Flash-induced chlorophyll fluorescence decay was retarded in the mus and ms time ranges and accelerated in the s time range in Acaryochloris marina relative to that in the Chl a-containing cyanobacterium, Synechocystis PCC 6803. In the presence of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea, which blocks the Q(B) site, the relaxation of fluorescence decay arising from S(2)Q(A)(-) recombination was somewhat faster in Acaryochloris marina than in Synechocystis PCC 6803. Thermoluminescence intensity of the so called B band, arising from the recombination of the S(2)Q(B)(-) charge separated state, was enhanced significantly (2.5 fold) on the basis of equal amounts of PSII in Acaryochloris marina as compared with Synechocystis 6803. Our data show that the energetics of charge recombination is modified in Acaryochloris marina leading to a approximately 15 meV decrease of the free energy gap between the Q(A) and Q(B) acceptors. In addition, the total free energy gap between the ground state and the excited state of the reaction center chlorophyll is at least approximately 25-30 meV smaller in Acaryochloris marina, suggesting that the primary donor species cannot consist entirely of Chl a in Acaryochloris marina, and there is a contribution from Chl d as well.

The role of nitric oxide (NO) in photosynthesis is poorly understood as indicated by a number of studies in this field with often conflicting results. As various NO donors may be the primary source of discrepancies, the aim of this study was to apply a set of NO donors and its scavengers, and examine the effect of exogenous NO on photosynthetic electron transport in vivo as determined by chlorophyll fluorescence of pea (Pisum sativum) leaves. Sodium nitroprusside-induced changes were shown to be mediated partly by cyanide, and S-nitroso-N-acetylpenicillinamine provided low yields of NO. However, the effects of S-nitrosoglutathione are inferred exclusively by NO, which made it an ideal choice for this study. Q(A)(-) reoxidation kinetics show that NO slows down electron transfer between Q(A) and Q(B), and inhibits charge recombination reactions of Q(A)(-) with the S(2) state of the water-oxidizing complex in photosystem II. Consistent with these results, chlorophyll fluorescence induction suggests that NO also inhibits steady-state photochemical and nonphotochemical quenching processes. NO also appears to modulate reaction-center-associated nonphotochemical quenching.

To investigate the physiological role of cytochrome b-559 (Cyt b-559) we have constructed a PsbE-H23C mutant of C. reinhardtii in which the His-ligand to the haem provided by the the α subunit has been replaced by Cys. The mutant assembles PSII at reduced levels. To investigate the co-ordination of a haem group by the protein, H23C mutants were generated in a cytochrome b 6 f-less (Cyt b 6 f) background. Analysis by absorbance spectroscopy of pure thylakoids confirmed the lack of a haem group in vivo. Reduction of QB is impaired in the mutant. The mutant is also more sensitive to photoinhibition (PI) than WT cells. Under conditions when the Mn cluster is being photoactivated H23C cells are also more susceptible to PI than WT. Our results indicate that Cyt b-559 plays a role in PSII electron transfer, PSII photoprotection and PSII repair.

The D1 Subunit Of The Photosystem Ii Reaction Center Is Encoded By Three Psba Genes In Thermosynechococcus Elongatus, Which Code For Three Different Protein Forms. We Used Quantitative Rt Pcr To Follow Changes In The Mrna Level Of These Genes, In Combination With Thermoluminescence And Chlorophyll Fluorescence Measurements To Detect Changes In The Electron Transport Activity Of Photosystem Ii Under Exposure To Different Light Conditions. In Cells Adapted To Growth Light Conditions, Psba Transcripts Are Dominated By Psba1. Upon Exposure Of The Cells To High Light Intensity Psba3 Is Replacing Psba1 As The Dominating Psba Mrna Species. Thermoluminescence And Chlorophyll Fluorescence Measurements Indicated Accelerated S2Qa - Charge Recombination When The Main Transcript Species Was Psba3 As Compared To That Of Psba1. These Data Indicate That Changes In The Composition Of The Psba Transcript Pool Lead To Changes In The Distribution Of The Corresponding D1:1 And D1:2 Forms That Result In Different Electron Transport Properties Of Psii.

Increase And Subsequent Decay Of Flash-Induced Chlorophyll Fluorescence Provides A Useful Tool In Psii Electron Transport Studies In A Wide Range Of Experimental Objects Ranging From Isolated Psii Core Complexes To Cyanobacterial Or Algal Cells And Intact Leaves. Typically, Increased Fluorescence Yield Reached Upon Excitation By A Saturating Light Pulse Decreases Monotonically In Time From Its Maximal Level To Fo. This Behaviour Can Be Explained By Assuming The Well-Known Two-Electron Gate Model Of The Psii Acceptor Side. Intact Cells Of The Thermophilic Cyanobacterium Thermosynechococcus Elongatus Do Not Show The Monotonically Decreasing Yield Of Flash-Induced Fluorescence Decay. Instead The Relaxation Curves Possess A Transient Drop With A Minimum Around 100 Ms After The Flash, Followed By An Overshoot After Few Seconds, Resulting In Dampened Oscillation Of The Fluorescence Yield. This Interesting Phenomenon Was Investigated Utilizing Different Acceptors And/Or Inhibitors Of Electron Transport As Well As Temperature-Dependence And Light/Dark Adaptation Conditions. Possible Mechanisms Behind The Oscillating Yield Of Flash-Induced Fluorescence Decay In Intact Cells Of Thermosynechococcus Elongatus Are Discussed.

Storage of thylakoids for several months at 203 K in the dark changes the flash pattern of oxygen evolution by gradually shifting the first oxygen maximum from the third flash, where it is usually observed, to the fourth flash. This effect is accompanied with the increase of a fast phase (t12 = 1.5 s) in the decay of the S2 and S3 states of the water-oxidizing complex in Photosystem II. In parallel to the changes in the oxygen flash pattern the EPR signal from the stable tyrosine-D+ radical (Signal IIslow) completely disappears with a half-time of approx. 13 weeks. The normal oxygen yield sequence, showing the first maximum at the third flash, as well as the original amplitude of Signal IIslow can be restored by a single flash or by continuous illumination at room temperature. These data show that tyrosine-D+ is reduced by an endogenous redox component in Photosystem II during dark storage of thylakoids at 203 K. In parallel with the reduction of tyrosine-D+ we observed the oxidation of high potential cytochrome b-559, and it is proposed that at low temperature an electron can be transferred from high-potential cytochrome b-559 to tyrosine-D+ in a slow reaction in most of the centers.

The decay kinetics for the S2 and S3 states of the water-oxidizing complex have been measured with an unmodulated Joliot-type oxygen electrode in isolated spinach thylakoids. The S2 and S3 states decay biphasically (Vermaas, W.F.J., Renger, G. and Dohnt, G. (1985) Biochim. Biophys. Acta 764, 194–202) with half-decay times of 1–1.5 s and 30–35 s at room temperature. The proportion of the fast phase is negligible in preilluminated thylakoids but increases during dark adaptation to 22–24% for both S2 and S3. This process, t 1 2 ≈ 10 min , is accompanied with the conversion of the S0 state to S1 in about 25% of the centers. Chemical reduction of tyrosine-D+, which gives rise to the EPR Signals IIslow, by dichlorphenolindophenol/ascorbate increases the proportion of the fast decaying phase of S2 and S3 to about 70–80%. The decay of S2 is accompanied by the accumulation of S1 and the decay of S3 results in a transient increase of S2. These data led us to conclude that the fast phase in the S2 and S3 decay is correlated with one-electron donation from tyrosine-D to the water-oxidizing complex located within the same center. This process results in the S3D → S2D+ (→ S1D+) and S2D → S1D+ univalent sequences of deactivating reactions. The electron transfer from tyrosine-D to the S2 and S3 states is strongly temperature-dependent and shows 0.46 and 0.49 eV activation energy, respectively, over the +8 to +37°C temperature range. The deactivation process which is reflected by the slower phase of S2 and S3 decay has an activation energy of 0.65 and 0.76 eV, respectively. An extension of the Kok model of oxygen evolution is also presented taking into account the effect of fast electron donation from tyrosine-D to the water-oxidizing complex.

In Thermosynechococcus elongatus BP-1 , which is the preferred organism in recent structural studies of PSII, three psbA and two psbD genes code for three D1 and one D2 protein isoforms, respectively. The regulation and function of these genes and protein products is largely unknown. Therefore, we used quantitative RT-PCR to follow changes in the mRNA level of the respective genes, in combination with biophysical measurements to detect changes in the electron transport activity of Photosystem II under exposure to different visible and UV light, and temperature conditions. In cells which are acclimated to 40 μmol m − 2 s − 1 growth light conditions at 40 °C the main populations of the psbA and psbD transcripts arise from the psbA1 and psbD1 genes, respectively. When the temperature is raised to 60 °C psbA1 becomes the single dominating psbA mRNA species. Upon exposure of the cells to 500 μmol m − 2 s − 1 intensity visible light psbA3 replaces psbA1 as the dominating psbA mRNA species, and psbD2 increases at the expense of psbD1 . UV-B radiation also increases the abundance of psbA3 , and psbD2 at the expense of psbA1 and psbD1 , respectively. From the different extent of total D1 protein loss in the absence and presence of lincomycin it was estimated that the PsbA3 protein isoform replaces PsbA1 in about 65% of PSII centers after 2 h of high light acclimation. Under the conditions of different psbA transcript distributions chlorophyll fluorescence and thermoluminescence measurements were applied to monitor charge recombination characteristics of the S 2 Q A − and S 2 Q B − states. We obtained faster decay of flash-induced chlorophyll fluorescence in the presence of DCMU, as well as lower peak temperature of the Q and B thermoluminescence bands when PsbA3 replaced PsbA1 as the main D1 protein isoform. The relevance of dynamic changes in the abundance of psbA and psbD transcript levels, as well as D1 protein isoforms in the acclimation of T. elongatus to changing environmental conditions is discussed.

The His332 residue of the D1 protein has been identified as the likely ligand of the catalytic Mn ions in the water oxidizing complex (Ferreira, K.N., Iverson, T.M., Maghlaoui, K., Barber, J.Iwata, S. (2004) Science 303, 1831-1838). However, its function has not been fully clarified. Here we used thermoluminescence and flash-induced chlorophyll fluorescence measurements to characterize the effect of the D1-H333E, D1-H332D and D1-H332S mutations on the electron transport of Photosystem II in intact cells of the cyanobacterium Synechocystis 6803. Although the mutants are not photoautotrophic they all show flash-induced thermoluminescence and chlorophyll fluorescence, which originate from the S(2)Q(A) (-) and S(2)Q(B) (-) recombinations demonstrating that charge stabilization takes place in the water oxidizing complex. However, the conversion of S(2) to higher S states is inhibited and the energetic stability of the S(2)Q(A) (-) charge pair is increased by 75, 50 and 7 mV in the D1-H332D, D1-H332E and D1-H332S mutants, respectively. This is most probably caused by a decrease of E(m)(S(2)/S(1)). Concomitantly, the rate of electron donation from Mn to Tyr-Z(b) during the S(1) to S(2) transition is slowed down, relative to the wild type, 350- and 60-fold in the D1-H332E and D1-H332D mutants, respectively, but remains essentially unaffected in D1-H332S. A further effect of the D1-H332E and D1-H332D mutations is the retardation of the Q(A) to Q(B) electron transfer step as an indirect consequence of the donor side modification. Our data show that although the His residue in the D1-332 position can be substituted by other metal binding residues for binding photo-oxidisable Mn it is required for controlling the functional redox energetics of the Mn cluster.

The D2 polypeptide of the photosystem II (PSII) complex in the green algaChlamydomonas reinhardtii is thought to be reversibly phosphorylated. By analogy to higher plants, the phosphorylation site is likely to be at residue threonine-2 (Thr-2). We have investigated the role of D2 phosphorylation by constructing two mutants in which residue Thr-2 has been replaced by either alanine or serine. Both mutants grew photoautotrophically at wild-type rates, and noninvasive biophysical measurements, including the decay of chlorophyll fluorescence, the peak temperature of thermoluminescence bands, and rates of oxygen evolution, indicate little perturbation to electron transfer through the PSII complex. The susceptibility of mutant PSII to photoinactivation as measured by the light-induced loss of PSII activity in whole cells in the presence of the protein-synthesis inhibitors chloramphenicol or lincomycin was similar to that of wild type. These results indicate that phosphorylation at Thr-2 is not required for PSII function or for protection from photoinactivation. In control experiments the phosphorylation of D2 in wild-type C. reinhardtii was examined by 32P labeling in vivo and in vitro. No evidence for the phosphorylation of D2 in the wild type could be obtained. [14C]Acetate-labeling experiments in the presence of an inhibitor of cytoplasmic protein synthesis also failed to identify phosphorylated (D2.1) and nonphosphorylated (D2.2) forms of D2 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our results suggest that the existence of D2 phosphorylation in C. reinhardtii is still in question.

Molecular oxygen - essential for all living organisms — is produced by the photosynthetic oxidation of water in photosystem II (PSII) of higher plants, algae and cyanobacteria. The water-oxidizing complex of PSII contains a cluster of 4 Mn atoms, and turns over through five different redox states, denoted by S0-S4, during its function.

The source of molecular oxygen on Earth is the oxidation of water by Photosystem II in oxygenic photosynthesis. The water oxidising complex is composed of a Mn-cluster ligated to a protein environment and Cl- and Ca2+ ions. During water oxidation the Mn-cluster cycles through five different oxidation states (S0-S4).

Two missense mutants, A263P and S264P, and a deletion mutant des-Ala263, Ser264, have been constructed in the D1 protein of the cyanobacterium Synechocystis sp PCC 6803. All were expected to induce a significant conformational change in the QB-binding region of photosystem II (PSII). Although the des-Ala263, Ser264-D1 mutant accumulated some D1 protein in the thylakoid membrane it was unable to grow photoautotrophically or evolve oxygen. Thermoluminescence and chlorophyll fluorescence studies confirmed that this deletion mutant did not show any functional PSII activity. In contrast, [S264P]D1 was able to grow photoautotrophically and give light-saturated rates of oxygen evolution at 60% of the rate of the wild-type control strain, TC31. The A263P missense mutant was also able to evolve oxygen at 50% of TC31 rates although it did not readily grow photoautotrophically. Thermoluminescence, flash oxygen yield and chlorophyll fluorescence measurements indicated that in both missense mutants electron transfer from QA to QB was significantly impaired in dark adapted cells. However, QA to QB electron transfer could be photoactivated in the mutants by background illumination. Both the A263P and S264P mutants also showed an increase in resistance to the s-triazine family of herbicides although this feature did not hold for the phenolic herbicide, ioxynil. Of particular interest was that the two missense mutants, especially S264P, possessed a slower rate of turnover of the D1 protein compared with TC31 and in vivo contained detectable levels of a 41-kDa adduct consisting of D1 and the alpha subunit of cytochrome b559. When protein synthesis was blocked by the addition of lincomycin, D1 degradation was again slower in S264P than TC31. The results are discussed in terms of structural changes in the QB-binding region which affect herbicide and plastoquinone binding and perturb the normal regulatory factors that control the degradation of the D1 protein and its synchronisation with the synthesis of a replacement D1 protein.

Current structural models indicate that the D1 and D2 polypeptides of the Photosystem two reaction center complex (PS II RC) each span the thylakoid membrane five times. In order to assess the importance of the lumenal extrinsic loop that connects transmembrane helices I and II of D1 we have constructed five deletion mutants and two double mutants in the cyanobaterium Synechocystic sp. PCC 6803. Four of the deletion mutants (Δ59-65, Δ69-74, Δ79-86 and Δ109-110) are obligate photoheterotrophs unable to accumulate D1 in the membrane as assayed by immunoblotting experiments or pulse-labelling experiments using [(35)S]-methionine. In contrast deletion mutant Δ100 which lacks A100 behaved very similarly to the WT control strain in terms of photoautotrophic growth rate, saturated rates of oxygen evolution, flash-induced oxygen evolution, fluorescence induction and decay, and thermoluminescence. Δ100 is the first example of an internal deletion on the lumenal side of the D1 polypeptide that is benign to photosystem two function. Double mutant D103G/E104A also behaves similarly to the WT control strain leading to the conclusion that residues D103 and E104 are unlikely to be involved in ligating the metal ions Mn or Ca(2+), which are needed for photosynthetic oxygen evolution. Double mutant, G109A/G110A, was constructed to assess the significance of this GlyGly motif which is also conserved in the L subunit of purple bacterial reaction centres. The G109A/G110A mutant is able to evolve oxygen at approximately 50-70% of WT rates but is unable to grow phatoautotrophically apparently because of an enhanced sensitivity to photoinactivation than the WT control strain. A photoautotropic revertant was isolated from this strain and shown to result from a mutation that restored the WT codon at position 109. Pulse-chase experiments in cells using [(35)S]-methionine showed that resistance to photoinhibition in the revertant correlated with an enhanced rate of incorporation of D1 into the membrane compared to mutant G109A/G110A. The sensitivity to photoinhibition shown by the G109A/G110A mutant is therefore consistent with a perturbation to the D1 repair cycle possibly at the level of D1 synthesis or incorporation of D1 into the PS II complex.

Photosynthetic oxidation of water to molecular oxygen occurs via a four-step reaction sequence that is catalysed by the Mn-containing water-oxidizing complex of photosystem II [1]. The characteristic period-four oscillation of flash-induced oxygen evolution [2] reflects the cycling of the water-oxidizing complex through five redox states denoted S0–S4 [3]. The oxygen molecule is released in the S3 to S0 transition in which S4 is a transient state. In the light S0 to S3 are equally populated but S2 and S3 decays back to S1 when the light is switched off [4]. In the original S-state model both S0 and S1 were assumed to be stable in the dark [3]. The reality of dark stable S0 state was, however, questioned by different authors who proposed that a fast electron donation from D, a PS II donor species, in about 25% of the centers was responsible for the apparent S0 fraction present after long dark adaptation [5–7]. The characteristics and redox state of D, which has recently been identified as tyrosine-160 of D2 protein [8] of PS II reaction center complex, have been studied mainly by measuring EPR Signal IIslow arising from D+ [9]. The quantitative establishment of the effect of D on the distribution and stability of S2 and S3 is expected to provide a new tool to monitor the redox state of D by simple flash-oxygen yield measurements.