1,25-dihydroxyvitamin D3 Protects against Macrophage-Induced Activation of NFκB and MAPK Signalling and Chemokine Release in Human Adipocytes

Increased accumulation of macrophages in adipose tissue in obesity is linked to low-grade chronic inflammation, and associated with features of metabolic syndrome. Vitamin D₃ may have immunoregulatory effects and reduce adipose tissue inflammation, although the molecular mechanisms remain to be established. This study investigated the effects of vitamin D₃ on macrophage-elicited inflammatory responses in cultured human adipocytes, particularly the signalling pathways involved. Macrophage-conditioned (MC) medium (25% with adipocyte maintenance media) markedly inhibited protein expression of the nuclear factor-κB (NFκB) subunit inhibitor κBα (IκBα) (71%, P<0.001) and increased NFκB p65 (1.5-fold, P = 0.026) compared with controls. Treatment with 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) abolished macrophage-induced activation of NFκB signalling by increasing IκBα expression (2.7-fold, P = 0.005) and reducing NFκB p65 phosphorylation (68%; P<0.001). The mitogen-activated protein kinase (MAPK) signalling was activated by MC medium, which was also blunted by 1,25(OH)₂D₃ with a downregulation of phosphorylated p38 MAPK (32%, P = 0.005) and phosphorylated Erk1/2 (49%, P = 0.001). Furthermore, MC medium (12.5% or 25%) dose-dependently upregulated secretion of key proinflammatory chemokines/cytokines (22-368-fold; all P<0.001) and this was significantly decreased by 1,25(OH)₂D₃: IL-8 (61% and 31%, P<0.001), MCP-1 (37%, P<0.001 and 36%, P = 0.002), RANTES (78% and 62%, P<0.001) and IL-6 (29%, P<0.001 and 34%, P = 0.019). Monocyte migration-elicited by adipocytes treated with 1,25(OH)₂D₃ was also reduced (up to 25%, P<0.001). In conclusion, vitamin D₃ could be anti-inflammatory in adipose tissue, decreasing macrophage-induced release of chemokines and cytokines by adipocytes and the chemotaxis of monocytes. Our data suggests these effects are mediated by inhibition of the NFκB and MAPK signalling pathways.     

Mathematical analysis of the dependence of cell potential on external potassium in corn roots

The K⁺ dependence of normal (ψ) and diffusion (ψ_D) potentials in corn roots [Zea mays L., hybrid (A619 × Oh43) × A632] was determined experimentally and analyzed with respect to the parameter ξ [defined as exp (F ψ/RT)]. In the presence of 10 micromolar carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), ψ behaved as expected of a diffusion potential. Based upon the assumptions (a) that FCCP did not change any term of the Goldman-Hodgkin-Katz equation, and (b) that total potential was functionally the algebraic sum of ψ_D and ψ_P (the deviation from ψ_D due to an electrogenic system), ψ_P was found to be a complex function of external potassium and to have a minimum value of 0.69 millimolar K ion activity outside the cell. Analysis of ψ allowed us to develop an equation which predicts a complicated K⁺ dependence of ψ such as that found by Mertz and Higinbotham (Membrane Transport in Plants and Plant Organelles. Springer-Verlag 1974).     

The unstructured C-terminus of the tau subunit of Escherichia coli DNA polymerase III holoenzyme is the site of interaction with the alpha subunit

The τ subunit of Escherichia coli DNA polymerase III holoenzyme interacts with the α subunit through its C-terminal Domain V, τ_C16. We show that the extreme C-terminal region of τ_C16 constitutes the site of interaction with α. The τ_C16 domain, but not a derivative of it with a C-terminal deletion of seven residues (τ_C16Δ7), forms an isolable complex with α. Surface plasmon resonance measurements were used to determine the dissociation constant (K_D) of the α−τ_C16 complex to be ~260pM. Competition with immobilized τ_C16 by τ_C16 derivatives for binding to α gave values of K_D of 7μM for the α−τ_C16Δ7 complex. Low-level expression of the genes encoding τ_C16 and τ_C167, but not τ_C16Δ11, is lethal to E. coli. Suppression of this lethal phenotype enabled selection of mutations in the 3′ end of the τ_C16 gene, that led to defects in α binding. The data suggest that the unstructured C-terminus of τ becomes folded into a helix–loop–helix in its complex with α. An N-terminally extended construct, τ_C24, was found to bind DNA in a salt-sensitive manner while no binding was observed for τ_C16, suggesting that the processivity switch of the replisome functionally involves Domain IV of τ.     

Streptococcus pyogenes pSM19035 requires dynamic assembly of ATP-bound ParA and ParB on parS DNA during plasmid segregation

The accurate partitioning of Firmicute plasmid pSM19035 at cell division depends on ATP binding and hydrolysis by homodimeric ATPase δ₂ (ParA) and binding of ω₂ (ParB) to its cognate parS DNA. The 1.83 Å resolution crystal structure of δ₂ in a complex with non-hydrolyzable ATPγS reveals a unique ParA dimer assembly that permits nucleotide exchange without requiring dissociation into monomers. In vitro, δ₂ had minimal ATPase activity in the absence of ω₂ and parS DNA. However, stoichiometric amounts of ω₂ and parS DNA stimulated the δ₂ ATPase activity and mediated plasmid pairing, whereas at high (4:1) ω₂ : δ₂ ratios, stimulation of the ATPase activity was reduced and δ₂ polymerized onto DNA. Stimulation of the δ₂ ATPase activity and its polymerization on DNA required ability of ω₂ to bind parS DNA and its N-terminus. In vivo experiments showed that δ₂ alone associated with the nucleoid, and in the presence of ω₂ and parS DNA, δ₂ oscillated between the nucleoid and the cell poles and formed spiral-like structures. Our studies indicate that the molar ω₂ : δ₂ ratio regulates the polymerization properties of (δ•ATP•Mg²⁺)₂ on and depolymerization from parS DNA, thereby controlling the temporal and spatial segregation of pSM19035 before cell division.     

Salinity Effects on Water Potential Components and Bulk Elastic Modulus of Alternanthera philoxeroides (Mart.) Griseb

Pressure volume curves for Alternanthera philoxeroides (Mart.) Griseb. (alligator weed) grown in 0 to 400 millimolar NaCl were used to determine water potential (Ψ), osmotic potential (ψ_s), turgor potential (ψ_p) and the bulk elastic modulus (ε) of shoots at different tissue water contents. Values of ψ_s decreased with increasing salinity and tissue Ψ was always lower than rhizosphere Ψ. The relationship between ψ_p and tissue water content changed because ε increased with salinity. As a result, salt-stressed plants had larger ranges of positive turgor but smaller ranges of tissue water content over which ψ_p was positive. To our knowledge, this is the first report of such a salinity effect on ε in higher plants. These increases in ε with salinity provided a mechanism by which a large difference between plant Ψ and rhizosphere Ψ, the driving force for water uptake, could be produced with relatively little water loss by the plant. A time-course study of response after salinization to 400 millimolar NaCl showed Ψ was constant within 1 day, ψ_s and ψ_p continued to change for 2 to 4 days, and ε continued to change for 4 to 12 days. Changes in ε modified the capacity of alligator weed to maintain a positive water balance and consideration of such changes in other species of higher plants should improve our understanding of salt stress.     

Water transport in the midrib tissue of maize leaves : direct measurement of the propagation of changes in cell turgor across a plant tissue

Water movement across plant tissues occurs along two paths: from cell-to-cell and in the apoplasm. We examined the contribution of these two paths to the kinetics of water transport across the parenchymatous midrib tissue of the maize (Zea mays L.) leaf. Water relations parameters (hydraulic conductivity, Lp; cell elastic coefficient, ε; half-time of water exchange for individual cells, T_½) of individual parenchyma cells determined with the pressure probe varied in different regions of the midrib. In the adaxial region, Lp = (0.3 ± 0.3)·10⁻⁵ centimeters per second per bar, ε = 103 ± 72 bar, and T_½ = 7.9 ± 4.8 seconds (n = seven cells); whereas, in the abaxial region, Lp = (2.5 ± 0.9)·10⁻⁵ centimeters per second per bar, ε = 41 ± 9 bar, and T_½ = 1.3 ± 0.5 seconds (n = 7). This zonal variation in Lp, ε, and T_½ indicates that tissue inhomogeneities exist for these parameters and could have an effect on the kinetics of water transport across the tissue.

The diffusivity of the tissue to water (D_t) obtained from the sorption kinetics of rehydrating tissue was D_t = (1.1 ± 0.4)·10⁻⁶ square centimeters per second (n = 6). The diffusivity of the cell-to-cell path (D_c) calculated from pressure probe data ranged from D_c = 0.4·10⁻⁶ square centimeters per second in the adaxial region to D_c = 6.1·10⁻⁶ square centimeters per second in the abaxial region of the tissue. D_t D_c suggests substantial cell-to-cell transport of water occurred during rehydration. However, the tissue diffusivity calculated from the kinetics of pressure-propagation across the tissue (D_t′) was D_t′ = (33.1 ± 8.0)·10⁻⁶ square centimeters per second (n = 8) and more than 1 order of magnitude larger than D_t. Also, the hydraulic conductance of the midrib tissue (Lp_m per square centimeter of surface) estimated from pressure-induced flows across several parenchyma cell layers was Lp_m = (8.9 ± 5.6)·10⁻⁵ centimeters per second per bar (n = 5) and much larger than Lp.

These results indicate that the preferential path for water transport across the midrib tissue depends on the nature of the driving forces present within the tissue. Under osmotic conditions, the cell-to-cell path dominates, whereas under hydrostatic conditions water moves primarily in the apoplasm.

     

Random Coil to Globular Thermal Response of a Protein (H3.1) with Three Knowledge-Based Coarse-Grained Potentials

The effect of temperature on the conformation of a histone (H3.1) is studied by a coarse-grained Monte Carlo simulation based on three knowledge-based contact potentials (MJ, BT, BFKV). Despite unique energy and mobility profiles of its residues, the histone H3.1 undergoes a systematic (possibly continuous) structural transition from a random coil to a globular conformation on reducing the temperature. The range over which such a systematic response in variation of the radius of gyration (R_g) with the temperature (T) occurs, however, depends on the potential, i.e. ΔT_MJ ≈ 0.013–0.020, ΔT_BT ≈ 0.018–0.026, and ΔT_BFKV ≈ 0.006–0.013 (in reduced unit). Unlike MJ and BT potentials, results from the BFKV potential show an anomaly where the magnitude of R_g decreases on raising the temperature in a range ΔT_A ≈ 0.015–0.018 before reaching its steady-state random coil configuration. Scaling of the structure factor, S(q) ∝ q^−1/ν, with the wave vector, q = 2π/λ, and the wavelength, λ, reveals a systematic change in the effective dimension (D_e∼1/ν) of the histone with all potentials (MJ, BT, BFKV): D_e∼3 in the globular structure with D_e∼2 for the random coil. Reproducibility of the general yet unique (monotonic) structural transition of the protein H3.1 with the temperature (in contrast to non-monotonic structural response of a similar but different protein H2AX) with three interaction sets shows that the knowledge-based contact potential is viable tool to investigate structural response of proteins. Caution should be exercise with the quantitative comparisons due to differences in transition regimes with these interactions.     

Transpiration- and growth-induced water potentials in maize

Recent evidence from leaves and stems indicates that gradients in water potential (ψ_w) necessary for water movement through growing tissues are larger than previously assumed. Because growth is sensitive to tissue ψ_w and the behavior of these gradients has not been investigated in transpiring plants, we examined the water status of all the growing and mature vegetative tissues of maize (Zea mays L.) during high and low rates of transpiration. The ψ_w measured in the mature regions of the plant responded primarily to transpiration, while the ψ_w in the growing regions was affected both by transpiration and growth. The transpiration-induced potentials of the mature tissue formed a gradient of decreasing ψ_w along the transpiration stream while the growth-induced potentials formed a gradient of decreasing ψ_w from the transpiration stream to the expanding cells in the growing tissue. The growth-induced gradient in ψ_w within the leaf remained fairly constant as the xylem ψ_w decreased during the day and was associated with a decreased osmotic potential (ψ_s) of the growing region (osmotic adjustment). The growth-induced gradient in ψ_w was not caused by excision of the tissue because intact maize stems exhibited a similar ψ_w. These observations support the concept that large gradients in ψ_w are required to maintain water flow to expanding cells within all the vegetative tissues and suggest that the maintenance of a favorable gradient in ψ_w for cell enlargement may be an important role for osmotic adjustment.     

Cross-Correlation Functions for a Neuronal Model

Cross-correlation functions, R_XY(t,τ), are obtained for a neuron model which is characterized by constant threshold θ, by resetting to resting level after an output, and by membrane potential U(t) which results from linear summation of excitatory postsynaptic potentials h(t). The results show that: (1) Near time lag τ = 0, R_XY(t,τ) = f_U [θ-h(τ), t + τ] {h′(τ) + E_U [u′(t + τ)]} for positive values of this quantity, where f_U(u,t) is the probability density function of U(t) and E_U [u′(t + τ)] is the mean value function of U′(t + τ). (2) Minima may appear in R_XY(t,τ) for a neuron subjected only to excitation. (3) For large τ, R_XY(t,τ) is given approximately by the convolution of the input autocorrelation function with the functional of point (1). (4) R_XY(t,τ) is a biased estimator of the shape of h(t), generally over-estimating both its time to peak and its rise time.     

Early Picosecond Events in the Photocycle of Bacteriorhodopsin

The primary processes of the photochemical cycle of light-adapted bacteriorhodopsin (BR) were studied by various experimental techniques with a time resolution of 5 × 10^-13 s. The following results were obtained. (a) After optical excitation the first excited singlet state S₁ of bacteriorhodopsin is observed via its fluorescence and absorption properties. The population of the excited singlet state decays with a lifetime τ₁ of ~0.7 ps (430 ± 50 fs) (52). (b) With the same time constant the first ground-state intermediate J builds up. Its absorption spectrum is red-shifted relative to the spectrum of BR by ~30 nm. (c) The second photoproduct K, which appears with a time constant of τ₂ = 5 ps shows a red-shift of 20 nm, relative to the peak of BR. Its absorption remains constant for the observation time of 300 ps. (d) Upon suspending bacteriorhodopsin in D₂O and deuterating the retinal Schiff base at its nitrogen (lysine 216), the same photoproducts J and K are observed. The relaxation time constants τ₁ and τ₂ remain unchanged upon deuteration within the experimental accuracy of 20%.     

Simulation of Interstitial Fluid Flow in Ligaments: Comparison among Stokes,Brinkman and Darcy Models

In this paper, we use Stokes, Brinkman and Darcy equations to approximate the porous continuum media of ligament tissues respectively, simulate the flow field with FLUENT software, and study the shear stress on the cell surface due to the interstitial fluid flow. Since the Brinkman equation approaches Stokes equation well in high hydraulic permeability (k_p) condition (k_p ≥1.0×10^-8 m² in our numerical simulation), and it is an approximation to Darcy model in low k_p condition (k_p ≤5.0×10^-12 m² in our numerical simulation), we used the Brinkman model to simulate the interstitial fluid flow in the ligament where k_p is approximately 1.0×10^-16 m². It shows k_p and anisotropic property have a little effect on the flow field, but have a great effect on the shear stress on the membrane of interstitial cells (τ_cell). There is a linear relationship between τ_cell and , when k_p =1.0×10^-16 m² and the maximum τ_cell (τ_cell,max) is approximately 10 Pa. The anisotropic property will affect τ_cell''s distribution on the cell surface. When k_x/k_y>1, low τ_cell dominates the cell, while when k_x/k_y<1, high τ_cell dominants the cell.     

Ribosylation Rapidly Induces α-Synuclein to Form Highly Cytotoxic Molten Globules of Advanced Glycation End Products

Background

Alpha synuclein (α-Syn) is the main component of Lewy bodies which are associated with several neurodegenerative diseases such as Parkinson''s disease. While the glycation with D-glucose that results in α-Syn misfold and aggregation has been studied, the effects of glycation with D-ribose on α-Syn have not been investigated.

Methodology/Principal Findings

Here, we show that ribosylation induces α-Syn misfolding and generates advanced glycation end products (AGEs) which form protein molten globules with high cytotoxcity. Results from native- and SDS-PAGE showed that D-ribose reacted rapidly with α-Syn, leading to dimerization and polymerization. Trypsin digestion and sequencing analysis revealed that during ribosylation the lysinyl residues (K₅₈, K₆₀, K₈₀, K₉₆, K₉₇ and K₁₀₂) in the C-terminal region reacted more quickly with D-ribose than those of the N-terminal region. Using Western blotting, AGEs resulting from the glycation of α-Syn were observed within 24 h in the presence of D-ribose, but were not observed in the presence of D-glucose. Changes in fluorescence at 410 nm demonstrated again that AGEs were formed during early ribosylation. Changes in the secondary structure of ribosylated α-Syn were not clearly detected by CD spectrometry in studies on protein conformation. However, intrinsic fluorescence at 310 nm decreased markedly in the presence of D-ribose. Observations with atomic force microscopy showed that the surface morphology of glycated α-Syn looked like globular aggregates. thioflavin T (ThT) fluorescence increased during α-Syn incubation regardless of ribosylation. As incubation time increased, ribosylation of α-Syn resulted in a blue-shift (∼100 nm) in the fluorescence of ANS. The light scattering intensity of ribosylated α-Syn was not markedly different from native α-Syn, suggesting that ribosylated α-Syn is present as molten protein globules. Ribosylated products had a high cytotoxicity to SH-SY5Y cells, leading to LDH release and increase in the levels of reactive oxygen species (ROS).

Conclusions/Significance

α-Syn is rapidly glycated in the presence of D-ribose generating molten globule-like aggregations which cause cell oxidative stress and result in high cytotoxicity.     

Molecular Anatomy of ParA-ParA and ParA-ParB Interactions during Plasmid Partitioning

Firmicutes multidrug resistance inc18 plasmids encode parS sites and two small homodimeric ParA-like (δ₂) and ParB-like (ω₂) proteins to ensure faithful segregation. Protein ω₂ binds to parS DNA, forming a short left-handed helix wrapped around the full parS, and interacts with δ₂. Protein δ₂ interacts with ω₂ and, in the ATP-bound form, binds to nonspecific DNA (nsDNA), forming small clusters. Here, we have mapped the ω₂·δ₂ and δ₂·δ₂ interacting domains in the δ₂ that are adjacent to but distinct from each other. The δ₂ nsDNA binding domain is essential for stimulation of ω₂·parS-mediated ATP hydrolysis. From the data presented here, we propose that δ₂ interacts with ATP, nsDNA, and with ω₂ bound to parS at near equimolar concentrations, facilitating a δ₂ structural transition. This δ₂ “activated” state overcomes its impediment in ATP hydrolysis, with the subsequent release of both of the proteins from nsDNA (plasmid unpairing).     

Spatial Distribution of Potential in a Flat Cell: Application to the Catfish Horizontal Cell Layers

An analytical solution is obtained for the three-dimensional spatial distribution of potential inside a flat cell, such as the layer of horizontal cells, as a function of its geometry and resistivity characteristics. It was found that, within a very large range of parameter values, the potential is given by [Formula: see text] where r = ρ/ρ₀, = z/ρ₀, ρ = (R_i/R_m)·ρ₀, δ = h/ρ₀; K is a constant; J is the assumed synaptic current; ρ, z are cylindrical coordinates; ρ₀ is the radius of the synaptic area of excitation; h is the cell thickness; and R_i, R_m are the intracellular and membrane resistivities, respectively. Formula A closely fits data for the spatial decay of potential which were obtained from the catfish internal and external horizontal cells. It predicts a decay which is exponential down to about 40% of the maximum potential but is much slower than exponential below that level, a characteristic also exhibited by the data. Such a feature in the decay mode allows signal integration over the large retinal areas which have been observed experimentally both at the horizontal and ganglion cell stages. The behavior of the potential distribution as a function of the flat cell parameters is investigated, and it is found that for the range of the horizontal cell thicknesses (10-50 μ) the decay rate depends solely on the ratio R_m/R_i. Data obtained from both types of horizontal cells by varying the diameter of the stimulating spot and for three widely different intensity levels were closely fitted by equation A. In the case of the external horizontal cell, the fit for different intensities was obtained by varying the ratio R_m/R_i; in the case of the internal horizontal cell it was found necessary, in order to fit the data for different intensities, to vary the assumed synaptic current J.     

Simple Uniaxial and Uniform Biaxial Deformation of Nearly Isotropic Incompressible Tissues

A method is developed for analyzing in a unified manner both uniaxial and uniform biaxial strain data obtained from nearly isotropic tissues. The formulation is a direct application of nonlinear elasticity theory pertaining to large deformations. The general relation between Eulerian stress (σ) and extension ratio (λ) in soft isotropic elastic bodies undergoing uniform deformation takes the simple form: σ = ((λ³ - 1)/λ) f(λ), where f(λ) must be determined for each material. The extension ratio may be either greater than 1.0 (uniaxial elongation), or lie between zero and 1.0 (uniform biaxial extension). Simple analytical functions for f(λ) are most readily found for each tissue by plotting all data as (λ³ - 1)/λσ vs. λ. Of those tissues investigated in this way (dog pericardium and pleura, and cat mesentery and dura), all but pleura could be adequately described by a parabola: 1/f(λ) = 1/k{[(λ_M - λ)(λ - λ_m)]/[λ_M - λ_m}. In these instances, three material constants per tissue (K, λ_M, λ_m) served to predict approximately the stresses attained during both small and large deformations, in strips and sheets alike. It was further found that the uniaxial strain asymptote (λ_M) was linearly related to the biaxial strain asymptote (Λ_M), thus effectively reducing the number of constants by one.     

NMR solution structures of Runella slithyformis RNA 2′-phosphotransferase Tpt1 provide insights into NAD+ binding and specificity

Tpt1, an essential component of the fungal and plant tRNA splicing machinery, catalyzes transfer of an internal RNA 2′-PO₄ to NAD⁺ yielding RNA 2′-OH and ADP-ribose-1′,2′-cyclic phosphate products. Here, we report NMR structures of the Tpt1 ortholog from the bacterium Runella slithyformis (RslTpt1), as apoenzyme and bound to NAD⁺. RslTpt1 consists of N- and C-terminal lobes with substantial inter-lobe dynamics in the free and NAD⁺-bound states. ITC measurements of RslTpt1 binding to NAD⁺ (K_D ∼31 μM), ADP-ribose (∼96 μM) and ADP (∼123 μM) indicate that substrate affinity is determined primarily by the ADP moiety; no binding of NMN or nicotinamide is observed by ITC. NAD⁺-induced chemical shift perturbations (CSPs) localize exclusively to the RslTpt1 C-lobe. NADP⁺, which contains an adenylate 2′-PO₄ (mimicking the substrate RNA 2′-PO₄), binds with lower affinity (K_D ∼1 mM) and elicits only N-lobe CSPs. The RslTpt1·NAD⁺ binary complex reveals C-lobe contacts to adenosine ribose hydroxyls (His99, Thr101), the adenine nucleobase (Asn105, Asp112, Gly113, Met117) and the nicotinamide riboside (Ser125, Gln126, Asn163, Val165), several of which are essential for RslTpt1 activity in vivo. Proximity of the NAD⁺ β-phosphate to ribose-C1″ suggests that it may stabilize an oxocarbenium transition-state during the first step of the Tpt1-catalyzed reaction.     

Elastic-Mathematical Theory of Cells and Mitochondria in Swelling Process: II. Effect of Temperature upon Modulus of Elasticity of Membranous Material of Egg Cells of Sea Urchin, Strongylocentrotus purpuratus, and of Oyster, Crassostrea virginica

The elastic behavior of the cell wall as a function of the temperature has been studied with particular attention being given to the swelling of egg cells of Strongylocentrotus purpuratus and Crassostrea virginica in different sea water concentrations at different temperatures. It was found that the modulus of elasticity is a nonlinear function of temperature. At about 12-13°C the modulus of elasticity (E) is constant, independent of the stress (σ) and strain (ε_ν) which exist at the cell wall; the membranous material follows Hooke's law, and E ≈ 3 × 10⁷ dyn/cm² for S. purpuratus and C. virginica. When the temperature is higher or lower than 12-13°C, the modulus of elasticity increases, and the membranous material does not follow Hooke's law, but is almost directly proportional to the stresses existing at the cell wall. On increasing the stress, the function E_σ = E(σ) approaches saturation. The corresponding stress-strain diagrams, σ = σ(ε_ν), and the graphs, E_σ = E(σ) and E_σ = E(t) are given. The cyto-elastic phenomena at the membrane are discussed.     

High genetic diversity at the extreme range edge: nucleotide variation at nuclear loci in Scots pine (Pinus sylvestris L.) in Scotland

Nucleotide polymorphism at 12 nuclear loci was studied in Scots pine populations across an environmental gradient in Scotland, to evaluate the impacts of demographic history and selection on genetic diversity. At eight loci, diversity patterns were compared between Scottish and continental European populations. At these loci, a similar level of diversity (θ_sil=∼0.01) was found in Scottish vs mainland European populations, contrary to expectations for recent colonization, however, less rapid decay of linkage disequilibrium was observed in the former (ρ=0.0086±0.0009, ρ=0.0245±0.0022, respectively). Scottish populations also showed a deficit of rare nucleotide variants (multi-locus Tajima''s D=0.316 vs D=−0.379) and differed significantly from mainland populations in allelic frequency and/or haplotype structure at several loci. Within Scotland, western populations showed slightly reduced nucleotide diversity (π_tot=0.0068) compared with those from the south and east (0.0079 and 0.0083, respectively) and about three times higher recombination to diversity ratio (ρ/θ=0.71 vs 0.15 and 0.18, respectively). By comparison with results from coalescent simulations, the observed allelic frequency spectrum in the western populations was compatible with a relatively recent bottleneck (0.00175 × 4N_e generations) that reduced the population to about 2% of the present size. However, heterogeneity in the allelic frequency distribution among geographical regions in Scotland suggests that subsequent admixture of populations with different demographic histories may also have played a role.     

Primary Events, Energy Transfer, and Reactions in Photosynthetic Events: Lifetime of the Excited State In Vivo: II. Bacteriochlorophyll in Photosynthetic Bacteria at Room Temperature

Lifetime of the excited state (τ) of bacteriochlorophyll (BChl) in photosynthetic bacteria, measured with a mode-locked argon laser (oscillating at 488 nm; mode locked at 56 MHz) as light source, ranged from 0.3 to 2.5 nsec. These τ values are reported with a precision of ±0.1 nsec. The value of τ at high exciting light intensity (I) was two to three times that at low intensity. For young cultures of green bacterium Chloropseudomonas ethylicum, τ ranged from 0.5 (low I) to 1.0 nsec (high I); for those of the purple bacterium Rhodospirillum rubrum, from 0.4 (low I) to 1.0 nsec (high I); and for those of the BChl b-containing Rhodopseudomonas viridis, from 1.0 (low I) to 2.5 nsec (high I). These data provide information regarding the efficiencies of the photochemical process in these bacteria. Quantum yield (ø) of BChl fluorescence, calculated from ø = τ/τ₀ (where τ₀ is the intrinsic lifetime of fluorescence), ranges from 2-6% at low intensities to 6-14% at high intensities.