Cladocerans as indicators in the importance of passive nature conservation

The aim of our study was to verify the effectiveness of passive nature conservation with regard to the preservation of species, by examining a typical mesozooplankton community. We investigated five oxbow lakes which were similar to each other in terms of size, depth and close-to-each, but which differed markedly from one to another in terms of lake management. One is under passive protection, the others are under different forms of management. Based on the NMDS (Non-metric Dimensional Scaling) analysis, we identified the variable (transparency) which is responsible for the segregation. In the case of rare species IndVal (Indicator Value) analysis was used to evaluate the occurrence and significance of indicator species. We also found marked differences in the species composition; seven species showed indicator values for the protected oxbow lake, five of which were significant (p <?0.001). In contrast, in the case of the other four oxbow lakes, a total of one species showed an indicator value. Finally, regression tree analysis was used to distinguish the oxbow lakes from each other for both common and mass-occurring species. Among the mass-occurring species, the protected oxbow lake is characterized by a large number of Acropreus harpae (Baird, 1835), while in case of the other, non-protected, oxbow lakes Alona guttata (Sars, 1862) and Alonella excisa (Fischer, 1854) are the basis for the separate classification. There is a positive effect of passive protection regarding the quantitative and qualitative occurrence of the zooplankton community. Our study highlights the importance of this kind of passive protection in the life of a particular water body and advocates that their protection should be maintained.     

Purification, crystallization and X-ray diffraction analyses of the T. elongatus PSII core dimer with strontium replacing calcium in the oxygen-evolving complex

The core complex of photosystem II (PSII) was purified from thermophilic cyanobacterium Thermosynechococcus elongatus grown in Sr(2+)-containing and Ca(2+)-free medium. Functional in vivo incorporation of Sr(2+) into the oxygen-evolving complex (OEC) was confirmed by EPR analysis of the isolated and highly purified SrPSII complex in agreement with the previous study of Boussac et al. [J. Biol. Chem. 279 (2004) 22809-22819]. Three-dimensional crystals of SrPSII complex were obtained which diffracted to 3.9 A and belonged to the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions of a=133.6 A, b=236.6 A, c=307.8 A. Anomalous diffraction data collected at the Sr K-X-ray absorption edge identified a novel Sr(2+)-binding site which, within the resolution of these data (6.5 A), is consistent with the positioning of Ca(2+) in the recent crystallographic models of PSII [Ferreira et al. Science 303 (2004) 1831-1838, Loll et al. Nature 438 (2005) 1040-1044]. Fluorescence measurements on SrPSII crystals confirmed that crystallized SrPSII was active in transferring electrons from the OEC to the acceptor site of the reaction centre. However, SrPSII showed altered functional properties of its modified OEC in comparison with that of the CaPSII counterpart: slowdown of the Q(A)-to-Q(B) electron transfer and stabilized S(2)Q(A)(-) charge recombination.     

The sensitivity of Photosystem II to damage by UV-B radiation depends on the oxidation state of the water-splitting complex

The water-oxidizing complex of Photosystem II is an important target of ultraviolet-B (280-320 nm) radiation, but the mechanistic background of the UV-B induced damage is not well understood. Here we studied the UV-B sensitivity of Photosystem II in different oxidation states, called S-states of the water-oxidizing complex. Photosystem II centers of isolated spinach thylakoids were synchronized to different distributions of the S(0), S(1), S(2) and S(3) states by using packages of visible light flashes and were exposed to UV-B flashes from an excimer laser (lambda=308 nm). The loss of oxygen evolving activity showed that the extent of UV-B damage is S-state-dependent. Analysis of the data obtained from different synchronizing flash protocols indicated that the UV-sensitivity of Photosystem II is significantly higher in the S(3) and S(2) states than in the S(1) and S(0) states. The data are discussed in terms of a model where UV-B-induced inhibition of water oxidation is caused either by direct absorption within the catalytic manganese cluster or by damaging intermediates of the water oxidation process.     

Metastability of microtubules induced by competing internal forces

Recent modeling efforts to estimate energies of tubulin-tubulin bonds shed light on a delicate balance between competing mechanical forces maintaining microtubule walls. Here we formulate two important refinements to the explanation of bond energetics. First, energy surface calculations in the elastic filament approximation reveal a finite stabilizing barrier assumed a simple Lennard-Jones-like potential for protein bonds. The presence of a guanosine triphosphate (GTP) cap represented by straight segments is necessary, as it is predicted for a long time. In the lack of such a cap, the protofilaments are either in an absolutely stable or absolutely unstable state. Second, our calculations show that this barrier appears only if the mechanical energy associated with the conformational change after GTP hydrolysis (curling energy) is larger than the strength of lateral bonds. The overall energy balance we propose supports continuous assembly of GTP dimers, a metastable state in the presence of a finite GTP cap and energetically driven disassembly of guanosine diphosphate protofilaments.     

Effects of pectin-induced passive linkage of gastric H on the gastric acid secretion and on the development of ethanol- and salicylate-induced gastric mucosal lesions in rats

The aim of this study was to evaluate the effects of intragastrically given pectin-induced physicochemical properties and actions on active gastric acid secretion and on the development of ethanol- and aspirin-induced gastric mucosal lesions. The observations were carried out on CFY-strain rats, fasted for 24 h before the experiments with water ad libitum. The observations were carried out in two experimental series. A) The gastric mucosal lesions were produced by intragastrically given 96% ethanol or aspirin prepared with 0.2 M HCl. Different doses of pectin (100, 50 and 25 mg.kg^–1, respectively) were administered intragastrically 30 min before giving necrotizing agents. The number of gastric lesions was noted 1 h after the administration, while the severity of gastric mucosal lesions was scored by semi-quantitative scale. B) The effects of pectin were studied on the volume and H⁺ secretion of the stomach in 4-h pylorus-ligated rats. It has been found that: 1) the gastric mucosal lesions could be produced in 100% of rats by the application of both necrotizing agents. 2) Pectin in doses of 50–100 mg.kg^–1 increased the number of gastric mucosal lesions in both models, while no increase was produced by the application of 25-mg.kg^–1 dose. 3) The severity of mucosal lesions increased significantly after the administration of all doses of pectin. 4) The pectin-induced increase of gastric lesions (number) showed a dose-response effect. 5) The pectin produced a significant increase in the volume of gastric secretion and gastric H⁺ secretion. It has been concluded that: a) pectin-induced physicochemical changes are able to enhance the aggression to gastric mucosa produced by ethanol and aspirin; b) a positive correlation exists between the linkage of H⁺ to pectin and significant active metabolic response in the rat stomach; c) pectin alone stimulates the active metabolic process of the gastric H⁺ secretion.     

T-DNA-mediated transfer of Agrobacterium tumefaciens chromosomal DNA into plants

Besides the well-documented integration of DNA flanked by the transfer DNA borders, occasional insertion of fragments from the tumor-inducing plasmid into plant genomes has also been reported during Agrobacterium tumefaciens-mediated transformation. We demonstrate that large (up to approximately 18 kb) gene-bearing fragments of Agrobacterium chromosomal DNA (AchrDNA) can be integrated into Arabidopsis thaliana genomic DNA during transformation. One in every 250 transgenic plants may carry AchrDNA fragments. This has implications for horizontal gene transfer and indicates a need for greater scrutiny of transgenic plants for undesired bacterial DNA.     

Interaction of Cu(II)with His-Val-Gly-Asp and of Zn(II) with His-Val-His,Two Peptides at the Active Site of Cu,Zn-Superoxide Dismutase

His-Val-His and His-Val-Gly-Asp are two naturally occurring peptide sequences, present at the active site of Cu,Zn-superoxide dismutase (Cu,Zn-SOD). We have already studied the interaction of His-Val-His=A (copper binding site) with Cu(II) and of His-Val-Gly-Asp=B (zinc binding site) with Zn(II). As a continuation of this work and for comparison purposes we have also studied the interaction of Zn(II) with His-Val-His and Cu(II) with His-Val-Gly-Asp using both potentiometric and spectroscopic methods (visible, EPR, NMR). The stoichiometry, stability constants and solution structure of the complexes formed have been determined. Histamine type of coordination is observed for/ZnAH/²⁺, /ZnA/⁺, /ZnA²H/⁺ and/ZnA²/ in acidic pH while deprotonation of coordinated water molecules is observed at higher pH. /CUB/ species is characterized by the formation of a macrochelate and histamine type coordination. Its stability results in the suppression of amide deprotonation which occurs at high pH resulting in the formation of the highly distorted from square planar geometry 4N complex/CuBH_-3/³.     

Glyphosate complexation to aluminium(III). An equilibrium and structural study in solution using potentiometry, multinuclear NMR, ATR-FTIR, ESI-MS and DFT calculations

The stoichiometries and stability constants of a series of Al³⁺-N-phosponomethyl glycine (PMG/H₃L) complexes have been determined in acidic aqueous solution using a combination of precise potentiometric titration data, quantitative ²⁷Al and ³¹P NMR spectra, ATR-FTIR spectrum and ESI-MS measurements (0.6 M NaCl, 25 °C). Besides the mononuclear AlH₂L²⁺, Al(H₂L)(HL), and Al(HL)L²⁻, dimeric Al₂(HL)L⁺ and trinuclear complexes have been postulated.¹H and ³¹P NMR data show that different isomers co-exist in solution and the isomerization reactions are slow on the ³¹P NMR time scale. The geometries of monomeric and dimeric complexes likely double hydroxo bridged and double phosphonate bridged isomers have been optimized using DFT ab initio calculations starting from rational structural proposals. Energy calculations using the PCM solvation method also support the co-existence of isomers in solutions.     

Thermoluminescence: experimental

Thermoluminesence measurements are useful for the study of Photosystem II electron transport in intact leaves, in algal and cyanobacterial cells, as well as in isolated membrane complexes. Here an overview of the experimental approaches is provided. In the present review, instruments and the experimental procedures for measuring thermoluminescence emission from photosynthetic systems of various origins are summarized and discussed. Major pitfalls frequently encountered in measurements with isolated membranes, suspensions of intact organisms or solid leaf samples are highlighted. Analytical and numeric methods for the analysis of measured thermoluminescence curves are also discussed.