Effects of light intensity and temperature on the photosynthetic irradiance response curves and chlorophyll fluorescence in three picocyanobacterial strains of Synechococcus

Chrococcoid cyanobacteria of the genus Synechococcus are the important component of marine and freshwater ecosystems. Picocyanobacteria comprise even 80% of total cyanobacterial biomass and contribute to 50% of total primary cyanobacterial bloom production. Chlorophyll (Chl) fluorescence and photosynthetic light response (P-I) curves are commonly used to characterize photoacclimation of Synechococcus strains. Three brackish, picocyanobacterial strains of Synechococcus (BA-132, BA-124, BA-120) were studied. They were grown under 4 irradiances [10, 55, 100, and 145 μmol(photon) m^?2 s^?1] and at 3 temperatures (15, 22.5, and 30°C). Photosynthetic rate was measured by Clark oxygen electrode, whereas the Chl fluorescence was measured using Pulse Amplitude Modulation fluorometer. Based on P-I, two mechanisms of photoacclimation were recognized in Synechococcus. The maximum value of maximum rate of photosynthesis (P _max) expressed per biomass unit at 10 μmol(photon) m^?2 s^?1 indicated a change in the number of photosynthetic units (PSU). The constant values of initial slope of photosynthetic light response curve (α) and the maximum value of P _max expressed per Chl unit at 145 μmol(photon) m^?2 s^?1 indicated another mechanism, i.e. a change in PSU size. These two mechanisms caused changes in photosynthetic rate and its parameters (compensation point, α, saturation irradiance, dark respiration, P _max) upon the influence of different irradiance and temperature. High irradiance had a negative effect on fluorescence parameters, such as the maximum quantum yield and effective quantum yield of PSII photochemistry (φ_PSII), but it was higher in case of φ_PSII.     

Facies development and sequence stratigraphy of the Ludfordian (Upper Silurian) deposits in the Zbruch River Valley, Podolia, western Ukraine: local facies overprint on the δ13Ccarb record of a global stable carbon isotope excursion

The Ludfordian (Upper Silurian) succession in Podolia, western Ukraine, represents a Silurian carbonate platform developed in an epicontinental sea on the shelf of the paleocontinent of Baltica. Coeval deposits throughout this basin record a positive stable carbon isotope excursion known as the Lau excursion. The record of this excursion in Podolia exhibits an unusual amplitude from highly positive (+6.9 ‰) to highly negative (?5.0 ‰) δ¹³C_carb values. In order to link δ¹³C_carb development with facies, five sections in the Zbruch River Valley were examined, providing microfacies characterization and revised definitions of the Isakivtsy, Prygorodok, and Varnytsya Formations. The Isakivtsy Fm. is developed as dolosparite replacing originally bioclastic limestone. The Prygorodok Fm., recording strongly depleted (down to ?10.53 ‰) to near zero (0.12 ‰) δ¹³C_carb values is developed as laminated, organic-rich dolomicrite with metabentonite and quartz siltstone beds. The Varnytsya Fm. is characterized by peritidal deposition with consistent, slightly negative δ¹³C_carb values (?0.57 to ?3.20 ‰). It is proposed that dolomitization of the Isakivtsy Fm. is associated with a sequence boundary and erosional surface. The overlying Prygorodok Fm. represents the proximal part of a TST deposited in restricted and laterally extremely variable environments dominated by microbial carbonate production. The transition to the overlying Varnytsya Fm. facies is marked by a maximum flooding surface. The SB and MFS are potentially correlative within the basin and support a global rapid sea-level fall previously proposed for this interval. The interpretation of the Prygorodok Fm. as coastal lake deposits may explain the unusual δ¹³C_carb values and constitute one of the few records of this type of environment identified in the early Paleozoic.     

ATP and its N<Superscript>6</Superscript>-substituted analogues: parameterization,molecular dynamics simulation and conformational analysis

In this work we used a combination of classical molecular dynamics and simulated annealing techniques to shed more light on the conformational flexibility of 12 adenosine triphosphate (ATP) analogues in a water environment. We present simulations in AMBER force field for ATP and 12 published analogues [Shah et al. (1997) Proc Natl Acad Sci USA 94: 3565–3570]. The calculations were carried out using the generalized Born (GB) solvation model in the presence of the cation Mg²⁺. The ion was placed at a close distance (2 Å) from the charged oxygen atoms of the beta and gamma phosphate groups of the ?3 negatively charged ATP analogue molecules. Analysis of the results revealed the distribution of inter-proton distances H8–H1′ and H8–H2′ versus the torsion angle ψ (C4–N9-C1′–O4′) for all conformations of ATP analogues. There are two gaps in the distribution of torsion angle ψ values: the first is between ?30 and 30 degrees and is described by cis-conformation; and the second is between 90 and 175 degrees, which mostly covers a region of anti conformation. Our results compare favorably with results obtained in experimental assays [Jiang and Mao (2002) Polyhedron 21:435–438].

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Figure Dihedral O4′–C1′–N9–C4 angle dependence on inter-proton distances H8–H1′ (crosses) and H8–H2′ (dots) measured for ATP

     

Summer zooplankton in small rivers in relation to selected conditions

The abundance and the biodiversity of summer zooplankton in the waters of the Drawa drainage (NW Poland) were studied, as was their relation to selected environmental conditions. The conditions upstream, especially in the outlets of lakes, did not affect the zooplankton communities downstream. This was also true of tributaries which had no influence on the shape of the zooplankton communities in the main river. The number of zooplankton in the outlets of eutrophic lakes was greater than in those of mesotrophic lakes. Increased vegetation cover significantly affected mainly the crustacean communities of zooplankton. Larger amounts of zooplankton were observed in rivers where the riparian zone was not covered with vegetation, but this difference was not significant. The hydrological conditions of the rivers and the Secchi depth visibility strongly impacted the composition of the zooplankton. The influence of abiotic factors was most pronounced on the abundance of cladocerans, and least pronounced on the abundance of rotifers.     

Applications of the ETS-NOCV method in descriptions of chemical reactions

The present study characterizes changes in the electronic structure of reactants during chemical reactions based on the combined charge and energy decomposition scheme, ETS-NOCV (extended transition state–natural orbitals for chemical valence). Decomposition of the activation barrier, ΔE ^#, into stabilizing (orbital interaction, ΔE _orb, and electrostatic, ΔE _elstat) and destabilizing (Pauli repulsion, ΔE _Pauli, and geometry distortion energy, ΔE _dist) factors is discussed in detail for the following reactions: (I) hydrogen cyanide to hydrogen isocyanide, HCN → CNH isomerization; (II) Diels-Alder cycloaddition of ethene to 1,3-butadiene; and two catalytic processes, i.e., (III) insertion of ethylene into the metal-alkyl bond using half-titanocene with phenyl-phenoxy ligand catalyst; and (IV) B–H bond activation catalyzed by an Ir-containing catalyst. Various reference states for fragments were applied in ETS-NOCV analysis. We found that NOCV-based deformation densities (Δρ _i) and the corresponding energies ΔE _orb(i) obtained from the ETS-NOCV scheme provide a very useful picture, both qualitatively and quantitatively, of electronic density reorganization along the considered reaction pathways. Decomposition of the barrier ΔE^# into stabilizing and destabilizing contributions allowed us to conclude that the main factor responsible for the existence of positive values of ΔE ^# for all processes (I, II, III and IV) is Pauli interaction, which is the origin of steric repulsion. In addition, in the case of reactions II, III and IV, a significant degree of structural deformation of the reactants, as measured by the geometry distortion energy, plays an important role. Depending on the reaction type, stabilization of the transition state (relatively to the reactants) originating either from the orbital interaction term or from electrostatic attraction can be of vital importance. Finally, use of the ETS-NOCV method to describe catalytic reactions allows extraction of information on the role of catalysts in determination of ΔE ^#.     

At the north-eastern extremity: variation in <Emphasis Type="Italic">Cepaea nemoralis</Emphasis> around Gdańsk,northern Poland

Variation in the shell colour and banding polymorphism in the land snail Cepaea nemoralis was studied in 260 populations in the region of Gdańsk, northern Poland. Unlike in other regions of Poland, many populations contain brown shells. Populations from shaded habitats have higher frequencies of brown than those from open and intermediate habitats, largely at the expense of yellow shells. Nearly all brown shells are also unbanded. Apart from this disequilibrium, banding morphs among yellow and pink shells show no relationship to habitat. There are no broad geographical trends in morph-frequencies, but there are very strong correlations among populations very close together, revealed both by pairwise analysis and Moran’s I. Principal Component Analyses show that these correlations relate to overall genetic similarity at the loci involved. The populations are at the north-eastern limits of the species’ range; habitats are mostly anthropogenic, and comparisons with studies in two urban areas (Wrocław, SW Poland, and Sheffield, central England) suggest that the patterns of variation seen are a product of human transport of propagules followed by local dispersal. The effect of habitat here is much less marked than in regions much further west, but it indicates that natural selection has occurred.     

Erratum to: Development of SCAR markers for rapid and specific detection of Pseudomonas syringae pv. morsprunorum races 1 and 2, using conventional and real-time PCR

Applied Microbiology and Biotechnology -