Publications (71) View all
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Article: Effect of partial or complete elimination of light-harvesting complexes on the surface electric properties and the functions of cyanobacterial photosynthetic membranes.
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ABSTRACT: Influence of the modification of the cyanobacterial light-harvesting complex [i.e. phycobilisomes (PBS)] on the surface electric properties and the functions of photosynthetic membranes was investigated. We used four PBS mutant strains of Synechocystis sp. PCC6803 as follows: PAL (PBS-less), CK (phycocyanin-less), BE (PSII-PBS-less) and PSI-less/apcE(-) (PSI-less with detached PBS). Modifications of the PBS content lead to changes in the cell morphology and surface electric properties of the thylakoid membranes as well as in their functions, such as photosynthetic oxygen-evolving activity, P700 kinetics and energy transfer between the pigment-protein complexes. Data reveal that the complete elimination of PBS in the PAL mutant causes a slight decrease in the electric dipole moments of the thylakoid membranes, whereas significant perturbations of the surface charges were registered in the membranes without assembled PBS-PSII macrocomplex (BE mutant) or PSI complex (PSI-less mutant). These observations correlate with the detected alterations in the membrane structural organization. Using a polarographic oxygen rate electrode, we showed that the ratio of the fast to the slow oxygen-evolving PSII centers depends on the partial or complete elimination of light-harvesting complexes, as the slow operating PSII centers dominate in the PBS-less mutant and in the mutant with detached PBS.Physiologia Plantarum 05/2012; · 3.11 Impact Factor -
Article: Fast cadmium inhibition of photosynthesis in cyanobacteria in vivo and in vitro studies using perturbed angular correlation of γ-rays
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ABSTRACT: The effect of cadmium on the photosynthetic activity of Synechocystis PCC 6803 was monitored in this study. The oxygen evolving capacity of Synechocystis treated with 40μM CdCl2 was depressed to 10% of the maximum in 15min, indicating that Cd2+ penetrated rapidly into the cells and blocked the photosynthetic activity. However, neither photosystem II (PSII) nor photosystem I (PSI) activity showed a significant short-term decrease which would explain this fast decrease in the whole-chain electron transport. Thermoluminescence measurements have shown that the charge separation and stabilization in PSII remains essentially unchanged during the first few hours following the Cd2+ treatment. The electron flow through PSI was monitored by following the redox changes of the P700 reaction centers of PSI. Alterations in the oxidation kinetics of P700 in the Cd2+-treated cells indicated that Cd2+ treatment might affect the available electron acceptor pool of P700, including the CO2 reduction and accumulation in the cells. Perturbed angular correlation of γ-rays (PAC) using the radioactive 111mCd isotope was used to follow the Cd2+ uptake at a molecular level. The most plausible interpretation of the PAC data is that Cd2+ is taken up by one or more Zn proteins replacing Zn2+ in Synechocystis PCC 6803. Using the radioactive 109Cd isotope, a protein of approximately 30kDa that binds Cd2+ could be observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results indicate that Cd2+ might inactivate different metal-containing enzymes, including carbonic anhydrase, by replacing the zinc ion, which would explain the rapid and almost full inhibition of the photosynthetic activity in cyanobacteria.JBIC Journal of Biological Inorganic Chemistry 04/2012; 11(6):725-734. · 3.29 Impact Factor -
Article: EPR study of thylakoid membrane dynamics in mutants of the carotenoid biosynthesis pathway of Synechocystis sp. PCC6803.
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ABSTRACT: EPR spectroscopy using 5-doxylstearic acid (5-SASL) and 16-doxylstearic acid (16-SASL) spin probes was used to study the fluidity of thylakoid membranes. These were isolated from wild type Synechocystis and from several mutants in genes encoding selected enzymes of the carotenoid biosynthesis pathway and/or acyl-lipid desaturases. Cyanobacteria were cultivated at 25°C and 35°C under different light regimes: photoautotrophically (PAG) and/or in light-activated heterotrophic conditions (LAHG). The relative fluidity of membranes was estimated from EPR spectra based on the empirical outermost splitting parameter in a temperature range from 15°C to 40°C. Our findings demonstrate that in native thylakoid membranes the elimination of xanthophylls decreased fluidity in the inner membrane region under optimal growth conditions (25°C) and increased it under sublethal heat stress (35°C). This indicated that the overall fluidity of native photosynthetic membranes in cyanobacteria may be influenced by the ratio of polar to non-polar carotenoid pools under different environmental conditions.Acta biochimica Polonica 03/2012; 59(1):87-90. · 1.49 Impact Factor -
Article: Two functional sites of phosphatidylglycerol for regulation of reaction of plastoquinone Q(B) in photosystem II.
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ABSTRACT: Functional roles of an anionic lipid phosphatidylglycerol (PG) were studied in pgsA-gene-inactivated and cdsA-gene-inactivated/phycobilisome-less mutant cells of a cyanobacterium Synechocystis sp. PCC 6803, which can grow only in PG-supplemented media. 1) A few days of PG depletion suppressed oxygen evolution of mutant cells supported by p-benzoquinone (BQ). The suppression was recovered slowly in a week after PG re-addition. Measurements of fluorescence yield indicated the enhanced sensitivity of Q(B) to the inactivation by BQ. It is assumed that the loss of low-affinity PG (PG(L)) enhances the affinity for BQ that inactivates Q(B). 2) Oxygen evolution without BQ, supported by the endogenous electron acceptors, was slowly suppressed due to the direct inactivation of Q(B) during 10 days of PG depletion, and was recovered rapidly within 10h upon the PG re-addition. It is concluded that the loss of high-affinity PG (PG(H)) displaces Q(B) directly. 3) Electron microscopy images of PG-depleted cells showed the specific suppression of division of mutant cells, which had developed thylakoid membranes attaching phycobilisomes (PBS). 4) Although the PG-depletion for 14 days decreased the chlorophyll/PBS ratio to about 1/4, flourescence spectra/lifetimes were not modified indicating the flexible energy transfer from PBS to different numbers of PSII. Longer PG-depletion enhanced allophycocyanin fluorescence at 683nm with a long 1.2ns lifetime indicating the suppression of energy transfer from PBS to PSII. 5) Action sites of PG(H), PG(L) and other PG molecules on PSII structure are discussed.Biochimica et Biophysica Acta 02/2012; 1817(2):287-97. · 4.66 Impact Factor -
Chapter: The Role of Membrane Structure in Acclimation to Low-Temperature Stress
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ABSTRACT: All photosynthetic protein complexes are embedded in membranes, and lipids surround these complexes. These lipids are indispensable not only in maintaining the functional state/conformation of the photosynthetic reaction centers, but are also needed for protection against environmental stress conditions such as cold and chilling. The redox enzymes, elements of the photosynthetic electron transport chain, which transform the physical energy of the photons to chemical potential, are also in the photosynthetic complexes. During low-temperature stress conditions, the rate of photosynthetic electron transport decreases. This decrease can be enhanced further by exposing the photosynthetic apparatus to high light-intensities. In this chapter, we concentrate on the role of the photosynthetic membrane, especially on the structural aspects of the lipids involved in the protection against low-temperature stress. Genetic manipulations of higher plants and cyanobacteria have suggested that unsaturation of lipids plays an important role in preserving photosynthetic functions at low temperatures. Lipids, in particular phosphatidylglycerol, the only phospholipid among the components of the photosynthetic membrane, seem to be active partners of the proteins in the adaptive response to low-temperature stress. In addition to lipids, carotenoids, by exerting local effects, may also participate in membrane dynamics-based protective mechanisms. Fourier transform infrared spectroscopy has proven to be a valuable tool to reveal protein secondary structure/dynamics, and lipid conformation. Since in the infrared spectrum the regions characteristic mostly for proteins or lipids are well separated, infrared spectroscopy is a method of choice to reveal structural and dynamic changes, as well as lipid-protein interactions in the photosynthetic membranes during low-temperature stress conditions.12/2011: pages 233-250;
