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At least 433 records · Page 24Linked to original sources
PubMed2024

Brood indicators are an early warning signal of honey bee colony loss-a simulation-based study.

Honey bees (Apis mellifera) are exposed to multiple stressors such as pesticides, lack of forage, and diseases. It is therefore a long-standing aim to develop robust and meaningful indicators of bee vitality to assist beekeepers While established indicators often focus on expected colony winter mortality based on adult bee abundance and honey reserves at the beginning of the winter, it would be useful to have indicators that allow detection of stress effects earlier in the year to allow for adaptive management. We used the established honey bee simulation model BEEHAVE to explore the potential of different indicators such as population size, number of capped brood cells, flight activity, abundance of Varroa mites, honey stores and a brood-bee ratio. We implemented two types of stressors in our simulations: 1) parasite pressure, i.e. sub-optimal Varroa treatment by the beekeeper (hereafter referred as Biotic stress) and 2) temporal forage gaps in spring and autumn (hereafter referred as Environmental stress). Neither stressor type could be detected by bee abundance or honey reserves at the end of the first year. However, all response variables used in this study did reveal early warning signals during the course of the year. The most reliable and useful measures seem to be related to brood and the abundance of Varroa mites at the end of the year. However, while in the model we have full access to time series of variables from stressed and unstressed colonies, knowledge of these variables in the field is challenging. We discuss how our findings can nevertheless be used to develop practical early warning indicators. As a next step in the interactive development of such indicators we suggest empirical studies on the importance of the number of capped brood cells at certain times of the year on bee population vitality.

Bees↗
PubMed2002

Immune response to parasitic attack: evolution of a pulsed character.

Pulsed characters are temporary biochemical, cellular, or structural changes produced in response to environmental or biotic challenge. For example, response to parasitic attack develops as a pulse of defensive chemicals or cells that typically decay after the parasite has been controlled. Almost all theories for the genetic variability of characters assume measurements on static characters. This paper presents theoretical tools to examine optimal control variables for pulsed characters and the expected level of genetic variability in those control variables. The example of host immune response to parasitic attack is used to develop the theory.

Biological Evolution↗
PubMed1998

Differential expression of a senescence-enhanced metallothionein gene in Arabidopsis in response to isolates of Peronospora parasitica and Pseudomonas syringae.

The metallothionein gene, LSC54, shows increased expression during leaf senescence in Brassica napus and Arabidopsis thaliana. A number of abiotic and biotic stresses have been shown to induce senescence-like symptoms in plants and, to investigate this further, the promoter of the LSC54 gene was cloned and fused to the GUS gene and transformed into Arabidopsis. The promoter was highly induced during leaf senescence and also in response to wounding; histochemical analysis indicated that this induction was localised to a few cells close to the wound site. The transgenic Arabidopsis tissue was infected with compatible and incompatible isolates of both the fungal biotroph, Peronospora parasitica and the bacterial necrotroph, Pseudomonas syringae. Incompatible isolates induced rapid cell death (the hypersensitive response) at the site of infection and, with both pathogens, early, localised expression of the GUS gene was observed. In contrast, relatively slow induction of the GUS gene was seen in the compatible interaction and this was correlated with the appearance of senescence-like symptoms in the biotrophic interaction and cell death by necrosis that occurred in response to the necrotrophic pathogen. These results suggest that there are common steps in the signalling pathways that lead to cell death in the hypersensitive response, pathogen induced necrosis and senescence.

Arabidopsis↗
PubMed1999

The evolution of mass balance models of persistent organic pollutant fate in the environment.

Current approaches to modelling the fate of persistent organic pollutants (POPs) in the environment have evolved in response to four dominant characteristics of these substances; namely: (1) the presence of POPs in virtually all environmental phases and the ease with which they move from one to the other requires multi-compartmental modelling. Describing transport across phase boundaries becomes as, or even more, important as quantifying transport within the phases; (2) POPs may persist in the environment for many decades. For chemicals that 'have time', concepts such as equilibrium partitioning and steady-state become more important than for short-lived substances whose fate is more controlled by the rates of transformation; (3) measuring POPs is difficult and expensive and observed concentrations of POPs are not available in high spatial or temporal resolution. Consequently, high resolution tends not to be a high priority in POP models; and (4) detrimental effects of POPs often manifest themselves in top predators, which has led to a focus on modelling biotic uptake and transfer within food chains. The task of building a POPs model is viewed as combining the four 'building blocks' of partitioning, transport, transformation and source data with the help of the law of the conservation of mass. Process models, evaluative models, models of real local, regional and global fate, as well as biological uptake models are presented and references to numerous examples are provided. An attempt is made to forecast future directions in the field of POPs modelling. It is expected that modelling techniques that do not rely on quantitative emission estimates as well as approaches that take into account spatial, temporal and climatic variability as well as parameter uncertainty will increase in importance. Finally, the relationship between modelling POPs and models of other pollutant issues is addressed, as are potential interactions between POPs and pollutant issues such as eutrophication, acidification and global climate change.

Journal Article↗
PubMed1999

Interaction between specific hydrological and microbial activity leading to extensive mucilage formation in the northern Adriatic Sea.

The massive formation of marine snow and the senescent stage of it, the mucilage, is a phenomenon largely restricted to the Adriatic Sea. In this contribution the major environmental factors potentially leading to the formation of this mucilage are discussed. It is proposed that the specific hydrological conditions in combination with severe phosphorus depletion lead to excessive formation of colloidal organic matter by phytoplankton. This colloidal organic matter coagulates to marine snow due to the low-turbulence regimes prevailing in the water column. Subsequently, this marine snow is colonized by bacteria which, in turn, produce and release copious amounts of capsular polymers into the matrix of marine snow. It is speculated that a significant fraction of the later stages of marine snow (mucilage) consists of bacterial-derived organic matter which has been shown to be semi-labile to refractory for further bacterial utilization. The marine snow matrix acts as efficient adsorption site and allows the bacteria to utilize scavenged molecules from the ambient water. Thus it is proposed that the matrix ages without significant biotic degradation.

Colloids↗
PubMed2003

Chromium-microorganism interactions in soils: remediation implications.

Discharge of Cr waste from many industrial applications such as leather tanning, textile production, electroplating, metallurgy, and petroleum refinery has led to large-scale contamination of land and water. Generally, Cr exists in two stable states: Cr(III) and Cr(VI). Cr(III) is not very soluble and is immobilized by precipitation as hydroxides. Cr(VI) is toxic, soluble, and easily transported to water resources. Cr(VI) undergoes rapid reduction to Cr(III), in the presence of organic sources or other reducing compounds as electron donors, to become precipitated as hydroxides. Cr(VI)-reducing microorganisms are ubiquitous in soil and water. A wide range of microorganisms, including bacteria, yeasts; and algae, with exceptional ability to reduce Cr(VI) to Cr(III) anaerobically and/or aerobically, have been isolated from Cr-contaminated and noncontaminated soils and water. Bioremediation approaches using the Cr(VI)-reducing ability of introduced (in bioreactors) or indigenous (augmented by supplements with organic amendments) microorganisms has been more successful for remediation of Cr-contaminated water than soils. Apart from enzymatic reduction, nonenzymatic reduction of Cr(VI) can also be common and widespread in the environment. For instance, biotic-abiotic coupling reactions involving the microbially formed products, H2S (the end product of sulfate reduction), Fe(II) [formed by Fe(III) reduction], and sulfite (formed during oxidation of elemental sulfur), can mediate the dissimilatory reduction of Cr(VI). Despite the dominant occurrence of enzymatic and nonenzymatic reduction of Cr(VI), natural attenuation of Cr(VI) is not taking place at a long-term contaminated site in South Australia, even 225 years after the last disposal of tannery waste. Evidence suggests that excess moisture conditions leading to saturation or flooded conditions promote the complete removal of Cr(VI) in soil samples from this contaminated site; but Cr(VI) reappears, probably because of oxidation of the Cr(III) by Mn oxides, with a subsequent shift to drying conditions in the soil. In such environments with low natural attenuation capacity resulting from reversible oxidation of Cr(III), bioeremediation of Cr(VI) can be a challenging task.

Bacteria, Anaerobic↗
PubMed2000

In vivo regulation of protein synthesis by phosphorylation of the alpha subunit of wheat eukaryotic initiation factor 2.

The regulation of protein synthesis is a critical component in the maintenance of cellular homeostasis. A major mechanism of translational control in response to diverse abiotic and biotic stress signals involves the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha). The pathway has been demonstrated in all eukaryotes except plants, although components of a putative plant pathway have been characterized. To evaluate the in vivo capability of plant eIF2alpha to participate in the translation pathway, we have used vaccinia virus recombinants that constitutively express wheat eIF2alpha and inducibly express the eIF2alpha dsRNA-stimulated protein kinase, PKR, in BSC-40 cells. Activation of PKR in cells expressing wild-type wheat eIF2alpha resulted in an inhibition of cellular and viral protein synthesis and an induction of cellular apoptosis correlating with phosphorylation of eIF2alpha on serine 51. Expression of a nonphosphorylatable mutant (51A) of plant eIF2alpha reversed the PKR-mediated translational block as well as the PKR-induced apoptosis. A direct interaction of the plant proteins with the mammalian translational initiation apparatus is supported by coimmunoprecipitation of wild-type plant eIF2alpha and the 51A mutant with mammalian eIF2gamma and the localization of the plant proteins in ribosome fractions. These findings suggest that plant eIF2alpha is capable of interacting with the guanine nucleotide exchange factor eIF2B within the context of the eIF2 holoenzyme and provide direct evidence for its ability to participate in phosphorylation-mediated translational control in vivo.

Amino Acid Sequence↗
PubMed2006

Cloning and characterization of CBL-CIPK signalling components from a legume (Pisum sativum).

The studies on calcium sensor calcineurin B-like protein (CBL) and CBL interacting protein kinases (CIPK) are limited to Arabidopsis and rice and their functional role is only beginning to emerge. Here, we present cloning and characterization of a protein kinase (PsCIPK) from a legume, pea, with novel properties. The PsCIPK gene is intronless and encodes a protein that showed partial homology to the members of CIPK family. The recombinant PsCIPK protein was autophosphorylated at Thr residue(s). Immunoprecipitation and yeast two-hybrid analysis showed direct interaction of PsCIPK with PsCBL, whose cDNA and genomic DNA were also cloned in this study. PsCBL showed homology to AtCBL3 and contained calcium-binding activity. We demonstrate for the first time that PsCBL is phosphorylated at its Thr residue(s) by PsCIPK. Immunofluorescence/confocal microscopy showed that PsCBL is exclusively localized in the cytosol, whereas PsCIPK is localized in the cytosol and the outer membrane. The exposure of plants to NaCl, cold and wounding co-ordinately upregulated the expression of PsCBL and PsCIPK genes. The transcript levels of both genes were also coordinately stimulated in response to calcium and salicylic acid. However, drought and abscisic acid had no effect on the expression of these genes. These studies show the ubiquitous presence of CBL/CIPK in higher plants and enhance our understanding of their role in abiotic and biotic stress signalling.

Amino Acid Sequence↗
PubMedDate not supplied

The role of bacterial biofilms in ocular infections.

There is increasing evidence that bacterial biofilms play a role in a variety of ocular infections. Bacterial growth is characterized as a biofilm when bacteria attach to a surface and/or to each other. This is distinguished from a planktonic or free-living mode of bacterial growth where these interactions are not present. Biofilm formation is a genetically controlled process in the life cycle of bacteria resulting in numerous changes in the cellular physiology of the organism, often including increased antibiotic resistance compared to growth under planktonic conditions. The presence of bacterial biofilms has been demonstrated on many medical devices including intravenous catheters, as well as materials relevant to the eye such as contact lenses, scleral buckles, suture material, and intraocular lenses. Many ocular infections often occur when such prosthetic devices come in contact with or are implanted in the eye. For instance, 56% of corneal ulcers in the United States are associated with contact lens wear. Bacterial biofilms may participate in ocular infections by allowing bacteria to persist on abiotic surfaces that come in contact with, or are implanted in the eye, and by direct biofilm formation on the biotic surfaces of the eye. An understanding of the role of bacterial biofilm formation in ocular infections may aid in the development of future antimicrobial strategies in ophthalmology. We review the current literature and concepts relating to biofilm formation and infections of the eye.

Biofilms↗
PubMed1982

Host-Pathogen Interactions : XXI. Extraction of a Heat-Labile Elicitor of Phytoalexin Accumulation from Frozen Soybean Stems.

An extract of frozen and thawed soybean (Glycine max L. Merr. cv. Wayne) stems is active, in wounded soybean cotyledons, as a heat-labile elicitor of phytoalexins. The elicitor activity of the extract is destroyed by heating to 95 degrees C for 10 minutes. The fraction that contains heat-labile elicitor activity releases heat-stable elicitor-active molecules from purified soybean cell walls. Heat-labile elicitor activity voids a Bio-Gel P-6 column and can be absorbed onto and eluted from a DEAE Sephadex ion exchange column. Using the cotyledon phytoalexin elicitor assay, maximum heatlabile elicitor activity was obtained when soybean stems were extracted with acetate buffer at pH 6.0. Addition of 1 millimolar CaCl(2) increased apparent heat-labile elicitor activity. The heat-labile elicitor stimulated maximum phytoalexin accumulation when applied to cotyledons immediately after the cotyledons were cut. Partially purified stem extracts lost heat-labile elicitor activity during storage for several days at 3 degrees C. The possible role of a heat-labile elicitor in stimulation of phytoalexin accumulation by both abiotic and biotic elicitors is discussed.

Journal Article↗
PubMed2025

Dual localization of JA receptor, CaCOI2, explains JA perception dynamics in chickpea.

Jasmonates (JAs) are a group of oxylipin-derived phytohormones involved in various biotic and abiotic stress responses and regulate plant development. JAs are perceived by receptor proteins called coronatine insensitive (COI). These JA receptors encode F-box proteins that form the SCFCOI ubiquitin ligase complex (comprising Skp, Cullin, and F-box) and activate JA signaling by promoting the degradation of the transcriptional repressor JAZ (JA associated ZIM domain containing) proteins via the 26S proteasomal pathway. However, JA signaling is not well understood in chickpea, a vital legume. In this study, we identified two potential chickpea JA receptors, named CaCOI1 and CaCOI2, and characterized CaCOI2 as a functional JA receptor. Subcellular localization experiments revealed that CaCOI2 is localized outside the nucleus but moves into the nucleus upon JA perception to activate signaling. Using domain-swapping experiments between CaCOI1 and CaCOI2, we demonstrated that the leucine-rich repeat region of the receptors, which interacts with bioactive JA such as JA-Isoleucine, also plays a crucial role in controlling the subcellular localization of CaCOI proteins. Our findings identify a functional JA receptor in chickpea and reveal new aspects of JA signaling and perception, which may also be relevant to other plants.

Cicer↗
PubMed2002

The trouble with sealworms (Pseudoterranova decipiens species complex, Nematoda): a review.

Sealworms or codworms, larvae of ascaridoid nematodes belonging to the Pseudoterranova decipiens species complex, infect the flesh of numerous species of marine and euryhaline fish, and have proven a chronic and costly cosmetic problem for seafood processors. Moreover, the parasite may cause abdominal discomfort in humans when consumed in raw, undercooked or lightly marinated fish. In this review, the phylogeny, life cycle and distributions of sealworms are discussed along with biotic and abiotic factors which may influence distributions of these parasites in their intermediate and final hosts. Also considered here are efforts to control the problem through commercial fishing practices, fish processing technology, and the reduction of infection parameters in marine fish populations by biological means. Ironically, concern over sealworm problem has subsided in some fisheries in recent years, not as a result of falling infection parameters in fish stocks or innovations in processing technology, but as a consequence of declines in abundance and size of groundfish.

Animals↗
PubMed2002

The biotic ligand model: a historical overview.

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.

Animals↗
PubMed2004

Physiological interactions of silver and humic substances in Daphnia magna: effects on reproduction and silver accumulation following an acute silver challenge.

Silver (Ag) in aquatic environments mediates its toxic actions by inhibiting sodium influx. Humic substances protect against silver toxicity by complexing the toxic, ionic form of the metal, but may also directly stimulate sodium influx in aquatic organisms. This study investigated the effects of silver and humic substances on the water flea Daphnia magna. Acute silver challenge (24 h; 1 microg L(-1)) and the chronic exposure to humic substances (Aldrich humic acid; 7 mg C L(-1)) had considerable influence on daphnid physiology and reproduction. In particular silver exposure in the absence of humic substances stimulated reproduction, resulted in enhanced adult mass, and altered both the response of the animal to subsequent silver exposure and a physiological surrogate measure of silver toxicity (whole body sodium concentration). The presence of humic substances countered the effects on adult mass and reproduction, returning these parameters to control levels. Humic substances also lowered silver body burden, but with significantly improved whole body sodium status than previously silver-exposed animals. These changes may distort the correlation between silver body burden and indicators of toxic action, an important tenet of site-specific risk assessment tools such as the biotic ligand model.

Animals↗
PubMed2005

Predicting copper toxicity in estuarine and marine waters using the Biotic Ligand Model.

The Biotic Ligand Model (BLM) has proven efficient in predicting the toxicity of a variety of metals to freshwater organisms. Consequently, the US EPA has proposed its use for calculating freshwater copper criteria. This study evaluates the BLM for use in estuarine and marine waters. Studies were conducted using the bivalve, Mytilus sp. and 48-h embryo-larval development chronic estimator test methods. These are the most sensitive taxa and test in the US EPA saltwater copper criteria database. Samples from five locations around the USA were tested. There is a strong relationship between measured and BLM predicted copper EC50s (log transformed data, r(2)=0.76, p<0.001, n=44). The BLM predicted within a factor +/-2 of measured EC50s in 41 of 44 cases. However, the BLM tends to predict lower EC50s when measured EC50s are approximately < or =10 microg Cu/L. This may be due to limitations of the metal-dissolved organic matter interaction model.

Animals↗
PubMed2006

Temporal variation in plant-soil feedback controls succession.

Soil abiotic and biotic factors play key roles in plant community dynamics. However, little is known about how soil biota influence vegetation changes over time. Here, we show that the effects of soil organisms may depend on both the successional development of ecosystems and on the successional position of the plants involved. In model systems of plants and soils from different successional stages, we observed negative plant-soil feedback for early-successional plant species, neutral feedback for mid-successional species, and positive feedback for late-successional species. The negative feedback of early-successional plants was independent of soil origin, while late-successional plants performed best in late- and worst in early-successional soil. Increased performance of the subordinate, late-successional plants resulted in enhanced plant community diversity. Observed feedback effects were more related to soil biota than to abiotic conditions. Our results show that temporal variations in plant-soil interactions profoundly contribute to plant community assemblage and ecosystem development.

Biodiversity↗
PubMed2026

Comprehensive transcriptomic analysis of BjGL1-knockout Brassica juncea: novel insights into leaf trichome formation.

Brassica juncea is a common cruciferous crop, which can be used not only for oil extraction but also as condiments and medicinal materials. It is regarded by both traditional medicine and modern nutrition science as a food with combined dietary and health promoting value. Leaf trichomes are hair-like structures differentiated from epidermal cells and constitute an important barrier against biotic and abiotic stresses, playing a crucial role in enhancing plant resistance and thus possessing significant scientific relevance. In this study, the phenotype and gene editing site of BjA06.GL1 and BjB02.GL1 knockout mustard T1 generation plants were identified. Then, RNA sequencing was performed to compare the leaf transcriptome profiles between gene-edited lines and wild-type plants, with the aim of elucidating the molecular regulatory mechanisms by which BjGL1 controls leaf trichome development and associated biological processes in mustard. The sequencing data showed that, on average, 90.64% of the reads uniquely aligned to the Brassica juncea (Xuecai) reference genome. A total of 4,604 differentially expressed genes were identified in this study. Compared with the gene knockout mutant, 1,831 genes were significantly upregulated and 2,773 genes were downregulated in mustard leaves with trichomes. The differentially expressed genes were mainly enriched in pathways related to cytochrome P450 (CYP), transporters, environmental adaptation, and plant-pathogen interactions. These pathways are closely associated with secondary metabolite biosynthesis, transmembrane transport, and responses to abiotic stress and pathogen defense. qRT-PCR validation confirmed consistent expression trends of trichome regulatory genes screened from transcriptome data. This study provides an important theoretical basis for elucidating molecular mechanisms potentially contributing to trichome formation in mustard.

Mustard Plant↗
PubMed2006

A cDNA microarray approach to decipher sunflower (Helianthus annuus) responses to the necrotrophic fungus Phoma macdonaldii.

To identify the genes involved in the partial resistance of sunflower (Helianthus annuus) to the necrotrophic fungus Phoma macdonaldii, we developed a 1000-element cDNA microarray containing carefully chosen genes putatively involved in primary metabolic pathways, signal transduction and biotic stress responses. A two-pass general linear model was used to normalize the data and then to detect differentially expressed genes. This method allowed us to identify 38 genes differentially expressed among genotypes, treatments and times, mainly belonging to plant defense, signaling pathways and amino acid metabolism. Based on a set of genes whose differential expression was highly significant, we propose a model in which negative regulation of a dual-specificity MAPK phosphatase could be implicated in sunflower defense mechanisms against the pathogen. The resulting activation of the MAP kinase cascade could subsequently trigger defense responses (e.g. thaumatin biosynthesis and phenylalanine ammonia lyase activation), under the control of transcription factors belonging to MYB and WRKY families. Concurrently, the activation of protein phosphatase 2A (PP2A), which is implicated in cell death inhibition, could limit pathogen development. The results reported here provide a valuable first step towards the understanding and analysis of the P. macdonaldii-sunflower interaction.

Ascomycota↗