On the conformational dependence of the proton chemical shifts in nucleosides and nucleotides. I. Proton shifts in the ribose ring of pyrimidine nucleosides as a function of the torsion angle about the glycosyl bond

Molecular orbital computations are performed on the different contributions to the variation of the chemical shifts of the non-exchangeable protons of the ribose ring in pyrimidine nucleosides as a function of the torsion angle X_CN about the glycosyl bond. They show that the ring current effects are negligible, that the contribution of the atomic diamagnetic anisotropy is important for protons which come at very short distances to the anisotropic group (C₂ = 0₂) and that the polarization effect may have a determining influence on the sign of the variation of the chemical shift. The theoretical results are discussed in relation to the experimental findings on the differences between the chemical shifts of the ribose protons of pyrimidine nucleosides methylated at C₅ and C₆.     

A multipurpose CT-guided stereotactic instrument of simple design

The instrument is based upon a radiolucent ring fixed to the skull by four pins. This locks into a frame for CT scanning from which the x, y and z stereotactic coordinates are derived. The head ring may be locked into a compatible support on the operating table for biopsy. A similar support and localization system is used for rotational radiotherapy. With the current 14 MeV apparatus, fields as small as 2 cm in diameter are available with 90% dosage fall-off in the surrounding 1-cm shell.     

Determinants of mountain birch growth in situ: effects of temperature and herbivory

Variation in in situ growth performance of the mountain birch as indicated by the widths of annual rings was analysed and related mainly to temperature and herbivory using ring width series from five heath forest sites in the Lake Torneträsk area, northern Sweden. Climate explained 48–64% of the variation in age-corrected mean ring width series. In general, the effect of current year July followed by June temperature was most important at all sites. A warm May resulted in wider rings due to an earlier budburst. Short-term (inter-annual) responses to increased temperature were in most cases not reflected into long-term responses (decades). A large proportion of the variation in stem mean ring width was due to variation among stems within trees (81%) in these polycormic trees, while variation among sites was marginal (0.4%). Within trees, main stems grew faster and were more responsive to climate variation than subordinate stems. No effect of insect herbivory on ring width was found at low defoliation levels (≤12%). At a defoliation level of ca 84% a one-year reduction in stem growth was observed while the growth reduction (ca 50% reduction in ring width) lasted for 4 yr after ca 93% defoliation. After outbreaks resulting in complete defoliation and some stem mortality, ring widths of surviving stems mainly responded with increased growth. Basal sprouts, emerging just after a severe insect outbreak with a high mortality of old stems, grew faster than sprouts occurring during other periods. It is concluded that the mountain birch is well adapted to recover from Epirrita outbreaks; the ability to produce basal sprouts, that can benefit from an existing root system for fast initial growth, is one important mechanism for this.     

Branching exponent heterogeneity and wall shear stress distribution in vascular trees

A bifurcating arterial system with Poiseuille flow can function at minimum cost and with uniform wall shear stress if the branching exponent (z) = 3 [where z is defined by (D(1))(z) = (D(2))(z) + (D(3))(z); D(1) is the parent vessel diameter and D(2) and D(3) are the two daughter vessel diameters at a bifurcation]. Because wall shear stress is a physiologically transducible force, shear stress-dependent control over vessel diameter would appear to provide a means for preserving this optimal structure through maintenance of uniform shear stress. A mean z of 3 has been considered confirmation of such a control mechanism. The objective of the present study was to evaluate the consequences of a heterogeneous distribution of z values about the mean with regard to this uniform shear stress hypothesis. Simulations were carried out on model structures otherwise conforming to the criteria consistent with uniform shear stress when z = 3 but with varying distributions of z. The result was that when there was significant heterogeneity in z approaching that found in a real arterial tree, the coefficient of variation in shear stress was comparable to the coefficient of variation in z and nearly independent of the mean value of z. A systematic increase in mean shear stress with decreasing vessel diameter was one component of the variation in shear stress even when the mean z = 3. The conclusion is that the influence of shear stress in determining vessel diameters is not, per se, manifested in a mean value of z. In a vascular tree having a heterogeneous distribution in z values, a particular mean value of z (e.g., z = 3) apparently has little bearing on the uniform shear stress hypothesis.     

Analysis of the principal g-tensors in single crystals of ferrimyoglobin complexes

This paper describes a method of determining the directions of the principal axes of the g-tensors in single crystals from measurements of the g-value variation in three crystalline planes (ab, bc*, ac) and of the principal values of g-tensors. Measurements of paramagnetic resonance spectra of ferrimyoglobin (Mb(Fe3+)) complexes (Mb(Fe3+).CN-, .N3-, .imidazole(Im.) and .OCN-) in single crystals provided detailed information on the electronic state of the Fe3+. The direction of the z axis in Mb(Fe3+).CN-, .N3- and .Im. is not parallel to that in Mb(Fe3+).H2O, which has been used as the haem normal, where the z axis is one of the principal axes of the g-tensors corresponding to the maximal (in low-spin state of Fe3+ in haem) or minimal (in high-spin state of Fe3+ in haem) g-value. In Mb(Fe3+).OCN-, however, which is in thermal equilibrium between high-spin and low-spin states, the directions of the z axis in both states seem to be perpendicular to the haem plane. The direction of the x axis is not parallel to the plane of the linked histidine ring.     

Ring current effects in the conformation dependent NMR chemical shifts of aliphatic protons in the basic pancreatic trypsin inhibitor.

Previously, a highly refined crystal structure and energy refined atomic coordinates were obtained for the basic pancreatic trypsin inhibitor, as well as numerous individual resonance assignments in the 1H NMR spectrum. These data were now used to investigate the contributions from the local ring current fields of the aromatic rings to the overall conformation dependent chemical shifts in this globular protein. A program was written which allowed the consideration of certain aspects of internal mobility of the protein, and the different commonly used ring current equa tions were compared. These studies indicate that ring current shifts are the dominant contribution to the observed conformation dependent chemical shifts of the peripheral aliphatic side chain protons. On the other hand, it appears that ring current shifts do not make dominant contributions to the conformation dependent shifts of the backbone alpha- and amide protons or the aromatic protons in the inhibitor. On the basis of the empirical calibration with the peripheral aliphatic side chain protons, the Johnson-Bovey ring current equation was selected for an analysis of the ring geometries of two prolines in the inhibitor.     

长白山红松年轮碳同位素与净初级生产力的关系

解析树木年轮碳同位素变化是揭示气候与环境变化的有效途径,然而少有研究分析年轮碳同位素对森林净初级生产力(NPP)的指示效应.基于生长季气象因子,分析了长白山红松年轮δ¹³C记录序列与阔叶红松林红松种群NPP变化趋势以及两者之间的相关关系.结果表明: 1970年以前,研究区红松年轮δ¹³C与红松种群NPP变化同步,且两者间呈极显著线性正相关关系,年轮δ¹³C记录了气候变化对红松种群NPP的影响;1970年以后,红松年轮δ¹³C与红松种群NPP变化出现分异,两者呈负相关关系但相关性不显著,表明干旱等其他环境因子的影响使年轮δ¹³C对气候变化的敏感性和对NPP指示性降低.这一相关关系在红松年轮δ¹³C与当年和下一年红松种群NPP之间都存在,表明当年环境状况对来年红松生长的重要意义.说明长白山红松年轮δ¹³C对红松种群NPP有良好的指示性,树木年轮δ¹³C有重建森林历史NPP长期变化的潜力.     

Inhibition of LDL oxidation by flavonoids in relation to their structure and calculated enthalpy

Twenty flavonoid compounds of five different subclasses were selected, and the relationship of their structure to the inhibition of low-density lipoprotein (LDL) oxidation in vitro was investigated. The most effective inhibitors, by either copper ion or 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH) induction, were flavonols and/or flavonoids with two adjacent hydroxyl groups at ring B. In the presence of the later catechol group, the contribution of the double bond and the carbonyl group at ring C was negligible. Isoflavonoids were more effective inhibitors than other flavonoid subclasses with similar structure. Substituting ring B with hydroxyl group(s) at 2' position resulted in a significantly higher inhibitory effect than by substituting ring A or ring B at other positions. The type of LDL inducer had no effect in flavonoids with catechol structure. Calculated heat of formation data (deltadeltaH(f)) revealed that the donation of a hydrogen atom from position 3 was the most likely result, followed by that of a hydroxyl from ring B. Position 3 was favored only in the presence of conjugated double bonds between ring A to ring B. This study makes it possible to assign the contribution of different functional groups among the flavonoid subclasses to in vitro inhibition of LDL oxidation.     

Differentiation of the anomeric configuration and ring form of glucosyl-glycolaldehyde anions in the gas phase by mass spectrometry: isomeric discrimination between m/z 221 anions derived from disaccharides and chemical synthesis of m/z 221 standards

Mass spectrometry of disaccharides in the negative-ion mode frequently generates product anions of m/z 221. With glucose-containing disaccharides, dissociation of isolated m/z 221 product ions in a Paul trap yielded mass spectra that easily differentiated between both anomeric configurations and ring forms of the ions. These ions were shown to be glucosyl-glycolaldehydes through chemical synthesis of their standards. By labeling the reducing carbonyl oxygen of disaccharides with 18O to mass discriminate between monosaccharides, it was established that the m/z 221 ions are comprised solely of an intact nonreducing sugar with a two-carbon aglycon derived from the reducing sugar, regardless of the disaccharide linkage position. This enabled the anomeric configuration and ring form of the ion to be assigned and the location of the ion to the nonreducing side of a glycosidic linkage to be ascertained. Detailed studies of experimental factors necessary for reproducibility in a Paul trap demonstrated that the unique dissociation patterns that discriminate between the isomeric m/z 221 ions could be obtained from month-to-month in conjunction with an internal energy-input calibrant ion that ensures reproducible energy deposition into isolated m/z 221 ions. In addition, MS/MS fragmentation patterns of disaccharide m/z 341 anions in a Paul trap enabled linkage positions to be assigned, as has been previously reported with other types of mass spectrometers.     

综合性状及其分量的多元条件分析

提出基于混合线性模型的多元条件分析方法,用于分析复杂综合性状的分量对其目标性状的贡献。定义了贡献率和贡献遗传效应两个概念,贡献率测定给定分量性状的遗传变异对目标性状的贡献比率,贡献遗传效应衡量给定分量性状的遗传效应对目标性状的贡献值。运用所提出的新方法分析了棉花籽棉产量的3个分量对产量的贡献。     

A linear plasmid truncation induces unidirectional flagellar phase change in H:z66 positive Salmonella Typhi

The process by which bacteria regulate flagellar expression is known as phase variation and in Salmonella enterica this process permits the expression of one of two flagellin genes, fliC or fljB, at any one time. Salmonella Typhi (S. Typhi) is normally not capable of phase variation of flagellar antigen expression as isolates only harbour the fliC gene (H:d) and lacks an equivalent fljB locus. However, some S. Typhi isolates, exclusively from Indonesia, harbour an fljB equivalent encoded on linear plasmid, pBSSB1 that drives the expression of a novel flagellin named H:z66. H:z66+S. Typhi isolates were stimulated to change flagellar phase and genetically analysed for the mechanism of variation. The phase change was demonstrated to be unidirectional, reverting to expression from the resident chromosomal fliC gene. DNA sequencing demonstrated that pBSSB1 linear DNA was still detectable but that these derivatives had undergone deletion and were lacking fljA(z66) (encoding a flagellar repressor) and fljB(z66). The deletion end-point was found to involve one of the plasmid termini and a palindromic repeat sequence within fljB(z66), distinct to that found at the terminus of pBSSB1. These data demonstrate that, like some Streptomyces linear elements, at least one of the terminal inverted repeats of pBSSB1 is non-essential, but that a palindromic repeat sequence may be necessary for replication.     

Improving the analysis of movement data from marked individuals through explicit estimation of observer heterogeneity

Ring re-encounter data, in particular ring recoveries, have made a large contribution to our understanding of bird movements. However, almost every study based on ring re-encounter data has struggled with the bias caused by unequal observer distribution. Re-encounter probabilities are strongly heterogeneous in space and over time. If this heterogeneity can be measured or at least controlled for, the enormous number of ring re-encounter data collected can be used effectively to answer many questions. Here, we review four different approaches to account for heterogeneity in observer distribution in spatial analyses of ring re-encounter data. The first approach is to measure re-encounter probability directly. We suggest that variation in ring re-encounter probability could be estimated by combining data whose re-encounter probabilities are close to one (radio or satellite telemetry) with data whose re-encounter probabilities are low (ring re-encounter data). The second approach is to measure the spatial variation in re-encounter probabilities using environmental covariates. It should be possible to identify powerful predictors for ring re-encounter probabilities. A third approach consists of the comparison of the actual observations with all possible observations using randomization techniques. We encourage combining such randomisations with ring re-encounter models that we discuss as a fourth approach. Ring re-encounter models are based on the comparison of groups with equal re-encounter probabilities. Together these four approaches could improve our understanding of bird movements considerably. We discuss their advantages and limitations and give directions for future research.     

The Evolution of Plasticity and Nonplastic Spatial and Temporal Adaptations in the Presence of Imperfect Environmental Cues

A model for the evolution of plasticity is considered in which the phenotype, undergoing stabilizing selection, is modeled as a linear function of an environmental cue correlated with the phenotypic optimum, with the coefficients z(0) and z(1) evolving according to standard quantitative genetic theory. In contrast to previous theoretical models, as the rate of migration between demes or the rate of cyclic fluctuations in the optimum increases, the amount of plasticity z&d1;1 at equilibrium is shown to increase gradually, in part accounting for the effect of reduced nonplastic adaptation and reaching a maximum equal to the squared correlation between the environmental cue and the phenotypic optimum. Given that information available to the organism is limited, this bias of the expressed phenotype toward the global optimum is still optimal, however, in a certain decision-theoretic sense. When genetic variation in the plastic component of the trait is small so that spatial or temporal differentiation in plasticity is small, the effect of plasticity on nonplastic adaptation is to reduce the effects of variation in the phenotypic optimum by a factor 1-z&d1;1 only. Information acquisition costs and joint evolution of sensory systems are discussed.     

Liquid chromatographic method for the determination of uridine in human serum

A validated gas chromatography (GC)-mass spectrometric (MS) method for the analysis of hydroxyproline in rat femur is reported. Hydroxyproline in bone hydrolysates was extracted with an anion exchange resin and the N(O)-tert-butyldimethylsilyl derivatives analyzed by GC-MS. The hydroxyproline concentration was estimated relative to pipecolic acid, 3,4-dehydroproline and n-tetracosane as internal standards. The mass-to-charge ratios (m/z) for the ions used for quantitation by single ion monitoring were 314 m/z for hydroxyproline, 198 m/z for pipecolic acid, 256 m/z for dehydroproline and 57 m/z for n-tetracosane. A coefficient of variation of 5.8% was achieved and the limit of detection was calculated to be 0.233 micromol/l bone hydrolysate.     

Evidence for involvement of the phenylpropanoid pathway in the biosynthesis of the norlignan agatharesinol

In order to study the biosynthesis of agatharesinol, a norlignan, l-phenylalanine-[ring-2,3,4,5,6-2H] and trans-cinnamic acid-[ring-13C6] were administered to fresh sapwood sticks of Cryptomeria japonica (sugi, Japanese cedar), that is, the labeled precursors were allowed to be absorbed through the tangential section of the wood sticks. The wood sticks were then maintained in high humidity desiccators for approximately 20 d after which ethyl acetate (EtOAc) extracts of the wood sticks were analyzed by gas chromatography-mass spectrometry (GC-MS). Native agatharesinol (trimethylsilylated) produces an m/z 369 ion and an m/z 484 ion that are characteristic of its structure. Agatharesinol formed in the sapwood sticks treated with the deuterium-labeled l-phenylalanine generated both of these ions together with m/z 373 and 377 ions (m/z 369+4 and +8, respectively), and also m/z 488 and 492 ions (m/z 484+4 and +8, respectively). Generation of m/z 373 and 488 ions is attributed to the substitution by deuterium of the four hydrogen atoms of either of the p-hydroxyphenyl rings of agatharesinol, and that of m/z 377 and 492 ions is attributed to the substitution by deuterium of the eight hydrogen atoms of both p-hydroxyphenyl rings. In the administration of the 13C-labeled trans-cinnamic acid, m/z 375 and 381 ions (m/z 369+6 and +12, respectively), and also m/z 490 and 496 ions (m/z 484+6 and +12, respectively) were found, indicating that either aromatic ring or both aromatic rings of agatharesinol were 13C-labeled. Consequently, assimilation of the labeled precursors into agatharesinol was clearly detected, and an experimental procedure for studies on the biosynthesis was developed.     

Tree growth variation in the tropical forest: understanding effects of temperature,rainfall and CO2

Tropical forest responses to climatic variability have important consequences for global carbon cycling, but are poorly understood. As empirical, correlative studies cannot disentangle the interactive effects of climatic variables on tree growth, we used a tree growth model (IBTREE) to unravel the climate effects on different physiological pathways and in turn on stem growth variation. We parameterized the model for canopy trees of Toona ciliata (Meliaceae) from a Thai monsoon forest and compared predicted and measured variation from a tree‐ring study over a 30‐year period. We used historical climatic variation of minimum and maximum day temperature, precipitation and carbon dioxide (CO₂) in different combinations to estimate the contribution of each climate factor in explaining the inter‐annual variation in stem growth. Running the model with only variation in maximum temperature and rainfall yielded stem growth patterns that explained almost 70% of the observed inter‐annual variation in stem growth. Our results show that maximum temperature had a strong negative effect on the stem growth by increasing respiration, reducing stomatal conductance and thus mitigating a higher transpiration demand, and – to a lesser extent – by directly reducing photosynthesis. Although stem growth was rather weakly sensitive to rain, stem growth variation responded strongly and positively to rainfall variation owing to the strong inter‐annual fluctuations in rainfall. Minimum temperature and atmospheric CO₂ concentration did not significantly contribute to explaining the inter‐annual variation in stem growth. Our innovative approach – combining a simulation model with historical data on tree‐ring growth and climate – allowed disentangling the effects of strongly correlated climate variables on growth through different physiological pathways. Similar studies on different species and in different forest types are needed to further improve our understanding of the sensitivity of tropical tree growth to climatic variability and change.     

Genetically engineered biosynthesis of macrolide derivatives including 4-amino-4,6-dideoxy-L-glucose from Streptomyces venezuelae YJ003-OTBP3

Two sugar biosynthetic cassette plasmids were used to direct the biosynthesis of a deoxyaminosugar. The pOTBP1 plasmid containing TDP-glucose synthase (desIII), TDP-glucose-4,6-dehydratase (desIV), and glycosyltransferase (desVII/desVIII) was constructed and transformed into S. venezuelae YJ003, a strain in which the entire gene cluster of desosamine biosynthesis is deleted. The expression plasmid pOTBP3 containing 4-aminotransferase (gerB) and 3,5-epimerase (orf9) was transformed again into S. venezuelae YJ003- OTBP1 to obtain S. venezuelae YJ003-OTBP3 for the production of 4-amino-4,6-dideoxy-L-glucose derivatives. The crude extracts obtained from S. venezuelae ATCC 15439, S. venezuelae YJ003, and S. venezuelae YJ003-OTBP3 were further analyzed by TLC, bioassay, HPLC, ESI/MS, LC/MS, and MS/MS. The results of our study clearly shows that S. venezuelae YJ003-OTBP3 constructs other new hybrid macrolide derivatives including 4-amino-4,6-dideoxy-L-glycosylated YC-17 (3, [M+ Na+] m/z=464.5), methymycin (4, m/z=480.5), novamethymycin (6, m/z=496.5), and pikromycin (5, m/z=536.5) from a 12- membered ring aglycon (10-deoxymethynolide, 1) and 14-membered ring aglycon (narbonolide, 2). These results suggest a successful engineering of a deoxysugar pathway to generate novel hybrid macrolide derivatives, including deoxyaminosugar.     

The constancy of the G matrix through species divergence and the effects of quantitative genetic constraints on phenotypic evolution: a case study in crickets

Long-term phenotypic evolution can be modeled using the response-to-selection equation of quantitative genetics, which incorporates information about genetic constraints (the G matrix). However, little is known about the evolution of G and about its long-term importance in constraining phenotypic evolution. We first investigated the degree of conservation of the G matrix across three species of crickets and qualitatively compared the pattern of variation of G to the phylogeny of the group. Second, we investigated the effect of G on phenotypic evolution by comparing the direction of greatest quantitative genetic variation within species (g(max)) to the direction of phenotypic divergence between species (Delta(z)). Each species, Gryllus veletis, G. firmus, and G. pennsylvanicus, was reared in the laboratory using a full-sib breeding design to extract quantitative genetic information. Five morphological traits related to size were measured. G matrices were compared using three statistical approaches: the T method, the Flury hierarchy, and the MANOVA method. Results revealed that the differences between matrices were small and mostly caused by differences in the magnitude of the genetic variation, not by differences in principal component structure. This suggested that the G matrix structure of this group of species was preserved, despite significant phenotypic divergence across species. The small observed differences in G matrices across species were qualitatively consistent with genetic distances, whereas ecological information did not provide a good prediction of G matrix variation. The comparison of g(max) and Delta(z) revealed that the angle between these two vectors was small in two of three species comparisons, whereas the larger angle corresponding to the third species comparison was caused in large part by one of the five traits. This suggests that multivariate phenotypic divergence occurred mostly in a direction predicted by the direction of greatest genetic variation, although it was not possible to demonstrate the causal relationship from G to Delta(z). Overall, this study provided some support for the validity of the predictive power of quantitative genetics over evolutionary time scales.     

Effect of gravity on chest wall mechanics.

Chest wall mechanics was studied in four subjects on changing gravity in the craniocaudal direction (G(z)) during parabolic flights. The thorax appears very compliant at 0 G(z): its recoil changes only from -2 to 2 cmH(2)O in the volume range of 30-70% vital capacity (VC). Increasing G(z) from 0 to 1 and 1.8 G(z) progressively shifted the volume-pressure curve of the chest wall to the left and also caused a fivefold exponential decrease in compliance. For lung volume <30% VC, gravity has an inspiratory effect, but this effect is much larger going from 0 to 1 G(z) than from 1 to 1.8 G(z). For a volume from 30 to 70% VC, the effect is inspiratory going from 0 to 1 G(z) but expiratory from 1 to 1.8 G(z). For a volume greater than approximately 70% VC, gravity always has an expiratory effect. The data suggest that the chest wall does not behave as a linear system when exposed to changing gravity, as the effect depends on both chest wall volume and magnitude of G(z).     

Plasticity in Dendroclimatic Response across the Distribution Range of Aleppo Pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.