Identification of a new <Emphasis Type="Italic">Vrn</Emphasis>-<Emphasis Type="Italic">B1</Emphasis> allele using two near-isogenic wheat lines with difference in heading time

We conducted a molecular analysis of the Vrn-B1 gene in two near-isogenic lines (NILs) carrying the dominant Vrn-B1 ^S and Vrn-B1 ^Dm alleles from the Saratovskaya 29 and Diamant 2 cultivars, respectively. These lines are characterized by different times of ear emergence. PCR analysis and subsequent sequencing of the regulatory regions of Vrn-B1 revealed the full identity of the promoter region in both alleles. Simultaneously, we found significant differences in the structure of the first intron of the Vrn-B1 ^S allele when compared to Vrn-B1 ^Dm ; specifically, the deletion of 0.8 kb coupled with the duplication of 0.4 kb. We suggest that these changes in intron 1 of Vrn-B1 ^S caused earlier ear emergence in the corresponding NIL. The unusual structure of intron 1 within the Vrn-B1 ^S allele was described for the first time in this study. The allele Vrn-B1 ^Dm was almost identical with the previously studied sequence of the Vrn-B1a allele of T. aestivum, Triple Dirk B. We designated the new Vrn-B1 ^S allele as Vrn-B1c. PCR analysis of the Vrn-B1 gene in 26 spring wheat cultivars of both Russian and foreign breeding revealed that 16 of them contain the Vrn-B1a allele and 6 contain the Vrn-B1c allele. Other cultivars studied contained the recessive vrn-B1 gene, except for Novosibirskaya 67. This study demonstrates that the traditional system of Vrn-1 markers does not fully encompass the allelic diversity of these genes because none of the cultivars containing the Vrn-B1c allele gave a PCR product using the previously developed set of primers for identification of the Vrn-B1 locus. We showed that the newly characterized Vrn-B1c allele is widely distributed among different genotypes of spring wheat. The findings indicate the impact of structural changes in the first intron of Vrn-1 on the vernalization response and heading time.     

Peculiarities of cyanide binding to the <Emphasis Type="Italic">ba</Emphasis><Subscript>3</Subscript>-type cytochrome oxidase from the thermophilic bacterium <Emphasis Type="Italic">Thermus thermophilus</Emphasis>

Cytochrome c oxidase of the ba ₃-type from Thermus thermophilus does not interact with cyanide in the oxidized state and acquires the ability to bind heme iron ligands only upon reduction. Cyanide complexes of the reduced heme a ₃ in cytochrome ba ₃ and in mitochondrial aa ₃-type cytochrome oxidase are similar spectroscopically, but the a ₃²⁺-CN complex of cytochrome ba ₃ is strikingly tight. Experiments have shown that the K _d value of the cytochrome ba ₃ complex with cyanide in the presence of reductants of the enzyme binuclear center does not exceed 10⁻⁸ M, which is four to five orders of magnitude less than the K _d of the cyanide complex of the reduced heme a ₃ of mitochondrial cytochrome oxidase. The tightness of the cytochrome ba ₃ complex with cyanide is mainly associated with an extremely slow rate of the ligand dissociation (k _off ≤ 10⁻⁷ sec⁻¹), while the rate of binding (k _on ∼ 10² M⁻¹·sec⁻¹) is similar to the rate observed for the mitochondrial cytochrome oxidase. It is proposed that cyanide dissociation from the cytochrome ba ₃ binuclear center might be hindered sterically by the presence of the second ligand molecule in the coordination sphere of Cu_B²⁺. The rate of cyanide binding with the reduced heme a ₃ does not depend on pH in the neutral area, but it approaches linear dependence on H⁺ activity in the alkaline region. Cyanide binding appears to be controlled by protonation of an enzyme group with pK _a = 8.75.     

Membrane lipid dynamics and enzymic activity in bovine adrenal cortex microsomes

The lipid dynamics of the adrenocortical microsomal membranes was studied by monitoring the fluorescence anisotropy and excited state lifetime of a set of anthroyloxy fatty acid probes (2-, 7-, 9- and 12-(9-anthroyloxy)-stearic acid (AP) and 16-(9-anthroyloxy)palmitic acid (AS). It was found that a decreasing polarity gradient from the aqueous membrane interface to the membrane interior, was present. This gradient was not modified by the proteins, as evidenced by comparison of complete membranes and derived liposomes, suggesting that the anthroyloxy probes were not in close contact with the proteins. An important change of the value of the mean rotational relaxation time as a function of the position of the anthroyl ring along the acyl chain was evidenced. In the complete membranes, a relatively more fluid medium was evidenced in the C₁₆ as compared to the C₂ region, while the rotational motion appeared to be the most hindered at the C₇–C₉ level. In the derived liposomes, a similar trend was observed but the mobility was higher at all levels. The decrease of the mean rotational relaxation time was more important for 12-AS and 16-AP. Temperature dependence of the mean rotational relaxation time of 2-AS, 12-AS and 16-AP in the complete membranes revealed the existence of a lipid reorganization occurring around 27°C and concerning mainly the C₁₆ region. The extent to which the acyl chain reacted to this perturbation at the C₁₂ level depended on pH. The presence of proteins increased the apparent magnitude of this reorganization and also modified the critical temperature from approx. 23°C in the derived liposomes to approx. 27°C in the complete membranes. Thermal dependence of the maximum velocity of the $\text{3-}\text{oxosteroid}\text{Δ}{}^5\text{?Δ}{}^4\text{-}\text{isomerase}$, the second enzyme in the enzymatic sequence, responsible for the biosynthesis of the $\text{3-}\text{oxo}\text{-Δ}{}^4\text{-}\text{steroids}$ in the adrenal cortex microsomes, was studied. The activation energy of the catalyzed reaction was found to be low and constant ($\text{2–5}\text{kcal}\text{·}\text{mol}{}^{\mathrm{?1}}$) in the temperature range 16–40°C at pH 7.5, 8.5 and 9, corresponding to the minimum, intermediate and maximum rate, respectively. A drastic increase of the activation energy ($\text{20}\text{kcal}\text{·}\text{mol}{}^{\mathrm{?1}}$) was observed at temperature below 16°C at pH 7.5. A correlated change of the $\text{p}\text{K}{}_{\mathrm{<mtext>ES</mtext>}}{}^{\mathrm{<mtext>app</mtext>}}$ as function of temperature was detected; at 36°C $\text{p}\text{K}{}_{\mathrm{<mtext>ES</mtext>}}{}^{\mathrm{<mtext>app</mtext>}}\text{= 8.3}$ while at 13°C the value shifted to 8.7. The pH range of the group ionization was narrower at 13°C. In contrast with the behaviour of the $\text{3β-}\text{hydroxy}\text{-Δ}{}^5\text{-}\text{steroid dehydrogenase}$, the $\text{3-}\text{oxosteroid}\text{Δ}{}^5\text{?Δ}{}^4\text{-}\text{isomerase}$ was apparently unaffected by the lipid reorganization at 27°C. It is suggested that this enzyme possesses a different and more fluid lipid environment than the bulk lipids.     

Mathematical models for mixing in deep-jet bioreactors: Calculation of parameters

The macroscopic mathematical model based on compartments with ideal mixing zones and tanks-in series was evaluated. Based on the experimental data obtained in a 300 dm³ pilot reactor and the dependence of mixing time on the volume of liquid phase, we have found mathematical relations between the ratio of vessel diameter to liquid level, adjustable parameters of model and the mixing time.List of Symbols V dm³ total volume of bioreactor - V _g dm³ total volume of liquid - V ₁ dm³ volume of ideally mixed zone in the vessel - V ₂ dm³ volume of macromixer in inner circulation flows - V ₃ dm³ volume of liquid phase in the pump - V ₄ dm³ volume of liquid phase in the pipe between the vessel and the pump - V ₅ dm³ volume of liquid phase in the pipe between the pump and air input system included falling jet - V _LT dm³ volume of liquid in the tank - V _LC dm³ volume of liquid in the circulation system - F _E dm³/s inner volumetric circulation flow rate across the macromixers - F _cir dm³/s external volumetric circulation flow rate, pumping capacity - t _A s time interval of the pulse application - t _AA s time point of the pulse application related to the free choosen starting point of the experiment - t _m s mixing time - t _c s circulation time - t _end s end time of simulation - C _*,* kg/m³ concentration of tracer in the indicated compartment - C ₀ kg/m³ concentration of the tracer before the injection - C _t kg/m³ concentration of the tracer at the indicated time - C kg/m³ theoretical concentration of the full mixed tracer - C _sim kg/m³ calculated concentration of tracer during numerical integration method - i index of an arbitrary tank - D _T m diameter of bioreactor - D 1/s dilution rate - H _L m level of liquid in the unaerated vessel - vector of inhomogenities     

Kinetic study of dissociation of Eu(III) complex with H8dotp (H8dotp = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid))

The dissociation kinetics of the europium(III) complex with H₈dotp ligand was studied by means of molecular absorption spectroscopy in UV region at ionic strength 3.0 mol dm⁻³ (Na,H)ClO₄ and in temperature region 25-60 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLIFS) was employed in order to determine the number of water molecules in the first coordination sphere of the europium(III) reaction intermediates and the final products. This technique was also utilized to deduce the composition of reaction intermediates in course of dissociation reaction simultaneously with calculation of rate constants and it demonstrates the elucidation of intimate reaction mechanism. The thermodynamic parameters for the formation of kinetic intermediate (ΔH⁰ = 11 ± 3 kJ mol⁻¹, ΔS⁰ = 41 ± 11 J K⁻¹ mol⁻¹) and the activation parameters (E_a = 69 ± 8 kJ mol⁻¹, ΔH^≠ = 67 ± 8 kJ mol⁻¹, ΔS^≠ = −83 ± 24 J K⁻¹ mol⁻¹) for the rate-determining step describing the complex dissociation were determined. The mechanism of proton-assisted reaction was proposed on the basis of the experimental data.     

What can we learn about the lipid vesicle structure from the small-angle neutron scattering experiment?

Small-angle neutron scattering (SANS) on the unilamellar vesicle (ULV) populations (diameter 500 and 1,000 Å) in D₂O was used to characterize lipid vesicles from dimyristoylphosphatidylcholine (DMPC) at three phases: gel L_β′, ripple P_β′ and liquid L_α. Parameters of vesicle populations and internal structure of the DMPC bilayer were characterized on the basis of the separated form factor (SFF) model. Vesicle shape changes from nearly spherical in the L_α phase to elliptical in the P_β′ and L_β′ phases. This is true for vesicles prepared via extrusion through pores with the diameter 500 Å. Parameters of the internal bilayer structure (thickness of the membrane and the hydrophobic core, hydration and the surface area of the lipid molecule) were determined on the basis of the hydrophobic–hydrophilic (HH) approximation of neutron scattering length density across the bilayer ρ(x) and of the step function (SF) approximation of ρ(x). DMPC membrane thickness in the L_α phase (T=30°C) demonstrates a dependence on the membrane curvature for extruded vesicles. Prepared via extrusion through 500 Å diameter pores, vesicle population in the L_α phase has the following characteristics: average value of minor semi-axis 266±2 Å, ellipse eccentricity 1.11±0.02, polydispersity 26%, thickness of the membrane 48.9±0.2 Å and of the hydrophobic core 19.9±0.4 Å, surface area 60.7±0.5 Ų and number of water molecules 12.8±0.3 per DMPC molecule. Vesicles prepared via extrusion through pores with the diameter 1,000 Å have polydispersity of 48% and membrane thickness of 45.5±0.6 Å in the L_α phase. SF approximation was used to describe the DMPC membrane structure in L_β′ (T=10°C) and P_β′ (T=20°C) phases. Extruded DMPC vesicles in D₂O have membrane thickness of 49.6±0.5 Å in the L_β′ phase and 48.3±0.6 Å in the P_β′ phase. The dependence of the DMPC membrane thickness on temperature was restored from the SANS experiment.     

Ethylenesulfide as a useful agent for incorporation into the biopolymer chitosan in a solvent-free reaction for use in cation removal

Chitosan (Ch) was chemically modified with ethylenesulfide (Es) under solvent-free conditions to give (ChEs), displaying a high content of thiol groups due to opening of the three member cyclic reagent. Elemental analysis showed a decrease in nitrogen content. This result indicated the incorporation of two ethylenesulfide molecules for each unit of the polymeric structure of the precursor biopolymer. Infrared spectroscopy, thermogravimetry, and ¹³C NMR in the solid state demonstrated the effectiveness of the reaction, with signals at 30 ppm for ChEs due to the change in the methylene group environment. Divalent metal uptake by chemically modified biopolymer gave the order Cu > Ni > Co > Zn, reflecting the corresponding acidity of these cations in bonding to the sulfur and the basic nitrogen atoms available on the pendant chains. The equilibrium data were fitted to Freundlich, Temkin, and Langmuir models. The maximum monolayer adsorption capacity for the cations was found to be 1.54 ± 0.02, 1.25 ± 0.03, 1.13 ± 0.01, and 0.83 ± 0.03 mmol g⁻¹, respectively. The Langmuir model best explained the cation–sulfur bond interactions at the solid–liquid interface. The thermodynamics for these interactions gave exothermic enthalpic values of −43.02 ± 0.03, −28.72 ± 0.02, −26.27 ± 0.04, and −17.32 ± 0.02 kJ mol⁻¹, respectively. The spontaneity of the systems is given by negative Gibbs free energies of −31.2 ± 0.1, −32.7 ± 0.1, −31.7 ± 0.1, and −32.2 ± 0.1 kJ mol⁻¹, respectively, in spite of the unfavorable negative entropic values of −39 ± 1, −13 ± 1, −18 ± 1, and −49 ± 1 J K⁻¹ mol⁻¹ due to solvent ordering in the course of complexation. This newly synthesized biopolymer is presented as a chemically useful material for cation removal from aqueous solution.     

Roles of external and cellular Cl− ions on the activation of an apical electrodiffusional Cl− pathway in toad skin

Summary This study is concerned with the short-circuit current,I _sc, responses of the Cl^–-transporting cells of toad skin submitted to sudden changes of the external Cl^– concentration. [Cl]₀. Sudden changes of [Cl]₀, carried out under apical membrane depolarization, allowed comparison of the roles of [Cl]₀ and [Cl]_cell on the activation of the apical Cl^– pathways. Equilibration of shortcircuited skins symmetrically in K-Ringer's solutions of different Cl^– concentrations permitted adjustment of [Cl]_cell to different levels. For a given Cl^– concentration (in the range of 11.7 to 117mm) on both sides of a depolarized apical membrane, this structure exhibits a high Cl^– permeability,P _(Cl)apical. On the other hand, for the same range of [Cl]_cell but with [Cl]₀=0,P _(Cl)apical is reduced to negligible values. These observations indicate that when the apical membrane is depolarizedP _(Cl)apical is modulated by [Cl]₀; in the absence of external Cl^– ions, intracellular Cl^– is not sufficient to activateP _(Cl)apical. Computer simulation shows that the fast Cl^– currents induced across the apical membrane by sudden shifts of [Cl]₀ from a control equilibrium value strictly follow the laws of electrodiffusion. For each experimental group, the computer-generatedI _sc versus ([Cl]_cell–[Cl]₀) curve which best fits the experimental data can only be obtained by a unique pair ofP _(Cl)apical andR _b (resistance of the basolateral membrane), thus allowing the calculation of these parameters. The electrodiffusional behavior of the net Cl^– flux across the apical membrane supports the channel nature of the apical Cl^– pathways in the Cl^–-transporting cell. Cl^– ions contribute significantly to the overall conductance of the basolateral membrane even in the presence of a high K concentration in the internal solution.     

Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae

The binding affinity of the two substrate–water molecules to the water-oxidizing Mn₄CaO₅ catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S₂ and S₃ states by the exchange of bound ¹⁶O-substrate against ¹⁸O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: k_f = 52 ± 8 s^− 1 and k_s = 1.9 ± 0.3 s^− 1 in the S₂ state, and k_f = 42 ± 2 s^− 1 and k_slow = 1.2 ± 0.3 s^− 1 in S₃, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S₂ state, which confirms beyond doubt that both substrate–water molecules are already bound in the S₂ state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S₂ → S₃ transition. Implications for recent models for water-oxidation are briefly discussed.     

沙质草地3种优势植物叶片光合生理对增温和降水减少的响应北大核心CSCD

以沙质草地优势物种猪毛蒿、胡枝子和糙隐子草为研究对象,利用开顶式生长室(OTC)模拟增温,研究降水减少20%、40%和60%与增温的交互作用对3种典型植物叶片光合气体交换特征及叶绿素荧光特征的影响,以揭示沙质草地3种优势植物对气候变化的响应规律。结果显示:(1)与自然温度相比,OTC模拟增温增加了猪毛蒿C_(i),显著降低了胡枝子G_(s)、P_(n)和T_(r)、糙隐子草G_(s)和P_(n)、猪毛蒿WUE和L_(s),也显著降低了猪毛蒿和胡枝子F_(v)/F_(m)和F_(v)/F_(o)。(2)无论增温与否,随着降水减少幅度的增加,猪毛蒿G_(s)和P_(n)呈下降趋势,且中度以上的干旱胁迫下(降水减少>40%)胡枝子和糙隐子草P_(n)显著低于对照。(3)在自然温度条件下,轻度干旱胁迫时(降水减少20%)猪毛蒿T_(r)显著低于对照,重度干旱胁迫时(降水减少60%)其WUE、F_(v)/F_(m)和F_(v)/F_(o)显著低于对照;重度干旱胁迫时,胡枝子C_(i)显著高于对照,差异幅度达10.7%,L_(s)显著低于对照,轻度干旱胁迫时(降水减少20%)其F_(v)/F_(m)和F_(v)/F_(o)显著高于中度以上的干旱胁迫;中度以上的干旱胁迫下糙隐子草T_(r)和G_(s)显著低于对照,重度干旱胁迫时,其C_(i)、F_(v)/F_(m)和F_(v)/F_(o)显著低于对照,WUE和L_(s)显著高于对照。(4)增温与降水减少交互作用下,所有处理猪毛蒿C_(i)均高于对照,差异幅度分别达4.5%,6.0%和8.4%;胡枝子T_(r)均显著低于对照,差异幅度达57.8%;重度干旱胁迫时猪毛蒿L_(s)和WUE显著低于对照,糙隐子草F_(v)/F_(m)和F_(v)/F_(o)随降水减少而降低,中度以上的干旱胁迫时其值显著低于对照。(5)相关性分析表明,3个优势物种的P_(n)与F_(v)/F_(m)和F_(v)/F_(o)均呈显著正相关关系,其中猪毛蒿和糙隐子草的P_(n)—F_(v)/F_(m)和P_(n)—F_(v)/F_(o)斜率明显高于胡枝子。研究表明,气候变暖会在一定程度上加剧降水减少对沙质草地3种群落优势物种光合作用的抑制。     

Breakdown of self-incompatibility in a natural population of Petunia axillaris (Solanaceae) in Uruguay containing both self-incompatible and self-compatible plants

 Many members of the Solanaceae display a type of gametophytic self-incompatibility which is controlled by a single multiallelic locus, called the S-locus. From our previous survey of more than 100 natural populations of Petunia axillaris (a solanaceous species) in Uruguay, we had found that the majority of the populations of subspecies axillaris were comprised of virtually all self-incompatible individuals. The rest were ”mixed populations” which contained mostly self-incompatible and some self-compatible individuals. In this study, we examined the self-incompatibility behavior and determined the S-genotypes of 33 plants raised from seeds obtained from one such mixed population, designated U1. We found that 30 of the 33 plants (designated U1–1 through U1–33) were self-incompatible and a total of 18 different S-alleles were represented. To determine the S-genotypes of the three self-compatible plants (U1–2, U1–16, and U1–22) and the possible causes for the breakdown of their self-incompatibility, we carried out reciprocal crosses between each of them and each of the 18 S-homozygotes (S ₁ S ₁ through S ₁₈ S ₁₈ ) obtained from bud-selfed progeny of 14 of the 30 self-incompatible plants. For U1–2 and U1–16, we also carried out additional crosses with U1–25 (with S ₁ S ₁₃ genotype) and an S ₁₃ S ₁₅ plant (obtained from a cross between an S ₁₃ -homozygote and an S ₁₅ -homozygote), respectively. Based on all the pollination results and analysis of the production of S-RNases, products of S-alleles in the pistil, we determined the S-genotypes of U1–2, U1–16, and U1–22, and propose that the breakdown of self-incompatibility in these three plants is caused by suppression of the production of S₁₃-RNase from the S ₁₃ -allele they all carry. We have termed this phenomenon ”stylar-part suppression of an S-allele” or SPS. Received: 25 September 1998 / Revision accepted: 22 December 1998     

Electron and proton transfer in the <Emphasis Type="Italic">ba</Emphasis><Subscript>3</Subscript> oxidase from <Emphasis Type="Italic">Thermus thermophilus</Emphasis>

The ba ₃-type cytochrome c oxidase from Thermus thermophilus is phylogenetically very distant from the aa ₃–type cytochrome c oxidases. Nevertheless, both types of oxidases have the same number of redox-active metal sites and the reduction of O₂ to water is catalysed at a haem a ₃-Cu_B catalytic site. The three-dimensional structure of the ba ₃ oxidase reveals three possible proton-conducting pathways showing very low homology compared to those of the mitochondrial, Rhodobacter sphaeroides and Paracoccus denitrificans aa ₃ oxidases. In this study we investigated the oxidative part of the catalytic cycle of the ba ₃ -cytochrome c oxidase using the flow-flash method. After flash-induced dissociation of CO from the fully reduced enzyme in the presence of oxygen we observed rapid oxidation of cytochrome b (k ≅ 6.8 × 10⁴ s⁻¹) and formation of the peroxy (P_R) intermediate. In the next step a proton was taken up from solution with a rate constant of ~1.7 × 10⁴ s⁻¹, associated with formation of the ferryl (F) intermediate, simultaneous with transient reduction of haem b. Finally, the enzyme was oxidized with a rate constant of ~1,100 s⁻¹, accompanied by additional proton uptake. The total proton uptake stoichiometry in the oxidative part of the catalytic cycle was ~1.5 protons per enzyme molecule. The results support the earlier proposal that the P_R and F intermediate spectra are similar (Siletsky et al. Biochim Biophys Acta 1767:138, 2007) and show that even though the architecture of the proton-conducting pathways is different in the ba ₃ oxidases, the proton-uptake reactions occur over the same time scales as in the aa ₃-type oxidases. Smirnova and Zaslavsky contributed equally to the work described in this paper.     

ON THE VARIABILITY OF CRITICAL ILLUMINATION FOR FLICKER FUSION AND INTENSITY DISCRIMINATION

From the data of experiments with bees in which threshold response is employed as a means of recognizing visual discrimination between stripes of equal width alternately illuminated by intensities I ₁ and I ₂, it is shown that the detectable increment of intensity ΔI, where ΔI = I ₂ - I ₁, is directly proportional to σ_I2 (I ₁ being fixed). From tests of visual acuity, where I ₁ = 0 and the width of the stripes is varied, σ_I2 = kI ₂ + const.; here I ₂ = ΔI, and ΔI/I ₂ = 1. When the visual excitability of the bee is changed by dark adaptation, λI ≡ kΔI (= k'' σ_ΔI) = k'''' I + const. For the measurements of critical illumination at threshold response to flicker, σ_I2 (= σ_ΔI) = k I ₂ = k'' ΔI + const. The data for critical illumination producing threshold response to flicker in the sun-fish Lepomis show for the rods σ_I2 = K I ₂ for the cones σ_I2 = K''(I ₂ + const.). The data thus indicate that in all these experiments essentially the same visual function is being examined, and that the recognition of the production of a difference in effect by alternately illuminated stripes takes place in such a way that d (ΔI)/d (σ_I2) = const., and that ΔI is directly proportional to I (or "I ₂," depending on the nature of the experiment). It is pointed out that the curve for each of the cases considered can be gotten equally well if mean I or σ_I is plotted as a function of the independent variable involved in the experiment. Certain consequences of these and related facts are important for the treatment of the general problem of intensity discrimination.     

Two new species of <Emphasis Type="Italic">Parspina</Emphasis> Pearse, 1920 (Digenea: Cryptogonimidae) from freshwater fishes (Gymnotiformes) of the Paraná River basin in Argentina

Two new species of the cryptogonimid genus Parspina Pearse, 1920 are described from gymnotiform fishes of the Paraná River basin, P. carapo n. sp. from the banded knifefish Gymnotus carapo Linnaeus and P. virescens n. sp. from the glass knifefish Eigenmannia virescens (Valenciennes). Parspina carapo differs from P. virescens in the number of oral spines (32–39 vs 30–33) and their length (28–47 vs 16–28 μm), the distribution of tegumental spines and their anchorage, the types of sensory papillae on the body surface (three vs two types), the extent of body length posterior to the caeca (5 vs 13% of the total body length), the dimensions of the pars prostatica (52 × 34 vs 24 × 10 μm), and in the absence of a gonotyl (vs presence). Both P. carapo and P. virescens differ from P. bagre Pearse, 1920 and P. argentinensis (Szidat, 1954) in the number of oral spines (20–21 and 21–28 in the latter pair) and their length (28–32 and 35–60 μm), and in total body length. Additionally, the two new species differ from P. argentinensis in the arrangement of the vitelline follicles (one continuous band vs two groups on each side of the body) and in having a smaller pars prostatica (149 × 49 μm in the latter). Parspina carapo is the fifth intestinal helminth found in G. carapo, and P. virescens is the first found in E. virescens.     

Effects of ATP-sensitive Potassium Channel Regulators on Chloride Channels in the Sarcoplasmic Reticulum Vesicles from Rabbit Skeletal Muscle

The lipid bilayer technique was used to examine the effects of the ATP-sensitive K⁺ channel inhibitor (glibenclamide) and openers (diazoxide, minoxidil and cromakalim) and Cl⁻ channel activators (GABA and diazepam) on two types of chloride channels in the sarcoplasmic reticulum (SR) from rabbit skeletal muscle. Neither diazepam at 100 μm nor GABA at 150 μm had any significant effect on the conductance and kinetics of the 75 pS small chloride (SCl) channel. Unlike the 150 pS channel, the SCl channel is sensitive to cytoplasmic glibenclamide with K _i ∼ 30 μm. Glibenclamide induced reversible decline in the values of current (maximal current amplitude, I _max and average mean current, I′) and kinetic parameters (frequency of opening F _o , probability of the channel being open P _o and mean open time, T _o , of the SCl channel. Glibenclamide increased mean closed time, T _c , and was a more potent blocker from the cytoplasmic side (cis) than from the luminal side (trans) of the channel. Diazoxide increased I′, P _o , and T _o in the absence of ATP and Mg²⁺ but it had no effect on I _max and also failed to activate or remove the glibenclamide- and ATP-induced inhibition of the SCl channel. Minoxidil induced a transient increase in I′ followed by an inhibition of I _max, whereas cromakalim reduced P _o and I′ by increasing channel transitions to the closed state and reducing T _o without affecting I _max. The presence of diazoxide, minoxidil or cromakalim on the cytoplasmic side of the channel did not prevent [ATP] _cis or [glibenclamide] _cis from blocking the channel. The data suggest that the action(s) of these drugs are not due to their effects on the phosphorylation of the channel protein. The glibenclamide- and cromakalim-induced effects on the SCl channel are mediated via a ``flicker' type block mechanism. Modulation of the SCl channel by [diazoxide] _cis and [glibenclamide] _cis highlights the therapeutic potential of these drugs in regulating the Ca²⁺-counter current through this channel. Received: 2 September 1997/Revised: 20 March 1998     

Generalization of the QST framework in hierarchically structured populations: Impacts of inbreeding and dominance

Q_ST is a differentiation parameter based on the decomposition of the genetic variance of a trait. In the case of additive inheritance and absence of selection, it is analogous to the genic differentiation measured on individual loci, F_ST. Thus, Q_ST?F_ST comparison is used to infer selection: selective divergence when Q_ST > F_ST, or convergence when Q_ST < F_ST. The definition of Q‐statistics was extended to two‐level hierarchical population structures with Hardy–Weinberg equilibrium. Here, we generalize the Q‐statistics framework to any hierarchical population structure. First, we developed the analytical definition of hierarchical Q‐statistics for populations not at Hardy–Weinberg equilibrium. We show that the Q‐statistics values obtained with the Hardy–Weinberg definition are lower than their corresponding F‐statistics when F_IS > 0 (higher when F_IS < 0). Then, we used an island model simulation approach to investigate the impact of inbreeding and dominance on the Q_ST?F_ST framework in a hierarchical population structure. We show that, while differentiation at the lower hierarchical level (Q_SR) is a monotonic function of migration, differentiation at the upper level (Q_RT) is not. In the case of additive inheritance, we show that inbreeding inflates the variance of Q_RT, which can increase the frequency of Q_RT > F_RT cases. We also show that dominance drastically reduces Q‐statistics below F‐statistics for any level of the hierarchy. Therefore, high values of Q‐statistics are good indicators of selection, but low values are not in the case of dominance.     

Preferential solvation of methylmercurated calf thymus deoxyribonucleic acid.

The changes in polymer-solvent interactions that occur when native calf thymus DNA is dialyzed against Na₂SO₄ solutions of a given ionic strength and buffer concentration but of varying concentrations in methylmercuric hydroxide have been investigated with the help of solution density measurements at 25 °C and pH 6.8–7.0. From measurements executed under equilibrium dialysis conditions at the three salt levels 5 mm, 0.05 m, and 0.5 m Na₂SO₄ (m refers to molality) and in the presence of 5 mm cacodylic acid buffer, the density increments $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ for native calf thymus DNA were determined as a function of CH₃HgOH concentration. $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ was found not to vary with organomercurial concentration, irrespective of the concentration of supporting electrolyte, until a certain CH₃HgOH concentration level has been reached, viz., , beyond which $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ increases strongly with increasing concentration of CH₃HgOH. As is shown by optical melting, $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ becomes a function of organomercurial concentration the moment DNA undergoes denaturation brought about by the complexing of CH₃HgOH with the various N-binding sites of the base residues in the DNA double helix.Polymer-solvent interactions, expressed in terms of preferential water interactions (“net hydration”) and preferential salt interactions (“salt solvation”), were derived from the $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ data in combination with data obtained on the preferential interaction of CH₃HgOH with denatured DNA and data on the partial specific volumes of all major solution components, gathered from density measurements on solutions with fixed concentrations of diffusible components. Evidence is presented which shows that denaturation in general decreases the net hydration while salt becomes preferentially associated with the polyelectrolyte. This process is further amplified by the interaction of CH₃HgOH with denatured DNA: Methylmercurated DNA alters the redistribution of diffusible components at dialysis equilibrium to such an extent that in a formal sense large amounts of water are rejected from the immediate vicinity of the polymer. The molecular implications of these findings are explored. The results are further discussed in the light of previous findings where the methylmercury-induced denaturation of DNA had been studied with the help of buoyant density measurements in a Cs₂SO₄ density gradient and by velocity-sedimentation in a variety of sulfate media.