Hyphal growth and mycorrhiza formation by the arbuscular mycorrhizal fungus Glomus claroideum BEG 23 is stimulated by humic substances

Effects of humic substances (humic acid or fulvic soil extract) or saprophytic microorganisms (Paecilomyces lilacinus and an unidentified actinomycete) on growth of mycelium and mycorrhiza formation by Glomus claroideum BEG23 were studied in a hydroponic system. Humic substances stimulated root colonization and production of extraradical mycelium by the mycorrhizal fungus. Both humic and fulvic acids tended to decrease populations of culturable bacteria and fungi in the cultivation system, indicating a moderately antibiotic activity. The addition of saprophytic microorganisms able to use humic substances to the cultivation system further stimulated the development of the mycorrhizal fungus. However, stimulation of G. claroideum was also observed when the saprophytic microorganisms were heat-killed, suggesting that their effect was not linked to a specific action on humic substances. The results indicate that humic substances may represent a stimulatory component of the soil environment with respect to arbuscular mycorrhizal fungi.     

Changes of enzyme activity in lipid signaling pathways related to substrate reordering

The static fluid mosaic model of biological membranes has been progressively complemented by a dynamic membrane model that includes phospholipid reordering in domains that are proposed to extend from nanometers to microns. Kinetic models for lipolytic enzymes have only been developed for homogeneous lipid phases. In this work, we develop a generalization of the well-known surface dilution kinetic theory to cases where, in a same lipid phase, both domain and nondomain phases coexist. Our model also allows understanding the changes in enzymatic activity due to a decrease of free substrate concentration when domains are induced by peptides. This lipid reordering and domain dynamics can affect the activity of lipolytic enzymes, and can provide a simple explanation for how basic peptides, with a strong direct interaction with acidic phospholipids (such as beta-amyloid peptide), may cause a complex modulation of the activities of many important enzymes in lipid signaling pathways.     

Miscibility of acyl-chain defined phosphatidylcholines with N-palmitoyl sphingomyelin in bilayer membranes

In this study we have used differential scanning calorimetry (DSC) to study the miscibility of different saturated phosphatidylcholines (PCs) with d-erythro-N-palmitoyl-sphingomyelin (16:0-SM). Information about the miscibility was obtained by observing the thermotropic phase behavior of binary mixtures of saturated PCs and 16:0-SM. The results obtained showed that PC miscibility in 16:0-SM was markedly affected by the PC acyl-chain composition. According to phase diagrams prepared from DSC data and the mid-transition temperatures of the main phase transition, the PC which formed the most ideal mixture with 16:0-SM was di-14:0-PC. However, the cooperativity of the main transition in PC/16:0-SM bilayers increased until the average acyl-chain length in the PC reached 15 carbons. Based on the criteria of the most ideal miscibility or the highest cooperativity of the main transition, we conclude that di-14:0-PC, 15:0/15:0-PC, and 14:0/16:0-PC interacted most favorably with 16:0-SM in bilayer membranes. Di-16:0-PC, to which 16:0-SM is often compared in biophysical studies, showed much less ideal miscibility.     

Biomass allocation in herbaceous plants under grazing impact in the high semi-arid Andes

Among the plant traits that affect performance, vitality and herbivore resistance in rangeland vegetation, biomass partitioning ranks top, commonly outweighing processes at single leaves (e.g., photosynthesis, respiration). We explored the allometry of a broad sample of herbaceous species from two high elevation sites in the Andes in order to explain biomass partitioning under harsh climatic conditions and risk of biomass losses under strong camelid grazing pressure. We combined data from NW-Argentina and W-Bolivia from elevations between 4200 and 4250 m in a landscape dominated by tall Festuca orthophylla tussocks and a drought driven seasonality (rainfall only between November and March). Across 10–20 taxa per region we found less investment in leaves with a mean leaf mass fraction of only 11% and instead a massive storage in below-ground compartments (rhizomes, tap roots), particularly at the colder Argentinean site. Though grazing pressure was much greater in Bolivia, the foliage mass fraction was there larger than in Argentina. The inter-tussock space in these open, dry plains (‘pajonal’) was dominated by rosette forming species with a below-ground shoot apex and massive tap roots (70% of all species), rendering these species less sensitive to grazing and trampling. The storage organs of these species represented more than 50% of total biomass. Llamas, which represented the main vertebrate herbivore in these open plains at the Bolivian site, preferred non tap-root herbs and species with low leaf nitrogen concentration. Palatable forbs for llamas (22% of all species at the Bolivian site) only survived when nested (facilitated) in the rigid, tall Festuca orthophylla tussocks or thorny shrubs. In conclusion, these extremely high elevation rangeland herbs invest preferentially in structures for persistence (K-strategy) rather than maximizing carbon gain.     

Characterization of cryobiological responses in TF-1 cells using interrupted freezing procedures

Cryopreservation currently is the only method for long-term preservation of cellular viability and function for uses in cellular therapies. Characterizing the cryobiological response of a cell type is essential in the approach to designing and optimizing cryopreservation protocols. For cells used in therapies, there is significant interest in designing cryopreservation protocols that do not rely on dimethyl sulfoxide (Me₂SO) as a cryoprotectant, since this cryoprotectant has been shown to have adverse effects on hematopoietic stem cell (HSC) transplant patients. This study characterized the cryobiological responses of the human erythroleukemic stem cell line TF-1, as a model for HSC. We measured the osmotic parameters of TF-1 cells, including the osmotically-inactive fraction, temperature-dependent membrane hydraulic conductivity and the membrane permeability to 1 M Me₂SO. A two-step freezing procedure (interrupted rapid cooling with hold time) and a graded freezing procedure (interrupted slow cooling without hold time) were used to characterize TF-1 cell recovery during various phases of the cooling process. One outcome of these experiments was high recovery of TF-1 cells cryopreserved in the absence of traditional cryoprotectants. The results of this study of the cryobiology of TF-1 cells will be critical for future understanding of the cryobiology of HSC, and to the design of cryopreservation protocols with specific design criteria for applications in cellular therapies.     

Light-dependent subcellular localization of nucleoside diphosphate kinase-1 in Neurospora crassa

Nucleoside diphosphate kinase (NDK) is a housekeeping enzyme localized in cellular organelles and distributed in various organs in prokaryotes and eukaryotes. In Neurospora crassa, NDK-1 is suggested to control catalases in response to heat, oxidative stress and light. In this study, we identified the presence of NDK-1 during most developmental stages in submerged mycelia, aerial hyphae, asexual conidia and perithecia, and the localization of it in soluble, mitochondrial, nuclear and membrane fractions in the mycelial cell. A light-dependent localization of NDK-1 was shown by Western blotting and immunohistochemical analysis using anti-NDK-1 antibody. In the mycelia, NDK-1 was compartmentalized on the plasma membrane in darkness, while it was relocated in the cytoplasm under light. These results suggest that NDK-1 protein was translocated from the plasma membrane to cytoplasm in response to light, and may interact with catalase.     

Biochemical Origin and Refractory Properties of Humic Acid Extracted from the Maize Plant

Humic acids (HA) contribute to soil fertility because of their chemical, physical, and biological properties. The origin of HAs in soils has puzzled scientists for decades, and what HAs are and what their origin is remain unclear. The isolation of HAs in plants, which have characteristics close to soil HAs, suggests the probable origin of soil-HA is the preservation of plant tissue, indicating biochemical origin. In this paper HA from maize plant at different stages of maturity is isolated, from which it was found that the evolution of this fraction depends on and is derived from cell wall formation. Evidence was also found that HA was above all composed of lignin and cutin residues, and was characterized by low surface area. After 8 months of incubation in both mineral-artificial and natural soils, humic acid isolated form maize plant could be recovered intact.     

A cell-free biochemical complementation assay reveals complex and redundant cytosolic requirements for LRP endocytosis

The low density lipoprotein receptor-related protein (LRP) binds multiple, distinct ligands and participates in constitutive endocytosis and signal transduction. Using an in vitro reconstitution system and a new biochemical complementation assay, we have explored the limiting cytosolic requirements for endocytosis of LRP from isolated plasma membranes. We find that clathrin, AP2 and dynamin do not support efficient LRP uptake and that additional factors present in a 30% ammonium sulfate supernatant fraction of bovine brain cytosol (AS supt) are required. Fractionation of the AS supt revealed that multiple and redundant factors are required to support LRP endocytosis. Among these, we identified Hsc70, synaptojanin1 and CRMP-2 by mass spectrometry. Our data suggest that LRP, which bears several distinct endocytic motifs in its cytoplasmic domain, may use multiple pathways for endocytosis in vitro.     

Heat shock protein 60 modified with O-linked N-acetylglucosamine is involved in pancreatic beta-cell death under hyperglycemic conditions

The objective of this study was to identify proteins modified with O-linked N-acetylglucosamine (O-GlcNAc) in pancreatic beta-cells and to understand their roles in cell death under hyperglycemic conditions. Here we report that heat shock protein 60 (HSP60) is modified with O-GlcNAc. Levels of O-GlcNAcylated HSP60 increased twofold in response to hyperglycemic conditions. HSP60 is a chaperonin known to bind to Bax in the cytoplasm under normoglycemic conditions. Under hyperglycemic conditions, Bax detached from O-GlcNAcylated HSP60 and translocated to mitochondria. Hyperglycemic conditions were also associated with cytochrome c release, caspase-3 activation, and cell death, suggesting that elevated O-GlcNAcylation of HSP60 interferes with HSP60-Bax interactions, leading to pancreatic beta-cell death.     

Attributable risk function in the proportional hazards model for censored time-to-event

Time-to-event endpoints are often used in clinical and epidemiological studies to evaluate disease association with hazardous exposures. In the statistical literature of time-to-event analysis, such association is usually measured by the hazard ratio in the proportional hazards model. In public health, it is also of important interest to assess the excess risk attributable to an exposure in a given population. In this article, we extend the notion of 'population attributable fraction' for the binary outcomes to the attributable risk function for the event times in prospective studies. A simple estimator of the time-varying attributable risk function is proposed under the proportional hazards model. Its inference procedures are established. Monte-Carlo simulation studies are conducted to evaluate its validity and performance. The proposed methodology is motivated and demonstrated by the data collected in a multicenter acquired immunodeficiency syndrome (AIDS) cohort study to estimate the attributable risk of human immunodeficiency virus type 1 (HIV-1) infections due to several potential risk factors.