Carbon density and its spatial distribution in the Potentilla fruticosa dominated alpine shrub in Qinghai,China

Aims Shrub recovery is recognized as an important cause of the increase of carbon stocks in China, and yet there are great uncertainties in the carbon sink capacities of shrubs. Our objectives were to estimate carbon density and its spatial distribution in alpine shrubs.
Methods Eight sites in Potentilla fruticosa dominated shrublands across Qinghai, China were investigated. Plant biomass and carbon content in leaves, branches and stems, and roots were measured to analyze the biomass allocation and carbon density.
Important findings Mean carbon densities in biological carbon, litter, soil and whole ecosystem of P. fruticosa shrublands were 5088.54, 542.1, 35903.76 and 41534.4 kg·hm^-2, respectively. Carbon density in the shrub layer was more than 68% of the biological carbon density of the whole ecosystem and was mainly distributed in roots (49.5%-56.1%). Carbon density of the herbaceous layer was 22.5% of the biological carbon density of the whole ecosystem and was also mainly distributed in roots (59.6%-75.1%). The biological carbon density of P. fruticosa shrublands (5.08 t·hm^-2) was lower than the average carbon density of shrub communities in China (10. 88 t·hm^-2). Soil carbon density contributed the largest proportion (85.8%) of total carbon density in P. fruticosa shrublands.     

Atorvastatin increases human serum levels of proprotein convertase subtilisin/kexin type 9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has gained attention as a key regulator of serum low density lipoprotein cholesterol (LDL-C) levels. This novel protease causes the degradation of hepatic low density lipoprotein receptors. In humans, gain-of-function mutations in PCSK9 cause a form of familial hypercholesterolemia, whereas loss-of-function mutations result in significantly decreased LDL-C levels and cardiovascular risk. Previous studies have demonstrated that statins upregulate PCSK9 mRNA expression in cultured cells and animal models. In light of these observations, we studied the effect of atorvastatin on circulating PCSK9 protein levels in humans using a sandwich ELISA to quantitate serum PCSK9 levels in patients treated with atorvastatin or placebo for 16 weeks. We observed that atorvastatin (40 mg/day) significantly increased circulating PCSK9 levels by 34% compared with baseline and placebo and decreased LDL-C levels by 42%. These results suggest that the addition of a PCSK9 inhibitor to statin therapy may result in even further LDL-C decreases.     

Pollination success in a population of dioecious rain forest trees

Pollination success in female trees was determined for a population of Neolitsea dealbata (R. Br.) Merr., a locally abundant dioecious tree pollinated by small, unspecialized insects in northern Queensland rain forest, Australia. The population consisted of a clustered group of trees with a mean male-to-female distance of 4.5 m and more isolated individuals, including females more than 90 m away from the nearest pollen source. A map of all reproductive trees was produced to determine accurate male-to-female distances. The size of the pollen source available to females was defined as a function of the distance to the nearest ten male trees and their sizes (male neighbourhood index). The rate of pollen movement to females was measured by counting pollen tubes (and the number of tubes per style) in female trees 6 days after the commencement of population flowering. The pollination rate decreased steeply to less than half when the nearest male was only 6.5 m away. Although pollen reached a female 330 m away from the nearest pollen source, only 10% of receptive flowers had been pollinated. The short flowering period (2–3 weeks) combined with the the slow rate of pollen movement means that a large proportion of flowers in isolated trees are unpollinated, confirming an earlier finding that isolated females set fewer fruits than gregarious females. The reliability of pollen transfer to females was determined by quantifying insects and their pollen loads trapped at female trees with a range of male neighbourhood indices. Quantities of insects and pollen were significantly correlated with the size of the male neighbourhood index, indicating a strong density-dependent response by vectors to flowering. Pollen was also collected from insect visitors to non-flowering trees. Females with large male neighbourhood indices received more pollen than non-flowering trees with equivalent male neighbourhood indices. However, when the male neighbourhood indices were small for both female and non-flowering trees, the changces of pollinators encountering female and non-flowering trees were similar, suggesting random movements of pollinators in sparse-flowering sub-populations. The dioecious breeding system, brief, synchronous flowering period, clustered population structure and random, opportunistic foraging behaviour of vectors interacted in a way that reduced reproduction in relatively isolated trees. These results demonstrate a mechanism for differential breeding success between trees in natural populations and emphasize the possible impact of logging regimes on pollen flow between trees. Large interconspecific distances in species-rich environments may have been a factor in the selection for synchronous flowering between trees in outcrossing tree species with generalist insect pollinators.     

Metabolomic and physiological responses reveal multi-phasic acclimation of Arabidopsis thaliana to chronic UV radiation

Biochemical changes in vivo and pathway interactions were investigated using integrated physiological and metabolic responses of Arabidopsis thaliana L. to ultraviolet (UV) radiation (280–400 nm) at 9.96 kJ m⁻² d⁻¹ over the entire life cycle from seed to seed (8 weeks). Columbia-0 (Col-0) and a UV-B sensitive accession ( fah-1 ) showed significant ( P  < 0.001) reductions in leaf growth after 6 weeks. Col-0 recovered growth after 8 weeks, with recovery corresponding to a switch from production of phenylpropanoids to flavonoids. fah-1 failed to recover, indicating that sinapate production is an essential component of recovery. Epidermal features show that UV radiation caused significant ( P  < 0.001) increases in trichome density, which may act as a structural defence response. Stomatal indices showed a significant ( P  < 0.0001) reduction in Col-0 and a significant ( P  < 0.001) increase in fah-1 . Epidermal cell density was significantly increased under UV radiation on the abaxial leaf surface, suggesting that that a fully functioning phenylpropanoid pathway is a requirement for cell expansion and leaf development. Despite wild-type acclimation, the costs of adaptation lead to reduced plant fitness by decreasing flower numbers and total seed biomass. A multi-phasic acclimation to UV radiation and the induction of specific metabolites link stress-induced biochemical responses to enhanced acclimation.     

Competition between Brachionus calyciflorus Pallas and Brachionus patulus (Müller) (Rotifera) in relation to algal food concentration and initial population density

Competitive laboratory experiments between Brachionus calyciflorus and B. patulus were conducted at low (1×10⁶ cells ml^–1) and high (3×10⁶ cells ml^–1) densities of Chlorella vulgaris and four initial inoculation densities (numerically, 100% B. calyciflorus; 75% B. calyciflorus + 25% B. patulus; 50% each of the two species; 25% B. calyciflorus + 75% B. patulus and 100% B. patulus). Population densities were enumerated and the medium was changed daily for 20 days. B. patulus was a superior competitor in low food density regardless of inoculation density. At high food density, B. calyciflorus showed higher population growth in the first week but thereafter was outcompeted by B. patulus regardless of initial density. When grown alone, B. calyciflorus reached peak abundances (mean ± standard error) of 31±3 and 81±7 individuals ml^–1 at low and high food densities, respectively. The corresponding values for B. patulus were 130±2 and 306±13. The adverse effects of B. patulus on the peak abundances of B. calyciflorus were higher at low food concentration. Data on egg ratios (eggs female^–1) revealed an inverse relation with population abundance of both tested rotifer species. Our results indicated that the rate of population increase of a species was not a good indicator of its competitive ability. Instead, the ability to reproduce under continuously diminishing food resources (until a threshold level) was responsible for the competitive edge of B. patulus over B. calyciflorus. This was further influenced by the relative inoculation densities of the tested rotifer species and the offered food densities.     

LDL and HDL transfer rates across peripheral microvascular endothelium agree with those predicted for passive ultrafiltration in humans

The mechanisms by which LDLs and HDLs cross the vascular endothelium from plasma into interstitial fluid are not understood, and have never been studied in humans in vivo. We determined whether the plasma-to-lymph clearance rates of LDL and HDL conform with those predicted by passive ultrafiltration through intercellular pores, or if it is necessary to invoke an active process such as receptor-mediated transcytosis. Plasma and afferent peripheral lymph were collected under steady-state conditions from 30 healthy men, and assayed for seven globular proteins of molecular radii 2.89–8.95 nm, complement C3, and apo AI, apo AII, and apo B. Plasma-to-lymph clearance rates of the seven proteins fitted the relation expected for molecules of their size when transported through two populations of pores of radius 4.95 and 20.1 nm. The same model parameters were then found to accurately predict the clearance rates of both HDL and LDL. The apparent clearance of complement C3, previously shown to be secreted by cultured endothelium, exceeded that predicted by the model. We conclude that the transport of HDL and LDL from plasma into interstitial fluid across the peripheral vascular endothelium in healthy humans can be explained by ultrafiltration without invoking an additional active process such as transcytosis.     

Relations between Computational and Experimental Engineering Approaches to Molecules from Molecular Fragments

Computational techniques have become important tools in the preliminary stages of the design of new molecules. The mutual arrangements of interacting molecular parts and the required accessibility of important reactive groups on the peripheral regions of possible new molecules can be tested by computational means before the expensive and often complex synthetic methods are used to the actual construction of these molecules. There are some common features involved in the computational representation of molecular fragments and the synthetic methodologies used in the process of incorporating actual molecular fragments in such engineered molecules. One trend that appears to link these two approaches is based on the following observation: the greater local autonomy is shown by the calculated electron density contribution of a given molecular fragment, the more likely that this fragment can be regarded as a suitable building block of the molecule, and it is also more likely that there are convenient synthetic methods for the delivery of this fragment to its desired target location in the new molecule to be synthesized. For a precise formulation of this statement, a new concept, the degree of molecular fragment autonomy is introduced, using the inherent properties of molecular electron densities.     

Does trace density reflect tracemaker density? A test using intertidal gastropods on San Salvador Island,the Bahamas

Abstract

Trace densities may be a potential proxy for tracemaker densities, especially in settings where traces but not body fossils preserve well. The relationship between the density of the gastropod Batillaria minima and its trails was examined in a modern muddy intertidal zone of a lagoon on San Salvador Island, the Bahamas. The number of snails found within a quadrat was a moderately positive predictor of the number of trails that crossed the quadrat’s boundaries. This suggests in some modern ecological systems, trace density is a reasonable proxy for tracemaker density. However, in some cases, high densities of snails are found without correspondingly high trail densities, which may be driven by the snails clumping or moving little, perhaps to access shared resources. Observations of tagging individual snails and speed measurements also suggest that B. minima disperses around this type of mudflat habitat a few tens of centimeters a day.     

The apoE isoform binding properties of the VLDL receptor reveal marked differences from LRP and the LDL receptor

Apolipoprotein E (apoE) associates with lipoproteins and mediates their interaction with members of the LDL receptor family. ApoE exists as three common isoforms that have important distinct functional and biological properties. Two apoE isoforms, apoE3 and apoE4, are recognized by the LDL receptor, whereas apoE2 binds poorly to this receptor and is associated with type III hyperlipidemia. In addition, the apoE4 isoform is associated with the common late-onset familial and sporadic forms of Alzheimer's disease. Although the interaction of apoE with the LDL receptor is well characterized, the specificity of other members of this receptor family for apoE is poorly understood. In the current investigation, we have characterized the binding of apoE to the VLDL receptor and the LDL receptor-related protein (LRP). Our results indicate that like the LDL receptor, LRP prefers lipid-bound forms of apoE, but in contrast to the LDL receptor, both LRP and the VLDL receptor recognize all apoE isoforms. Interestingly, the VLDL receptor does not require the association of apoE with lipid for optimal recognition and avidly binds lipid-free apoE. It is likely that this receptor-dependent specificity for various apoE isoforms and for lipid-free versus lipid-bound forms of apoE is physiologically significant and is connected to distinct functions for these receptors.     

Influence of age and sex on levels of anti-oxidized LDL antibodies and anti-LDL immune complexes in the general population

Most studies of antibodies to oxidized LDL have been undertaken in patients with different diseases and cardiovascular risk factors. However, very few studies have researched the distribution and determining factors of antibodies to oxidized LDL in the general population. A total of 1,354 persons (817 females and 537 males) aged 5-65 years were included in this study. They were selected randomly from the population census of Málaga, in southern Spain. The females had lower levels of total cholesterol and triglycerides and higher levels of HDL-cholesterol and a very significant increase (P < 0.0001) in levels of anti-oxidized LDL [low density lipoprotein modified by malondialdehyde (MDA-LDL)] antibodies but no difference in levels of immune complexes consisting of LDL and IgG antibodies (anti-LDL immune complex). Younger persons (16-35 years) had higher levels of anti-oxidized LDL (MDA-LDL) antibodies than persons older than 35 years (P = 0.05). Levels of immune complexes were significantly higher (P = 0.05) in persons aged 5-15 years than in persons older than 40 years. A very weak association was found between levels of anti-oxidized LDL (MDA-LDL) antibodies and anti-LDL immune complexes. The higher prevalence of anti-oxidized LDL (MDA-LDL) antibodies in females and young persons is in agreement with studies that found an inverse association between atherosclerosis and the level of these antibodies.     

The evidence for Allee effects

Allee effects are an important dynamic phenomenon believed to be manifested in several population processes, notably extinction and invasion. Though widely cited in these contexts, the evidence for their strength and prevalence has not been critically evaluated. We review results from 91 studies on Allee effects in natural animal populations. We focus on empirical signatures that are used or might be used to detect Allee effects, the types of data in which Allee effects are evident, the empirical support for the occurrence of critical densities in natural populations, and differences among taxa both in the presence of Allee effects and primary causal mechanisms. We find that conclusive examples are known from Mollusca, Arthropoda, and Chordata, including three classes of vertebrates, and are most commonly documented to result from mate limitation in invertebrates and from predator–prey interactions in vertebrates. More than half of studies failed to distinguish component and demographic Allee effects in data, although the distinction is crucial to most of the population-level dynamic implications associated with Allee effects (e.g., the existence of an unstable critical density associated with strong Allee effects). Thus, although we find conclusive evidence for Allee effects due to a variety of mechanisms in natural populations of 59 animal species, we also find that existing data addressing the strength and commonness of Allee effects across species and populations is limited; evidence for a critical density for most populations is lacking. We suggest that current studies, mainly observational in nature, should be supplemented by population-scale experiments and approaches connecting component and demographic effects. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Combined effects of food level and inoculation density on competition between Brachionus patulus (Rotifera) and the cladocerans Ceriodaphnia dubia and Moina macrocopa

Competition among cladocerans and rotifers is of considerable interest not only due to their close similarity in life history strategies, but also due to the considerable overlap they exhibit in their feeding habits. In tropical waterbodies, several genera of cladocerans, including Ceriodaphnia and Moina occur, simultaneously with rotifers. We tested over a period of 3 weeks the combined effects of food (0.5×10⁶ and 1.5×10⁶ cells ml^–1 of Chlorella) level and rotifer density on the competition between B. patulus and C. dubia and M. macrocopa using population growth experiments. For each cladoceran species we used 30 test jars of 50 ml capacity. The initial density of cladocerans was 0.2 ind ml^–1, while for B. patulus it was either 1 ind ml^–1 or 5 ind ml^–1. Neither the maximal population density nor the rate of population increase (r) of C. dubia was significantly affected by B. patulus. However, for M. macrocopa, both these variables were negatively affected by the rotifers. The combined effects of low food level and high initial density of B. patulus resulted in a 50% reduction in the peak population density of M. macrocopa. The population growth of B. patulus was negatively influenced by the presence of C. dubia and M. macrocopa. The results of the competition experiments conducted in the present study between cladocerans and rotifers suggest the existence of a more complex and delicate interaction than is generally thought.     

Quantifying the Trade‐Off between Absolute Capacity and Rate Performance in Battery Electrodes

Among other things, battery electrodes need to display large absolute capacities coupled with high rate performance. However, enhancing areal capacity, for example via increased electrode thickness, results in reductions in rate performance. The basis for this negative correlation has not been studied in a quantitative fashion. Here, a semiempirical model is used to analyze capacity versus rate data for electrodes fabricated from a number of materials, each measured at various thicknesses. Fitting the model to the data outputs the low‐rate areal capacity, Q_A, and the characteristic time associated with charge/discharge, τ, fit parameters which quantify absolute capacity and rate performance respectively. A clear correlation is found between Q_A and τ, with all data siting close to a mastercurve approximately defined by constant τ/Q_A. This data is consistent with a simple model based on the timescales associated with rate‐limiting processes. This model implies that the capacity‐rate trade‐off can be improved for high areal capacity electrodes by increasing the volumetric capacity, electrical conductivity, and porosity of the electrode. Conversely, solid‐state diffusion and reaction kinetics are only important for low areal capacity electrodes.     

Effects of emulsified policosanols with different chain lengths on cholesterol metabolism in heterozygous LDL receptor-deficient mice

Policosanol is a mixture of long-chain primary aliphatic saturated alcohols. Previous studies in humans and animals have shown that these compounds improved lipoprotein profiles. However, more-recent placebo-controlled studies could not confirm these promising effects. Octacosanol (C28), the main component of sugarcane-derived policosanol, is assumed to be the bioactive component. This has, however, never been tested in an in vivo study that compared individual policosanol components side by side. Here we present that neither the individual policosanol components (C24, C26, C28, or C30) nor the natural policosanol mixture (all 30 mg/100 g diet) lowered serum cholesterol concentrations in LDL receptor knock-out (LDLr(+/-)) mice. Moreover, there was no effect on gene expression profiles of LDLr, ABCA1, HMG-CoA synthase 1, and apolipoprotein A-I (apoA-I) in hepatic and small intestinal tissue of female LDLr(+/-) mice after the 7 week intervention period. Finally, none of the individual policosanols or their respective long-chain fatty acids or aldehydes affected de novo apoA-I protein production in vitro in HepG2 and CaCo-2 cells. Therefore, we conclude that the evaluated individual policosanols, as well as the natural policosanol mixture, have no potential for reducing coronary heart disease risk through effects on serum lipoprotein concentrations.     

The glycosylation-dependent interaction of perlecan core protein with LDL: implications for atherosclerosis

Perlecan is a major heparan sulfate (HS) proteoglycan in the arterial wall. Previous studies have linked it to atherosclerosis. Perlecan contains a core protein and three HS side chains. Its core protein has five domains (DI–DV) with disparate structures and DII is highly homologous to the ligand-binding portion of LDL receptor (LDLR). The functional significance of this domain has been unknown. Here, we show that perlecan DII interacts with LDL. Importantly, the interaction largely relies on O-linked glycans that are only present in the secreted DII. Among the five repeat units of DII, most of the glycosylation sites are from the second unit, which is highly divergent and rich in serine and threonine, but has no cysteine residues. Interestingly, most of the glycans are capped by the negatively charged sialic acids, which are critical for LDL binding. We further demonstrate an additive effect of HS and DII on LDL binding. Unlike LDLR, which directs LDL uptake through endocytosis, this study uncovers a novel feature of the perlecan LDLR-like DII in receptor-mediated lipoprotein retention, which depends on its glycosylation. Thus, perlecan glycosylation may play a role in the early LDL retention during the development of atherosclerosis.     

QTL mapping for genetic determinants of lipoprotein cholesterol levels in combined crosses of inbred mouse strains

To identify additional loci that influence lipoprotein cholesterol levels, we performed quantitative trait locus (QTL) mapping in offspring of PERA/EiJxI/LnJ and PERA/EiJxDBA/2J intercrosses and in a combined data set from both crosses after 8 weeks of consumption of a high fat-diet. Most QTLs identified were concordant with homologous chromosomal regions that were associated with lipoprotein levels in human studies. We detected significant new loci for HDL cholesterol levels on chromosome (Chr) 5 (Hdlq34) and for non-HDL cholesterol levels on Chrs 15 (Nhdlq9) and 16 (Nhdlq10). In addition, the analysis of combined data sets identified a QTL for HDL cholesterol on Chr 17 that was shared between both crosses; lower HDL cholesterol levels were conferred by strain PERA. This QTL colocalized with a shared QTL for cholesterol gallstone formation detected in the same crosses. Haplotype analysis narrowed this QTL, and sequencing of the candidate genes Abcg5 and Abcg8 confirmed shared alleles in strains I/LnJ and DBA/2J that differed from the alleles in strain PERA/EiJ. In conclusion, our analysis furthers the knowledge of genetic determinants of lipoprotein cholesterol levels in inbred mice and substantiates the hypothesis that polymorphisms of Abcg5/Abcg8 contribute to individual variation in both plasma HDL cholesterol levels and susceptibility to cholesterol gallstone formation.     

Serum LDL- and HDL-cholesterol determined by ultracentrifugation and HPLC

Simple and precise methods for LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) measurements are essential for assessment of cardiovascular disease (CVD) risks and for lipid and lipoprotein studies. We report here an ultracentrifugation (UC) and HPLC method that requires substantially less specimen volume and provides the necessary reliability and throughput required by large-volume, high-quality research and clinical studies. 2-Mercaptoethanol (ME) was used to dissociate serum lipoprotein [a] (Lp[a]) into apolipoprotein [a] and Lp[a] remnant (Lp[a-]) and eliminated the contamination of Lp[a] in HDL separated by UC. Serum aliquots were centrifuged at a density of 1.006 kg/l for the separation of HDL plus LDL, and in the presence of ME at a density of 1.063 kg/l for the separation of HDL. Cholesterol concentrations of the bottom fractions were analyzed by HPLC. LDL-C and HDL-C determined using this method were equivalent to those with β-quantification and the designated comparison method of the Centers for Disease Control. The total coefficient of variations for LDL-C and HDL-C were 0.65-1.12% and 0.96-2.07%, respectively. This method requires a small amount of specimen and is easy to operate. This method may be used in research or in clinical laboratories where precise and specific lipoprotein cholesterol analysis is needed.     

The fatty acid distribution in low density lipoprotein in diabetes

Atherosclerosis is commonly found in diabetes. There is an association between small dense low density lipoprotein (LDL) phenotype, which is more prevalent in the diabetic state, and atherosclerosis. Small dense LDL is more easily oxidised and it is possible that fatty acid compositional changes, particularly an increase in polyunsaturated fatty acids, could underlie this association. However, there is little information about fatty acids in the different LDL phenotypes in the literature. This study examined LDL subfraction composition in 18 non-insulin-dependent diabetic (NIDDM) patients and 11 control subjects. LDL was isolated and fractionated into LDL 1, 2 and 3 by density gradient ultracentrifugation. NIDDM patients had significantly more fatty acids in all LDL subfractions than control subjects (P<0.01). Palmitic and linoleic acid were significantly greater in all subfractions in the diabetic patients compared to control subjects (P<0.01) and palmitoleic and oleic acids were also greater in LDL1 and LDL2 in diabetic patients (P<0.01). We conclude that in NIDDM fatty acids are increased in all LDL subfractions and this may be the reason for the increased atherosclerosis in diabetes irrespective of phenotype.