Temporal and spatial distribution of biogenic silica and its significance in the Wuliangsuhai Lake and Daihai Lake

In this work, the concentrations, temporal and spatial distributions and the relationship between biogenic silica (BSi) and primary productivity are discussed on the basis of the geochemistry character of BSi in the water–sediment system of the Wuliangsuhai Lake and Daihai Lake. The results show that the average concentrations of SiO₃^2- and BSi are 3.0 mg/L and 3.5 mg/g in the overlying water and sediments from the Wuliangsuhai Lake, respectively, while they are 1.0 mg/L and 7.5 mg/g, respectively, in the Daihai Lake. It is the uptake and assimilation of diatom phytoplankton which results in the significant difference of the SiO₃^2- concentrations between the two lakes, and the inputs of surface runoff is one of the important factors in impacting the spatial distributions of SiO₃^2- in the overlying water. The spatial distributions of BSi suggest the Si source of the two lakes and indicate the differences of eutrophication types and ancient primary producer between the two lakes. The eutrophication precesses and ancient primary productivity of diatom phytoplankton are reconstructed by applying the geochemistry information of BSi archived in the vertical concentration profiles in the two lake sediments. The geochemistry information of BSi well responds to the paleoenvironment and paleoclimate of the Daihai drainage basin indicating silicate limitation of primary productivity by diatoms phytoplankton in the Daihai Lake.     

Temporal and spatial distribution of biogenic silica and its significance in the Wuliangsuhai Lake and Daihai Lake

In this work, the concentrations, temporal and spatial distributions and the relationship between biogenic silica (BSi) and primary productivity are discussed on the basis of the geochemistry character of BSi in the water–sediment system of the Wuliangsuhai Lake and Daihai Lake. The results show that the average concentrations of SiO₃^2- and BSi are 3.0 mg/L and 3.5 mg/g in the overlying water and sediments from the Wuliangsuhai Lake, respectively, while they are 1.0 mg/L and 7.5 mg/g, respectively, in the Daihai Lake. It is the uptake and assimilation of diatom phytoplankton which results in the significant difference of the SiO₃^2- concentrations between the two lakes, and the inputs of surface runoff is one of the important factors in impacting the spatial distributions of SiO₃^2- in the overlying water. The spatial distributions of BSi suggest the Si source of the two lakes and indicate the differences of eutrophication types and ancient primary producer between the two lakes. The eutrophication precesses and ancient primary productivity of diatom phytoplankton are reconstructed by applying the geochemistry information of BSi archived in the vertical concentration profiles in the two lake sediments. The geochemistry information of BSi well responds to the paleoenvironment and paleoclimate of the Daihai drainage basin indicating silicate limitation of primary productivity by diatoms phytoplankton in the Daihai Lake.     

Gradient of photosynthetic pigments in the bark and leaves of lilac (Syringa vulgaris L.)

The concentration of chlorophyll and a carotenoids in the bark of stems of different age and in the leaves of lilac (Syringa vulgaris L.) was determined. The thickness of bark changes with the age of the stems, ranging from 0.73 mm in the current-year stems to 1.22 mm in 3-year-old ones. Chlorophyll and carotenoids were present through the whole thickness of the bark, except the cork. It was found that chlorophyll and carotenoids are located mainly in the outer layer of the bark, immediately under the cork, to a depth of 400 μm. In this layer the chlorophyll a/b ratio is the highest and the content of chlorophyll is four times larger than that of carotenoids. When penetrating deeper into the bark, the content of chlorophyll and carotenoids as well as the chlorophyll a/b ratio diminishes. Investigations of the leaves showed that most of the chlorophyll is found in the palisade parenchyma, the chlorophyll a/b ratio is the highest in the upper layer. The highest concentration of chlorophyll in the bark is 0.44 mg·dm⁻² and in leaves −1.2 mg⁻²·dm⁻². The highest value of the chlorophyll a/b ratio in the bark is 3.8, and the lowest 0.5, while in the leaves it varies from 4.5 to 3.8 Low values of the chlorophyll a/b ratio are due to the shade conditions existing in the bark and they are evidence of very great differentiation of light conditions within it.     

Soil salt and nutrient concentration in the rhizosphere of desert halophytes

North-West China is an arid region where halophyte plants are rich. Very little is known on the rhizospheric soil of the halophytes in this arid desert region. We conducted a rhizobag experiment on the desert Solonchak soil to investigate the salt and nutrient content in the rhizospheric soil of the desert halophytes. The total salt and the concentrations of 8 major kinds of salt ions increased in the rhizosphere of both succulent halophytes and salt secreting halophytes, but this increase was insignificant for salt-resisting halophytes. Accumulation of Cl^– and Na⁺ is the most significant among the 8 major kinds of salt ions. Accumulation of Cl^– was more significant than that of SO₄^2– in succulent halophytes and salt secreting halophytes. The Na⁺/K⁺, Na⁺/Ca²⁺ and Na⁺/Mg²⁺ ratios in the rhizosphere of all 7 kinds of halophytes were higher than those in the bulk soil. Total N increased significantly in the rhizosphere, but total P and total K decreased. However, the available N, P and K in the rhizosphere of the 7 kinds of halophytes except Phragmites communis Trin. behaved in such an opposite way that available N decreased but available P and available K increased. The ionic contents in the aboveground parts were higher than those in the underground parts of the 7 kinds of halophytes, in particular of both the succulent halophytes and the salt secreting halophytes. Accumulation of Cl^– and Na⁺ in the aboveground parts of the plants was the most significant among that of the 8 major kinds of salt ions.     

Differences between cellular mechanisms of ATP-and noradrenaline-induced inhibition of visceral smooth muscles under conditions of selective and combined activation of M<Subscript>2</Subscript> or M<Subscript>3</Subscript> cholinoreceptors

Our studies of the role of phospholipase C in inhibitory synaptic action upon visceral smooth muscles demonstrated that, under conditions of carbachol (CCh)-induced pre-activation of cholinoreceptors, ATP-or noradrenaline (NA)-evoked relaxation of these muscles is mediated by the phospholipase C-independent pathway, while the phospholipase C-dependent pathway does not manifest itself as a mechanism that determines the inhibitory effect of the above transmitters. Under conditions of pre-activation of muscarinic cholinoreceptors, ATP-and NA-induced relaxation is continued due to activation of inositol trisphosphate (InsP₃)-sensitive receptors despite the fact that the pathway of inhibition is phospholipase C-independent. This is confirmed by complete depression of the inhibitory effects of ATP and NA against the background of CCh-induced contraction after pre-incubation of the studied preparations together with 100 μM 2-APB, a blocker of InsP₃ receptors. Selective blockings of either M₂ or M₃ cholinoreceptors are accompanied by a complete loss of the ability of the above blocker of InsP₃ receptors (2-APB) to suppress ATP-and NA-induced contraction of smooth muscles in the state of CCh-induced contraction. It can be hypothesized that, under conditions of selective pre-activation of M₂ or M₃ cholinoreceptors, the mechanisms of intracellular signalling mediating the inhibition events are modified. The InsP₃-dependent pathway that determines both adrenergic and purinergic inhibition of smooth muscles is switched off, and the inhibitory action of neurotransmitters is realized under such conditions through the InsP₃-independent pathway. Therefore, in our study we first found differences between cellular mechanisms underlying ATP-and NA-induced inhibition of smooth muscles under conditions of selective activation of either M₂ or M₃ cholinoreceptors and the mechanisms underlying the relaxing action of inhibitory neurotransmitters under conditions of combined synergistic activation of cholinoreceptors of both the above-mentioned subtypes. Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 22–31, January–February, 2007.     

Glycine origin of the methyl substituent on C7′-N of octodiose for the biosynthesis of apramycin

Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonine, to the Streptomyces tenebrabrius UD2 fermentation medium substantially increases the production of apramycin with little effect on the growth of mycelia, indicat-ing that glycine and/or serine might be involved in the biosynthesis of apramycin. The ¹³C-NMR analysis of [2-¹³C] glycine-fed (25% enrichment) apramycin showed that glycine specifically and efficiently incorporated into the only N-CH₃ substituent of apramycin on the C7′ of the octodiose moiety. We noticed that the in vivo concentration of S-adenosyl methionine increased in parallel with the addition of glycine, while the addition of methione in the fermentation medium significantly decreased the productivity of apramycin. Therefore, the methyl donor function of glycine is proposed to be involved in the methionine cycle but methionine itself was proposed to inhibit the methylation and methyl transfer processes as previously reported for the case of rapamycin. The ¹⁵N NMR spectra of [2-¹³C,¹⁵N]serine labeled apramycin indicated that serine may also act as a limiting precursor contributing to the ―NH₂ substituents of apramycin.     

Modified micro suction cup/rhizobox approach for the in-situ detection of organic acids in rhizosphere soil solution

Root–soil interactions can strongly influence the soil solution chemistry in the rhizosphere. In the present study we propose a modification of the classical rhizobox/micro suction cup system to make it suitable for the collection and analysis of organic acids in the rhizosphere. In order to show the potential of the method, we tested the modified system with Lupinus albus L. as a model plant known to exude large amounts of citrate. The suction cups were installed through the transparent front plate of the rhizoboxes just after the emergence of cluster roots in order to allow optimal localized collection of soil solution. A small dead-volume allowed almost immediate stabilisation with formaldehyde of the sampled soil solutions in the collection container to prevent microbial degradation. The concentrations of organic acids were significantly larger in the rhizosphere soil solution of active cluster roots of Lupinus albus L. than in the bulk soil solution (about 400 μM of citrate versus <0.05 μM). We were able to follow the exudation process in-situ, which occurred during 2–3 days. Also the concentrations of other organic acids and inorganic anions differed between the bulk soil and the rhizosphere of cluster roots, normal roots, and nodules.     

Effect of mammogenic hormones on the expression of dFGF7, FGF10 and their receptor in mouse mammary gland

To investigate the regulation of estrogen, progesterone and prolactin stimulating the development of mammary gland, the Kunming mice were used as experimental animals in this study.Through the ex-periment in vitro, the effect of mammogenic hormones were systematically investigated on expression of FGF7 and FGF10 and their receptor in different periods.The results are as follows:in mammary glands of mice, 17 beta-estradiol increased the expression of FGF7;progesterone did not affect the expression of FGF7;prolactin up-regulated the expression of FGF7 significantly in pregnancy and lac-tation.17 beta-estradiol increased the expression of FGF10;progesterone and prolactin reduced the expression of FGF10 significantly in virgin;prolactin significantly increased the expression of FGF10 in pregnancy.When 17 beta-estradiol in the body was in relatively high proportion, it would lower the ex-pression of KGFR;while 17 beta-estradiol in the body was in relatively low proportion, it would increase the expression of KGFR.Low concentration of progesterone increased the expression of KGFR and high progesterone did not affect the expression of KGFR.Prolactin increased the expression of KGFR significantly in pregnancy and lactation.     

Adaptation of the photosynthetic apparatus of Nitellopsis obtusa to changing light intensity at the molecular level: different pathways of a singlet excitation quenching

The effect of prolonged illumination (60 min) with photosynthetically active monochromatic radiation of low intensity (3 μmol m⁻² s⁻¹) and high intensity (60 μmol m⁻² s⁻¹), corresponding to the physiological conditions and light stress conditions, respectively, was studied in the algae Nitellopsis obtusa. Illumination of Nitellopsis obtusa cells with strong light was associated with activation of the xanthophyll cycle, manifested by the deepoxidation of violaxanthin and accumulation of antheraxanthin and zeaxanthin. At the same time, the efficient singlet excitation quenching in the photosynthetic apparatus was activated, as demonstrated by the decrease in the intensity of the chlorophyll a fluorescence emission by ca 50 %. The difference of the fluorescence excitation spectra recorded before and after the light treatment match the difference absorption spectrum of the xanthophyll cycle pigments. The illumination with low light intensity resulted also in the chlorophyll a fluorescence quenching but the effect was very small (less than 10 %). The fluorescence quenching is interpreted in terms of the energy transfer between the Q_y energy level of chlorophyll a and the 2¹ A_g ⁻ energy level of zeaxanthin. The singlet energy levels of carotenoids, corresponding to the green spectral region, are also taken into consideration in the interpretation of the excitation energy exchange between the carotenoids and chlorophylls. Possible molecular mechanisms involved in the activation of the strong and the weak excitation quenching, including violaxanthin isomerization, and possible physiological functions of such pathways of energy transfer are discussed.     

Refined structure of basic phospholipase A2 from venom of Agkistrodon halys Pallas in orthorhombic crystal form I at 0.25 nm resolution

The basic phospholipase A2 from the venom of Agkistrodon halys Pallas is a potent hemolytic toxin and anticoagulant. The accurate rotation and translation parameters of the molecules in orthorhombic crystal form I were successfully obtained using the fitting refinement technique. The structure was refined in the resolution range of 0. 6-0.25 nm using least square refinement with non-crystallographic two fold symmetry restraint, and resulted in the final R factor of 20.1 % , and the rms deviations from ideal stereochemistry were 0. 001 3 nm for bond lengths and 1. 32° for bond angles. The overall architecture of the present structure was similar to that of the determined structure of the orthorhombic crystal form Ⅱ, with a few differences in the regions of the β-wing and Ca²⁺-binding loop. The dimers formed by the two molecules in the asymmetric unit in both crystal forms were also similar. However, one of the monomers showed an orientational difference of 5.5° along the dimer interface in the two crystal forms, suggesting the flexibility of the interface of the dimer to some degree. The molecular packing of the dimer in crystal form I was much more compact than that in crystal form Ⅱ.     

Effects of La3+ on the competence of Escherichia coli as studied by microcalorimetry

A series of microcalorimetric experiments were performed to investigate the effect of La³⁺ on the formation of the competent state of Escherichia coli HB101 by using a LKB-2277 BioActivity Monitor at 37°C. The thermogenic curves in the absence and in the presence of La³⁺ were obtained. Based on these curves, we calculated that the total heat effects (Q _T) and the maximal power (P _max) in the presence and absence of La³⁺. Our experiments indicate that the total heat effects in the presence of a low concentration of La³⁺ (≤ 100 μg/mL) are greater than those in the absence of La³⁺. Their trends are similar with respect to the increasing concentration of La³⁺. To the contrary, when the concentration of La³⁺ is greater than 100 μg/mL, the total heat effects decrease with the increasing concentration of La³⁺. Therefore, in the latter case, La³⁺ has inhibitory effects on the formation of competence. Our experimental results suggest that the La³⁺ ion in the environmental ecosystem can facilitate the formation of competence of E. coli HB101 and further stimulate the transfer of genetic materials between organisms.     

Determination of Mercury and Methylmercury in Hair of the Czech Children’s Population

The developed method for mercury speciation analysis has been validated and used for the biomonitoring study of mercury species in human hair. Statistical evaluation proved the reliability of simplified determination of inorganic mercury (difference between total mercury and methylmercury). The results of the validation showed that the method is very well suitable for the determination of both species of mercury in hair for biomonitoring purposes. Non-exposed schoolchildren from three areas in the western and central part of the Czech Republic were chosen as the target group. Tenth of a microgram per gram of the total mercury were generally found in the analyzed hair; values higher than 1 μg g⁻¹ were detected only exceptionally. Comparable results were obtained for two western areas and differed significantly from those for the third area located in the central part of the Czech Republic. In the areas examined, the mean methylmercury contents amounted to 23–46% of the total mercury in the hair. The results confirm an assumption that exposure to mercury does not pose a significant risk to the population in the Czech Republic.     

On the relationship between the number of negative slope regions in the voltage-current curve of the Hodgkin-Huxley model and its parameter values

 We consider the problem of the existence of a negative slope region (NSR) in the voltage-current curve of the neuronal membrane and the relationship between this phenomenon and the membrane parameters. For the Hodgkin-Huxley model it is proposed to determine the dependence of the number of NSR on the values of the maximal sodium (gˉ_Na) and potassium (gˉ_K) conductances. The method is suggested for constructing the boundaries on the (gˉ_Na, gˉ_K) plane, in passing through which the number of NSR changes to 1. Using the method we partition the (gˉ_Na, gˉ_K) plane into the regions corresponding to the curves with the different number of NSR. This number can be changed from 0 to 2 in changing the values of gˉ_Na and gˉ_K over the physiologically possible range. Received: 9 December 1993/Accepted in revised form: 10 February 1995     

Microscopic and semimacroscopic redox calculations: what can and cannot be learned from continuum models

 The major role of electrostatic effects in the control of redox potentials in proteins is now widely appreciated. However, the evaluation and conceptualization of the actual electrostatic contributions is far from trivial, and some models still overlook the nature of electrostatic effects in proteins. This commentary considers different contributions to redox potentials of proteins and discusses the ability of different models to capture these contributions. It is pointed out that macroscopic models which consider the protein as a medium of uniform low dielectric constant cannot reproduce the proper physics of redox proteins. In particular, it is pointed out that the crucial effects of the protein permanent dipoles must be taken into account explicitly and that these permanent dipoles involve effective dielectric constants that are different from those for ionized residues. It is also argued that the reorganization of the protein upon change of oxidation states or ionization of protein residues should be taken into account in redox calculations. The role of water penetration and the inadequacy of describing electrostatic effects by solvent accessibility is briefly mentioned. The nature and the meaning of the "dielectric constant" that should be used in redox calculations are also discussed. It is pointed out that the "dielectric constant" ε_p used in current discretized continuum (DC) models is simply a representation of the contributions which are treated implicitly and not the proper dielectric constant of the protein. It is then explained that the need to use a large "dielectric constant" in DC models reflects, among other factors, the implicit representation of the reorganization of permanent dipoles, and that even an explicit treatment of the fluctuations of ionized surface residues will lead to incorrect results when one uses ε_p=εˉ in continuum treatments. Finally, it is suggested that although the discussion and classification of different contributions to redox potentials is very useful, only the evaluation of the totality of the protein contributions (rather than an arbitrary subset) can lead to a quantitative understanding of redox proteins. Received, accepted: 26 November 1996     

Cell cycle reactivation in cultured pea embryo axes. Effect of abscisic acid

Summary We used cultured pea embryo axes to study the effect of exogenous abscisic acid (ABA) on the reactivation of cell proliferation at germination. ABA (100 μM) was administered in a complete medium or in a medium without KNO₃ (the main source of K⁺ in the complete medium). In the presence of ABA, only a few meristematic root tip nuclei progressed through the cell cycle during the first 24 h of germination. Compared to the control the percentage of G₀/G₁ cells remained high. In the absence of KNO₃, the inhibitory effect of ABA on the cell cycle increased and the transition from G₁ to S was almost completely inhibited after 24 h of germination. Moreover, the amount of a 47 kDa nuclear protein remained high in embryos treated with ABA whereas it decreased in the control.     

The effect of paclobutrazol on in vitro rooting and growth of GF-677 hybrid peach rootstock

This paper deals with the evaluation of the influence of paclobutrazol (N-dimethylaminosuccinamic acid) and 2-naphtoxyacetic acid on rooting and growth of GF-677 hybrid peach rootstocks. The influence of these substances on the average number of roots per plant, the average length of roots per plant and the height of plants was evaluated as well as the effect of the addition of paclobutrazol before and after media sterilisation. As the obtained results indicate, plants, which were rooted on media with paclobutrazol and without auxin had the lowest number of roots per plant. Paclobutrazol showed a statistically significant negative effect on both the length of roots and the height of plants. It canbe concluded that, for the rooting of GF-677 rootstock it is helpful to use auxin plus paclobutrazol in concentration 0.43 μM. Higher concentrations affect inhibition, mainly in height of plants 14 days after transplant to soil. A part of the results referring to the influence of PP 333 on numbers of roots was presented at the conference “Recent Advances in Plant Biotechnology, 5th International symposium in the series”, Stará Lesná, Slovakia, 7–13 September, 2003.     

Store-Dependent Entry of Ca<Superscript>2+</Superscript> into Sensory Neurons of the Rat

We studied store-dependent (activated by depletion of the endoplasmic reticulum, ER, store) entry of Ca²⁺ from the extracellular medium into neurons of the rat spinal ganglia (small- and medium-sized cells; diameter, 18 to 36 μm). Activation of ryanodine-sensitive receptors of the ER in the studied neurons superfused by Tyrode solutions containing Ca²⁺ or with no Ca²⁺ was provided by application of 10 mM caffeine. The decay phase of caffeine-induced calcium transients in a Ca²⁺-containing solution was significantly longer than that in a Ca²⁺-free solution. This fact allows us to suppose that such a phenomenon is determined by Ca²⁺ entry into the neuron from the extracellular medium activated by caffeine-induced depletion of the ER store. Substitution of Ca²⁺-free extracellular solution by Ca²⁺-containing Tyrode solution, after depletion of the ER stores induced by applications of 100 nM ryanodine, 200 μM ATP, or 1 μM thapsigargin, resulted in increases in the concentration of intracellular Ca²⁺. These observations allow us to postulate that store-dependent Ca²⁺ entry into the studied neurons is activated after depletion not only of the inositol trisphosphate-sensitive ER store but also of the ryanodine-sensitive store. This entry also occurs after blocking of ATPases of the ER by thapsigargin. The kinetic characteristics of the rising phase of store-dependent Ca²⁺ entry induced by depletion of the ER stores under the influence of various agents are dissimilar; this can be related to different mechanisms of activation of such signals and/or to a compartmental organization of the ER. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 277–283, May–June, 2005.     

Negative inotropic response to cerium in ventricular papillary muscle is mediated by reactive oxygen species

This study was performed with the objective of assessing the mechanical response of the myocardium to different levels of cerium and delineation of the mechanism underlying the mediation of the functional changes. Rat ventricular papillary muscle was used as the experimental model. Isolated papillary muscles were exposed to different concentrations of CeCl₃ and the force of contraction was measured using a force transducer. Experiments have revealed that the negative inotropic response to CeCl₃ was proportional to its concentration. The inotropic changes were found to be completely reversible at concentrations ≤5μM, and partially reversible at higher concentrations. Neutralization of cerium-induced inotropic changes by the superoxide anion scavenger superoxide dismutase (SOD) at concentrations ≤5 μM indicates that the mechanical changes are mediated by reactive oxygen species. At higher concentrations of Ce³⁺, SOD partially reversed the contractile changes. The beneficial effect of SOD was seen only if the muscles were pretreated with the scavenger prior to the addition of cerium chloride.     

Role of protein kinase C in growth stimulation of primary mouse colonic epithelial cells

Summary The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (160 nM) and the secondary bile acid, deoxycholic acid (50 μM) stimulated DNA synthesis in quiescent primary epithelial cells from the normal mouse colon as measured by autoradiographic analysis of [³H]thymidine incorporation. The purpose of the present study was to investigate the involvement of protein kinase C in the proliferative response of the normal colonic cells. The protein kinase C inhibitor, bisindolylmaleimide GF 109203X, efficiently blocked the proliferative response of the cells to the phorbol ester and caused a dose-dependent decrease in the response to deoxycholic acid. While the phorbol ester-induced proliferation was unaffected by another inhibitor, H-7, the response of the cells to deoxycholic acid was blocked. Pretreatment of the cells with the phorbol ester (160 nM) for 24 h blocked the proliferative response to deoxycholic acid. Measurement of the intracellular distribution of protein kinase C activity showed a time-dependent and significant translocation of the enzyme activity from the soluble to the particulate cell fractions after exposure to 12-O-tetradecanoylphorbol-13-acetate. While exposure to the bile acid indicated a similar time-dependent translocation of the enzyme activity, the effect was not significant. The phorbol ester induced a time-dependent accumulation of c-fos mRNA and protein as measured by solution hybridization and immunocytochemistry, respectively. No effect of deoxycholic acid on c-fos expression could be observed in the present study. The data support a role for protein kinase C in the growth stimulating effect of physiological concentrations of deoxycholic acid on normal colonic epithelial cells. However, differences in the mechanisms underlying phorbol ester- and bile acid-induced proliferation are indicated.