Senescence rates are determined by ranking on the fast-slow life-history continuum

Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history – survival or recruitment – can provide reliable information on overall senescence.     

Litter decomposition rates in Canadian forests

The effect of litter quality and climate on the rate of decomposition of plant tissues was examined by the measurement of mass remaining after 3 years’ exposure of 11 litter types placed at 18 forest sites across Canada. Amongst sites, mass remaining was strongly related to mean annual temperature and precipitation and amongst litter types the ratio of Klason lignin to nitrogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean annual precipitation and Klason lignin:nitrogen ratio explained 73% of the variance in mass remaining for all sites and tissues. Using three doubled CO₂ GCM climate change scenarios for four Canadian regions, these relationships were used to predict increases in decomposition rate of 4–7% of contemporary rates (based on mass remaining after 3 years), because of increased temperature and precipitation. This increase may be partially offset by evidence that plants growing under elevated atmospheric CO₂ concentrations produce litter with high lignin:nitrogen ratios which slows the rate of decomposition, but this change will be small compared to the increased rate of decomposition derived from climatic changes.     

Induction and decay of thermotolerance in human erythrocytes determined by hemolysis

Hemolysis was used as an endpoint for the measurement of damage to the plasma membrane in human erythrocytes after a single or a double heat shock. The thermotolerance of erythrocytes is a transitional phenomenon, reaching its maximum at a 3-hour incubation at 37 degrees C between the heat shocks.     

Litter decay controlled by temperature,not soil properties,affecting future soil carbon

Widespread global changes, including rising atmospheric CO₂ concentrations, climate warming and loss of biodiversity, are predicted for this century; all of these will affect terrestrial ecosystem processes like plant litter decomposition. Conversely, increased plant litter decomposition can have potential carbon‐cycle feedbacks on atmospheric CO₂ levels, climate warming and biodiversity. But predicting litter decomposition is difficult because of many interacting factors related to the chemical, physical and biological properties of soil, as well as to climate and agricultural management practices. We applied ¹³C‐labelled plant litter to soil at ten sites spanning a 3500‐km transect across the agricultural regions of Canada and measured its decomposition over five years. Despite large differences in soil type and climatic conditions, we found that the kinetics of litter decomposition were similar once the effect of temperature had been removed, indicating no measurable effect of soil properties. A two‐pool exponential decay model expressing undecomposed carbon simply as a function of thermal time accurately described kinetics of decomposition. (R² = 0.94; RMSE = 0.0508). Soil properties such as texture, cation exchange capacity, pH and moisture, although very different among sites, had minimal discernible influence on decomposition kinetics. Using this kinetic model under different climate change scenarios, we projected that the time required to decompose 50% of the litter (i.e. the labile fractions) would be reduced by 1–4 months, whereas time required to decompose 90% of the litter (including recalcitrant fractions) would be reduced by 1 year in cooler sites to as much as 2 years in warmer sites. These findings confirm quantitatively the sensitivity of litter decomposition to temperature increases and demonstrate how climate change may constrain future soil carbon storage, an effect apparently not influenced by soil properties.     

Order and fluidity of lipid membranes as determined by fluorescence anisotropy decay

The fluorescence anisotropy decay of four different probes in bilayers of dimyristoylphosphatidylcholine was measured. The probes are diphenylhexatriene, diphenyloctatetraene, trimethylaminodiphenylhexatriene, and trans-parinaric acid. The data for each probe were analyzed in terms of two orientational order parameters, the ordinary order parameter and a higher one, and two rotational diffusion coefficients. The order parameters are largely independent of probe size, but depend on the position of the probes along the membrane normal, thus reflecting the profile of lipid order. If a probe is located in the plateau region of lipid order, its order parameters are interpreted as representing the rigid-body order of lipids. According to this interpretation, the total lipid order in the plateau region originates about equally from rigid-body order and conformational order. The two order parameters obtained for each probe are used to derive approximate angular distributions of the probe molecules. The diffusion coefficient for rotation about the long molecular axis is found to be infinitely large, indicating unhindered rotation about this axis. The diffusion coefficient for rotation about the short molecular axes is evaluated for a viscosity which results as 0.2 poise. This viscosity for rotational diffusion is an order of magnitude smaller than the viscosity for lateral diffusion indicating that at least two viscosities are required to characterize the fluidity of a lipid membrane.Abbreviations FAD fluorescence anisotropy decay - DMR deuterium magnetic resonance - ESR electron spin resonance - DMPC dimyristoylphosphatidylcholine - DPPC dipalmitoylphosphatidylcholine - DPH 1,6-diphenyl-1,3,5-hexatriene - DPO 1,6-diphenyl-1,3,5,7-octatetraene - TMA-DPH 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene - tPnA trans-parinaric acid - NPN N-phenyl-1-naphthylamine - BBO 2,5-bis(4-biphenylyl)oxazole     

Photorespiratory rates in wheat and maize as determined by o-labeling

A method was devised to quantify short-term photorespiratory rates in terrestrial plants using ¹⁸O-intermediates of the glycolate pathway, specifically glycolate, glycine, and serine. The pathway intermediates were isolated and analyzed on a GC/MS to determine molecular percent ¹⁸O-enrichment. Rates of glycolate synthesis were determined from ¹⁸O-labeling kinetics of the intermediates, derived rate equations, and nonlinear regression techniques. Glycolate synthesis in wheat (Triticum aestivum L.), a C₃ plant, and maize (Zea mays L.), a C₄ plant, was stimulated by high O₂ concentrations and inhibited by high CO₂ concentrations. The synthesis rates were 7.3, 2.1, and 0.7 micromoles per square decimeter per minute under a 21% O₂ and 0.035% CO₂ atmosphere for leaf tissue of wheat, maize seedlings, and 3-month-old maize, respectively. Photorespiratory CO₂ evolution rates were estimated to be 27, 6, and 2%, respectively, of net photosynthesis for the three groups of plants under the above atmosphere. The results from maize tissue support the hypothesis that C₄ plants photorespire, albeit at a reduced rate in comparison to C₃ plants, and that the CO₂/O₂ ratio in the bundle sheath of maize is higher in mature tissue than in seedling tissue. The pool size of the three photorespiratory intermediates remained constant and were unaffected by changes in either CO₂ or O₂ concentrations throughout the 10-minute labeling period. This suggests that photorespiratory metabolism is regulated by other mechanism besides phosphoglycolate synthesis by ribulose-1,5-bisphosphate carboxylase/oxygenase, at least under short-term conditions. Other mechanisms could be alternate modes of synthesis of the intermediates, regulation of some of the enzymes of the photorespiratory pathway, or regulation of carbon flow between organelles involved in photorespiration. The glycolate pool became nearly 100% ¹⁸O-labeled under an atmosphere of 40% O₂. This pool failed to become 100% ¹⁸O-enriched under lower O₂ concentrations.     

Unfolding rates of globular proteins determined by kinetics of proteolysis

A convenient method for the determination of unfolding rates of small globular proteins under physiological conditions was developed using digestion with proteases. The apparent first-order rate constants for digestion of lysozyme with thermolysin and with Pronase at pH 8 and 50 degrees C were shown to be saturated with increases of concentrations of these proteases. The maximum rate constants extrapolated were identical in digestions with two different proteases, and were found to be equal to the unfolding rate constant of lysozyme. Similarly, the unfolding rate constant of RNase A at pH 8 and 50 degrees C, and those of lysozyme, RNase A and beta-lactoglobulin at pH 8 and 40 degrees C, were determined by the digestion method. Thus, it was shown that digestion by proteases proceeds mainly via the unfolded state of proteins.     

Inadequate rates are lower when FNAC samples are taken by cytopathologists

Inadequate rates (IR) in FNAC from different sources were compared. The rates were lowest when FNAC was performed by a cytopathologist (12%) and highest when done by a non-cytopathologist (32%). These differences were mirrored in high IRs in breast cancer cases. IR was not significantly improved when non-cytopathologist FNAC was attended by a cytotechnician.     

Lignocellulosic polysaccharides and lignin degradation by wood decay fungi: the relevance of nonenzymatic Fenton-based reactions

The brown rot fungus Wolfiporia cocos and the selective white rot fungus Perenniporia medulla-panis produce peptides and phenolate-derivative compounds as low molecular weight Fe³⁺-reductants. Phenolates were the major compounds with Fe³⁺-reducing activity in both fungi and displayed Fe³⁺-reducing activity at pH 2.0 and 4.5 in the absence and presence of oxalic acid. The chemical structures of these compounds were identified. Together with Fe³⁺ and H₂O₂ (mediated Fenton reaction) they produced oxygen radicals that oxidized lignocellulosic polysaccharides and lignin extensively in vitro under conditions similar to those found in vivo. These results indicate that, in addition to the extensively studied Gloeophyllum trabeum—a model brown rot fungus—other brown rot fungi as well as selective white rot fungi, possess the means to promote Fenton chemistry to degrade cellulose and hemicellulose, and to modify lignin. Moreover, new information is provided, particularly regarding how lignin is attacked, and either repolymerized or solubilized depending on the type of fungal attack, and suggests a new pathway for selective white rot degradation of wood. The importance of Fenton reactions mediated by phenolates operating separately or synergistically with carbohydrate-degrading enzymes in brown rot fungi, and lignin-modifying enzymes in white rot fungi is discussed. This research improves our understanding of natural processes in carbon cycling in the environment, which may enable the exploration of novel methods for bioconversion of lignocellulose in the production of biofuels or polymers, in addition to the development of new and better ways to protect wood from degradation by microorganisms.     

Differential antigen decay rates during digestion of molluscan prey by carabid predators

Carabid beetles (Coleoptera: Carabidae) were fed upon slugs (Mollusca: Pulmonata) in the laboratory, and their crop contents analysed for mollusc remains, using an enzyme-linked immunosorbent assay (ELISA) with an anti-Arion ater (L.) haemolymph antiserum. Crop weight loss and antigenic recognition of prey proteins were examined as separate variables in a series of validatory experiments. Two model predators,Abax parallelepipedus Piller and Mitterpacher andPterostichus madidus F., were fed upon two species of pest slugs,Deroceras reticulatum (Müller) andArion hortensis Férussac. The fitting of regression equations to the transformed antigenic response data allowed the ‘half-life’ and detection period to be calculated for each predator-prey combination. Following a one hour feeding interval, the half-life of the antigenic response toD. reticulatum remains was almost twice as long inP. madidus as that inA. parallelepipedus, and the detection period more than 2.5 times as long. However, covariant analysis showed that there was a significant difference between predator species in the rate at which detectability declined, but not in the rate of crop weight loss. WhenA. parallelepipedus was allowed to feed uponA. hortensis for eight hours, prey remains were still detectable at the end of the experiment, 13 days after feeding. Calibration of the differential rates of antigen decay and crop weight loss could potentially be used to calculate the size of the original meal, but only if prey species, and the time since feeding, can be determined. Potential solutions to these problems are discussed.     

Dynamics of melittin in water and membranes as determined by fluorescence anisotropy decay.

Fluorescence anisotropy decay measurements were performed on melittin in water and in membranes of dimyristoylphosphatidylcholine. The fluorescence of the single tryptophan residue of melittin and of a pyrene label attached to melittin was detected. In water, the slowest relaxation process in the anisotropy decay occurs with a relaxation time of 1.5 or 5.5 ns in the case of low or high ionic strength and corresponds to rotational diffusion of monomeric or tetrameric melittin. Superimposed on this slow process are fast processes in the subnanosecond range reflecting fluctuations of the fluorophores relative to the polypeptide backbone. In membranes, the fast relaxation processes are not much altered. A slow process with a relaxation time of 35 ns is observed and assigned to orientational fluctuations of the melittin helices in membranes.     

Outcomes of fungal interactions are determined by soil invertebrate grazers

Saprotrophic fungal community composition, determined by the outcome of competitive mycelial interactions, is one of the many key factors affecting soil nutrient mineralisation and decomposition rates. Fungal communities are not generally predicted to be regulated by top-down factors, such as predation, but rather by bottom-up factors, including resource availability. We show that invertebrate grazers can exert selective pressures on fungal decomposer communities in soil, reversing the outcomes of competitive interactions. By feeding selectively on the cord-forming fungus Resinicium bicolor, isopods prevented the competitive exclusion of Hypholoma fasciculare and Phanerochaete velutina in soil and wood. Nematode populations also reversed the outcomes of competitive interactions by stimulating growth of less competitive fungi. These represent two opposing mechanisms by which soil fauna may influence fungal community composition and diversity. Factors affecting soil invertebrate communities will have direct consequences for fungal-mediated nutrient cycling in woodland soils.     

Peroxyl radicals are potential agents of lignin biodegradation

Past work has shown that the extracellular manganese-dependent peroxidases (MnPs) of ligninolytic fungi degrade the principal non-phenolic structures of lignin when they peroxidize unsaturated fatty acids. This reaction is likely to be relevant to ligninolysis in sound wood, where enzymes cannot penetrate, only if it employs a small, diffusible lipid radical as the proximal oxidant of lignin. Here we show that a non-phenolic beta-O-4-linked lignin model dimer was oxidized to products indicative of hydrogen abstraction and electron transfer by three different peroxyl radical-generating systems: (a) MnP/Mn(II)/linoleic acid, (b) arachidonic acid in which peroxidation was initiated by a small amount of H(2)O(2)/Fe(II), and (c) the thermolysis in air of either 4,4'-azobis(4-cyanovaleric acid) or 2,2'-azobis(2-methylpropionamidine) dihydrochloride. Some quantitative differences in the product distributions were found, but these were attributable to the presence of electron-withdrawing substituents on the peroxyl radicals derived from azo precursors. Our results introduce a new hypothesis: that biogenic peroxyl radicals may be agents of lignin biodegradation.     

Grazing rates of the freshwater ciliate Balanion planctonicum determined by flow cytometry

Feeding of Balanion planctonicum on the cryptomonad Rhodomonassp. was recorded in vivo at 2–3 min intervals by flowcytometry. Ingestion rates were 1.6–1.7 algal cells ciliate^–1h^–1. On average, 20–30 min elapsed between ingestionand egestion.     

Litter fall and litter layer decay in coastal scrub at Sydney,Australia

Summary Seasonal litter fall and changes in dry weight and minerals within the litter layer were sampled throughout one year. The annual total litter fall was 4.9 t per hectare of which 70% was leaf fall. Litter fall was highest in spring and early summer, the falls of each component (leaf, wood, etc.) and species being markedly seasonal but not all in phase. The annual amounts of minerals cycling as litter fall ranged from 44 kg N to 2 kg P per hectare. Mineral concentrations of the litter fall underwent seasonal variation and in the case of potassium were related to rainfall. The litter layer, mean biomass 19 t ha^-1, declined in weight at a rate of 2.4% per week between spring and summer. The mean turnover time for the dry weight of the litter layer was 3.8 years and for the mineral approx. 1 year (K, Cl) or in excess of 3 years (P, Ca, S, Mg and N).     

G-quadruplex conformation and dynamics are determined by loop length and sequence

The quadruplex forming G-rich sequences are unevenly distributed throughout the human genome. Their enrichment in oncogenic promoters and telomeres has generated interest in targeting G-quadruplex (GQ) for an anticancer therapy. Here, we present a quantitative analysis on the conformations and dynamics of GQ forming sequences measured by single molecule fluorescence. Additionally, we relate these properties to GQ targeting ligands and G4 resolvase 1 (G4R1) protein binding. Our result shows that both the loop (non-G components) length and sequence contribute to the conformation of the GQ. Real time single molecule traces reveal that the folding dynamics also depend on the loop composition. We demonstrate that GQ-stabilizing small molecules, N-methyl mesoporphyrin IX (NMM), its analog, NMP and the G4R1 protein bind selectively to the parallel GQ conformation. Our findings point to the complexity of GQ folding governed by the loop length and sequence and how the GQ conformation determines the small molecule and protein binding propensity.     

HCMV spread and cell tropism are determined by distinct virus populations

Human cytomegalovirus (HCMV) can infect many different cell types in vivo. Two gH/gL complexes are used for entry into cells. gH/gL/pUL(128,130,131A) shows no selectivity for its host cell, whereas formation of a gH/gL/gO complex only restricts the tropism mainly to fibroblasts. Here, we describe that depending on the cell type in which virus replication takes place, virus carrying the gH/gL/pUL(128,130,131A) complex is either released or retained cell-associated. We observed that virus spread in fibroblast cultures was predominantly supernatant-driven, whereas spread in endothelial cell (EC) cultures was predominantly focal. This was due to properties of virus released from fibroblasts and EC. Fibroblasts released virus which could infect both fibroblasts and EC. In contrast, EC released virus which readily infected fibroblasts, but was barely able to infect EC. The EC infection capacities of virus released from fibroblasts or EC correlated with respectively high or low amounts of gH/gL/pUL(128,130,131A) in virus particles. Moreover, we found that focal spread in EC cultures could be attributed to EC-tropic virus tightly associated with EC and not released into the supernatant. Preincubation of fibroblast-derived virus progeny with EC or beads coated with pUL131A-specific antibodies depleted the fraction that could infect EC, and left a fraction that could predominantly infect fibroblasts. These data strongly suggest that HCMV progeny is composed of distinct virus populations. EC specifically retain the EC-tropic population, whereas fibroblasts release EC-tropic and non EC-tropic virus. Our findings offer completely new views on how HCMV spread may be controlled by its host cells.