Nitrogen is an essential factor for normal plant and algal development. As a component of nucleic acids, proteins, and chlorophyll (Chl) molecules, it has a crucial role in the organization of a functioning photosynthetic apparatus. Our aim was to study the effects of nitrogen starvation in cultures of the unicellular green alga, Chlamydomonas reinhardtii, maintained on nitrogen-free, and then on nitrogen-containing medium. During the three-week-long degreening process, considerable changes were observed in the Chl content, the ratio of Chl-protein complexes, and photosynthetic activity of the cultures as well as in the ultrastructure of single chloroplasts. The regreening process was much faster then the degradation; total greening of the cells occurred within four days. The rate of regeneration depended on the nitrogen content. At least 50% of the normal nitrogen content of Tris-Acetate-Phosphate (TAP) medium was required in the medium for the complete regreening of the cells and regeneration of chloroplasts., É. Preininger, A. Kósa, Z. S. Lőrincz, P. Nyitrai, J. Simon, B. Böddi, Á. Keresztes, I. Gyurján., and Obsahuje seznam literatury
The specific features of the structural and functional organisation of the photosynthetic apparatus (PSA) were studied in wild halophytes representing three strategies of salt tolerance: euhalophyte Salicornia perennans, crynohalophyte Limonium gmelinii, and glycohalophyte Artemisia santonica. The sodium content in aboveground parts of the plants corresponded to the strategy of salt tolerance. The photosynthetic cells of the euhalophyte were large and contained a higher number of chloroplasts than those in other species. In contrast, the number of cells per a leaf area unit was lower in S. perennans as compared to cryno- and glycohalophytes. Thereupon, the cell and chloroplast surface area per leaf area unit declined in the following sequence: A. santonica > L. gmelinii > S. perennans. However, the large cells of euhalophyte contained chloroplasts of larger sizes with 4- to 5-fold higher chlorophyll (Chl) content per chloroplast and Chl concentration in chloroplast volume unit. Also, chloroplasts of S. perennans were characterised by the higher content of glyco- and phospholipids. Qualitative composition of fatty acids (FA) in lipids isolated from the chloroplast-enriched fraction was similar in all three species; however, the index of unsaturation of FA was higher in glycohalophyte A. santonica than those in two other species. Under natural condition, PSA of all three halophytes showed high resistance to soil salinity. The results indicated tolerance of PSII to the photodamage in halophytes. The high rate of electron transport through PSII can be important to prevent oxidative damage of PSA in halophytes under strong light and hight temperature in vivo. Thus, the strategy of salt tolerance is provided by both the leaf anatomical structure and the ultrastructure of photosynthetic membranes, which is determined in particular by the specific composition of lipids., O. A. Rozentsvet, E. S. Bogdanova, L. A. Ivanova, L. A. Ivanov, G. N. Tabalenkova, I. G. Zakhozhiy, V. N. Nesterov., and Seznam literatury
The irregular distribution of stress in rock mass is a decisive factor for the origin of rock bursts. Besides, a sound knowledge of stress distribution is very important in the excavation of mine workings. Stress state is affected both by natural stress, including the gravitational, tectonic, hydraulic and residual stress and the stress induced by mining operations. Natural stress fields are defined by their geological structure and rock properties. It is important in mining practice to understand that there is a close relationship between recent and residual tectonic stress, as defined by tectonic evolution and tectonic structure. Since 1994, a large number of horizontal stress measurements have been carried out at a depth of 600 m to 800 m under the surface. The application of the results obtained from the measurements of stress and their comparison with the results of structural analysis and their generalization for the Karviná subbasin can be an important contribution to optimize the timespace designs of the mining activity., Petr Waclawik, Jiří Ptáček and Radomír Grygar., and Obsahuje bibliografii
Preferential flow paths in the crust, as caused by the presence of the Luchlompolo fault in the drilled section of the Kola Superdeep Borehole (SG-3) and the dip angle of the rock structural elements (layering, schistosity, banding), are favourable for migration of deep fluids to the Earth’s surface. An investigation of the structure, anisotropy and permeability of rocks under PT-conditions in the SG-3 section, in addition to the occurrence of He-isotopes, reveals that the high-permeability zones of the exposed crustal segment are related to two important structural elements of the section: in the upper zone - to the Luchlompolo fault, in the lower one to the contact between the Proterozoic and Archaean complexes. The obtained results on the rock samples from SG-3 indicate a rough correlation between permeability and elastic anisotropy of various rock samples. Simulating increased PT-conditions, corresponding to the relevant depths of 6-8 km document the overlapping temperature and pressure effect, i.e. resulting in a sharp decrease of rock permeability., Felix F. Gorbatsevich, Serafim V. Ikorsky and Andrey V. Zharikov., and Obsahuje bibliografii
The oxidizing side of photosystem 2 (PS2) contains a set of unique redox components including two tyrosine radicals, Tyr2 and Tyrp, and a cluster of 4 Mn atoms that are involved in the oxidation of water to molecular oxygen. The structural environment of these components is unknown; we ušed computer-assisted modelling to create a three-dimensional model for the structure around Tyr^ and Tyrj). The tyrosines are predicted to be located in hydrophobic cavities in the Dl and D2 reaction centre proteins, respectively. The cavities are situated close to the lumenal surface of the thylakoid membrane and are surrounded mainly by highly conserved amino acid residues. Both tyrosines are proposed to be hydrogen-bonded to the nearby histidine residues Hisl90 on respective protein. We tested the model by electron paramagnetic resonance (EPR) spectroscopy of Tyr^ and site-directed mutagenesis of the D2 protein in the cyanobacterium Synechocystis 6803. In two mutants, where the corresponding histidine is changed to a tyrosine or a leucine, the normál EPR spectra from Tyr^ were drastically altered to narrow structureless radical signals with g-values similar to that of Tyrp (g » 2.0050). The new spectra were assigned to Tyrp from functional experiments and the spectral modification indicated that the introduced point-mutation of His 190 (D2-Hisl89 in Synechocystis 6803) modified the environment around Tyr^ supporting the structural model. In a third mutant where Glnl65 (D2-Glnl64 in Synechocystis 6803) was exchanged to a leucine we also observed a modified EPR spectrum consistent with the predictions firom the model. AU the experimental data obtained strengthen the Computer derived model in essential aspects. We also predicted a possible location for the Mn-cluster to the loop that connects the membrane spanning helices A and B on the Dl protein. In addition the structural model suggests the presence of a metal-site, possibly a Mn site, close to Tyrz on the Dl protein. The site is proposed to be constituted of three residues on the Dl protein, Glnl65, Aspl70 and Glul89.
Phoridae (scuttle flies) are widely distributed, occur in many types of habitats and are ecologically versatile, which makes them an excellent bioindicator group for evaluating faunal diversity. The structure of scuttle fly communities was compared in two Mediterranean habitats in the Montseny Natural Park (Catalonia, Spain) that differ in vegetation and microclimate: beech forest and highland scrubland. 3684 male individuals belonging to 135 species of scuttle flies were identified. Scuttle flies were more abundant in beech forest than scrubland. Observed and estimated species richness were lower in scrubland than in beech forest, while diversity was similar in both habitats. Community evenness was greater in scrubland than beech forest. Therefore, the percentage of dominant and subdominant species was higher in scrubland than beech forest, while the percentage of rare species was higher in beech forest than scrubland. Scuttle fly species composition was significantly different in the two habitats, but it was similar among plots within the same habitat. Megaselia pectoralis (Wood, 1910) and Megaselia subpleuralis (Wood, 1909) were the dominant species in beech forest, while Megaselia pusilla (Meigen, 1830), Megaselia pumila (Meigen, 1830), Megaselia superciliata (Wood, 1910) and Megaselia diversa (Wood, 1909) were the dominant species in scrubland. Trophic specialization was higher in beech forest than scrubland. Saprophages were the dominant trophic group in beech forest, while fungivores and polyphages were dominant in scrubland. The high biodiversity of scuttle flies recorded in the Montseny Natural Park indicates that there is also a high diversity of other taxa there and that these Mediterranean mountains are of high conservation status., Carlos García-Romera, José A. Barrientos., and Obsahuje bibliografii
NMDA receptors have received much attention over the last few decades, due to their role in many types of neural plasticity on the one hand, and their involvement in excitotoxicity on the other hand. There is great interest in developing clinically relevant NMDA receptor antagonists that would block excitotoxic NMDA receptor activation, without interfering with NMDA receptor function needed for normal synaptic transmission and plasticity. This review summarizes current understanding of the structure of NMDA receptors and the mechanisms of NMDA receptor activation and modulation, with special attention given to data describing the properties of various types of NMDA receptor inhibition. Our recent analyses point to certain neurosteroids as NMDA receptor inhibitors with desirable properties. Specifically, these compounds show use-dependent but voltage-independent block, that is predicted to preferentially target excessive tonic NMDA receptor activation. Importantly, neurosteroids are also characterized by use-independent unblock, compatible with minimal disruption of normal synaptic transmission. Thus, neurosteroids are a promising class of NMDA receptor modulators that may lead to the development of neuroprotective drugs with optimal therapeutic profiles., V. Vyklicky ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
Ciel'om článku je priblížiť čitatel'ovi niektoré súčasné predstavy o svetle, ktoré vychádzajú z poznatkov fyziky elementárnych častíc. Je pomerne udivujúce, no málokto si vie predstaviť, že aj fotón môže mať vnútornú štruktúru, ktorá je pre neho špecifická do tej miery, ako je špecifická štruktúra protónu., The goal of this paper is to introduce some current views of the nature of light from the elementary particle physics. Often, it is hard to imagine that the photon has a specific structure as for example a proton has. This paper sheds light on the structure of the photon., Dušan Bruncko., and Obsahuje seznam literatury
Biological membrane mimetics, such as liposomes, lipid bilayers and model membranes, are used in a broad range of scientific and technological applications due to the unique physical properties of these amphiphilic aggregates. They serve as platforms for studying soft matter physics of membranes and membrane dynamics, interactions of bilayers with drugs, and effects of various additives of environmental changes. State-of-the-art research takes advantage of the combination of the brilliance of X-ray scattering sources with peculiar properties of neutrons and the power of computer simulations. The advances in chemistry, and in particular the possibility of deuteration, enables improved experimental spatial resolution and the ability to pi-point labels within membranes. It is only a matter of time for many biological functions, which occur at the membrane interface, to be matched with the structural properties of these membranes., Článok referuje o zákonitostiach stavby lipidových membrán a ich interakciách s biologicky aktívnymi molekulami. Vplyv iónov nachádzajúcich sa v prirodzenom prostredí bunkovej membrány, anestetický efekt alkánov a účinok cholesterolu a melatonínu pri zabudovaní do membrány je diskutovaný najmä z pohľadu zmeny štruktúry lipidovej matrice membrány. Štruktúrne výsledky sú získané pomocou experimentálnych prístupov, pričom dôraz sa kladie na pokrok dosiahnutý v metódach využívajúcich moderné zdroje röntgenového žiarenia a neutrónov., Norbert Kučerka., and Obsahuje bibliografii