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At least 397 records · Page 22Linked to original sources
PubMed2006

Effects of competition on the fitness of wild and crop-wild hybrid sunflower from a diversity of wild populations and crop lines.

Gene flow between crop fields and wild populations often results in hybrids with reduced fitness compared to their wild counterparts due to characteristics imparted by the crop genome. But the specifics of the evolutionary outcome of crop-wild gene flow may depend on context, varying due to local environmental conditions and genetic variation within and among wild populations and among crop lines. To evaluate context-dependence of fitness of F1 hybrids, sunflower crop lines were crossed with nine wild populations from across the northern United States. These crop-wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Hybrids were far less fecund than wild plants, yet more likely to survive to reproduce. There was considerable variability among wild populations for fecundity and the specific crop line used to generate the crop-wild hybrid significantly affected fecundity. The fitness deficit suffered by crop-wild hybrids varied by population, as did the rankings of the crop-wild hybrids from three different crop lines. Wheat competition decreased fecundity and survival considerably and hampered seed production of wild plants more than that of hybrids. Genotype x environment interactions indicated that the response of fitness to competition differed by population. Consequently, the fitness of hybrids relative to wild plants varied considerably among wild populations and was not consistent across environments. Notably, relative fitness of hybrids was greater under competitive conditions. This research is the first study of its kind to demonstrate that the consequences of crop-wild gene flow are context dependent and contingent on the genetics of the specific wild populations and the local biotic and abiotic conditions.

Biodiversity↗
PubMed2003

Ecological effects of sulfur dioxide, fluorides, and minor air pollutants: recent trends and research needs.

The regulation of the emissions of 'traditional' primary air pollutants (fluorides, sulfur dioxide) has changed the pattern of exposure of ecological systems, with greatly reduced exposure close to sources, but with a smaller effect in some remote areas. Measurements show that recovery is occurring at some sites, in fresh water chemistry (reduced acidity) and in sensitive biota (sustainable fish populations). However, the pattern of change in exposure has not always been simply related to emission reductions. An understanding of responses to recent changes will improve our predictions of the response to future emission changes, both locally and globally. As exposure to 'traditional' pollutants is reduced, the potential for other pollutants to have effects becomes more evident. In the aqueous phase, we need to understand the role of soluble and suspended organics, but this also means explicit recognition of the possibility of phase exchange, and the role of photolytic reactions on plant, soil, and water surfaces. Do highly reactive free radicals in the atmosphere, formed by the action of sunlight on volatile organic compounds, have direct effects on plants? Organic compounds and heavy metals may be bioactive as gases and particles, but for many potentially toxic compounds, the experimental evidence for biotic response is very limited. To evaluate the potential effects of pollutants, we need to understand the pathways by which airborne pollutants enter and react within ecosystems. For vegetation, we have to consider bidirectional fluxes, and distinguish among uptake through stomata, through leaf surfaces, or through roots. There are several challenges for the future. (1) Can we devise experiments that permit exposure of vegetation to gases, particles, and/or aqueous pollutants at 'realistic' concentrations? (2) Can we include the potential interactions with photolytically derived free radicals, and the dynamics of exchange? (3) How do we allow for responses to pollutant mixtures, or the simultaneous exposure to pollutants in gas, particle, and aqueous phases? The recognition of the importance of the dynamic exchange of pollutants between phases will be the key to the development of effective experimental approaches to evaluating cause-effect relationships between pollutant mixtures and ecosystem responses.

Air Pollutants↗
PubMedDate not supplied

Plant phenology in western Canada: trends and links to the view from space.

One feature of climate change is the trends to earlier spring onset in many north temperate areas of the world. The timing of spring flowering and leafing of perennial plants is largely controlled by temperature accumulation; both temperature and phenological records illustrate changes in recent decades. Phenology studies date back over a century, with extensive databases existing for western Canada. Earlier spring flowering has been noted for many woody plants, with larger trends seen for species that develop at spring's start. Implications for ecosystems of trends to earlier spring arrival include changes in plant species composition, changes in timing and distribution of pests and disease, and potentially disrupted ecological interactions. While Alberta has extensive phenology databases (for species, years, and geographic coverage) for recent decades, these data cannot provide continuous ground coverage. There is great potential for phenological data to provide ground validation for satellite imagery interpretation, especially as new remote sensors are becoming available. Phenological networks are experiencing a resurgence of interest in Canada (www.plantwatch.ca) and globally, and linking these ground-based observations with the view from space will greatly enhance our capacity to track the biotic response to climate changes.

Canada↗
PubMed2004

Using multiple metal-gill binding models and the toxic unit concept to help reconcile multiple-metal toxicity results.

Metal-gill binding models and biotic ligand models (BLMs) in general are designed to predict metal toxicity to aquatic organisms. These models calculate the amount of a metal-binding to a sensitive biological membrane, such as a fish gill, which equates with metal toxicity. Cation competition at the metal-binding site and anionic complexation in the water decrease metal-binding to the membrane, decreasing metal toxicity. These models have, to date, been developed for individual metals. To assess how these models handle multiple-metal interactions, metal-gill binding models for two to six metals were created and their behavior tested against the toxic unit (TU) concept assuming strict additivity. The multiple-metal models yield greater than strict additivity at low aqueous metal concentrations (Sigma < 1 TU), strict additivity at intermediate metal concentrations (Sigma = 1 TU), and less than strict additivity at high metal concentrations (Sigma > 1 TU), independent of the combination of metals. Deviations from strict additivity are due to the non-linear nature of the models, where greater than linear filling of binding sites occurs at low metal concentrations, and where strong competition for binding sites occurs at high metal concentrations, with a point of strict additivity between, where the metals sum to one toxic unit. Simulations with natural organic matter (NOM) show similar trends but are complex. Mathematical modeling of multiple-metal interactions may help in the interpretation of toxicity results from mixed-metal exposures to aquatic organisms.

Animals↗
PubMed1997

Light control of plant development.

To grow and develop optimally, all organisms need to perceive and process information from both their biotic and abiotic surroundings. A particularly important environmental cue is light, to which organisms respond in many different ways. Because they are photosynthetic and non-motile, plants need to be especially plastic in response to their light environment. The diverse responses of plants to light require sophisticated sensing of its intensity, direction, duration, and wavelength. The action spectra of light responses provided assays to identify three photoreceptor systems absorbing in the red/far-red, blue/near-ultraviolet, and ultraviolet spectral ranges. Following absorption of light, photoreceptors interact with other signal transduction elements, which eventually leads to many molecular and morphological responses. While a complete signal transduction cascade is not known yet, molecular genetic studies using the model plant Arabidopsis have led to substantial progress in dissecting the signal transduction network. Important gains have been made in determining the function of the photoreceptors, the terminal response pathways, and the intervening signal transduction components.

Cryptochromes↗
PubMed2002

Convergence and divergence of stress-induced mitogen-activated protein kinase signaling pathways at the level of two distinct mitogen-activated protein kinase kinases.

Plants respond to biotic and abiotic stresses by inducing overlapping sets of mitogen-activated protein kinases (MAPKs) and response genes. To define the mechanisms of how different signals can activate a common signaling pathway, upstream activators of SIMK, a salt stress- and pathogen-induced alfalfa MAPK, were identified. Here, we compare the properties of SIMKK, a MAPK kinase (MAPKK) that mediates the activation of SIMK by salt stress, with those of PRKK, a distantly related novel MAPKK. Although both SIMKK and PRKK show strongest interaction with SIMK, SIMKK can activate SIMK without stimulation by upstream factors. In contrast, PRKK requires activation by an upstream activated MAPKK kinase. SIMKK mediates pathogen elicitor signaling and salt stress, but PRKK transmits only elicitor-induced MAPK activation. Of four tested MAPKs, PRKK activates three of them (SIMK, MMK3, and SAMK) upon elicitor treatment of cells. However, PRKK is unable to activate any MAPK upon salt stress. In contrast, SIMKK activates SIMK and MMK3 in response to elicitor, but it activates only SIMK upon salt stress. These data show that (1) MAPKKs function as convergence points for stress signals, (2) MAPKKs activate multiple MAPKs, and (3) signaling specificity is obtained not only through the inherent affinities of MAPKK-MAPK combinations but also through stress signal-dependent intracellular mechanisms.

Amino Acid Sequence↗
PubMed2005

Dynamic cellular responses in plant-microbe interactions.

Encounters between plant cells and both 'friendly' and 'hostile' microbes (such as those in symbiotic and pathogenic interactions, respectively) trigger a range of highly dynamic plant cellular responses. These include reorganization of the cytoskeleton, organelle translocation, vesicle trafficking, and alterations in subcellular protein localization. Recent progress in this borderland that bridges the fields of plant-microbe interactions and cell biology heralds the transition from descriptive phenomenology to the identification and characterization of key molecules that are involved in these processes. Intriguingly, molecular events that occur in plant cells in response to microbes also take place upon abiotic wounding and during fundamental plant developmental processes, such as the tip growth of pollen, root hairs and trichomes. Thus, elementary 'activity modules' that are required for the generation of cell polarity in plant morphogenesis appear to be re-used in both abiotic and biotic stress response pathways.

Cytoplasmic Vesicles↗
PubMed2006

Linkages between nutrients and assemblages of macroinvertebrates and fish in wadeable streams: implication to nutrient criteria development.

We sampled 240 wadeable streams across Wisconsin for different forms of phosphorus and nitrogen, and assemblages of macroinvertebrates and fish to (1) examine how macroinvertebrate and fish measures correlated with the nutrients; (2) quantify relationships between key biological measures and nutrient forms to identify potential threshold levels of nutrients to support nutrient criteria development; and (3) evaluate the importance of nutrients in influencing biological assemblages relative to other physicochemical factors at different spatial scales. Twenty-three of the 35 fish and 18 of the 26 macroinvertebrate measures significantly correlated (P < 0.05) with at least one nutrient measure. Percentages of carnivorous, intolerant, and omnivorous fishes, index of biotic integrity, and salmonid abundance were fish measures correlated with the most nutrient measures and had the highest correlation coefficients. Percentages of Ephemeroptera-Plecoptera-Trichoptera individuals and taxa, Hilsenhoff biotic index, and mean tolerance value were macroinvertebrate measures that most strongly correlated with the most nutrient measures. Selected biological measures showed clear trends toward degradation as concentrations of phosphorus and nitrogen increased, and some measures showed clear thresholds where biological measures changed drastically with small changes in nutrient concentrations. Our selected environmental factors explained 54% of the variation in the fish assemblages. Of this explained variance, 46% was attributed to catchment and instream habitat, 15% to nutrients, 3% to other water quality measures, and 36% to the interactions among all the environmental variables. Selected environmental factors explained 53% of the variation in macroinvertebrate assemblages. Of this explained variance, 42% was attributed to catchment and instream habitat, 22% to nutrients, 5% to other water quality measures, and 32% to the interactions among all the environmental variables.

Animals↗
PubMed2001

Biotic and abiotic effects on endoparasites infecting Dipodomys and Perognathus species.

Between 1989 and 1998, 3,504 rodents of the genera Dipodomys and Perognathus were collected from 4 permanent collecting sites on the University of New Mexico's Long Term Ecological Research station, located on the Sevilleta National Wildlife Refuge (SNWR), Socorro County. New Mexico. All animals were killed and examined for endoparasites (acanthocephalans, cestodes, coccidia, and nematodes). The present report focuses on 3 endoparasite groups, cestodes, coccidia, and nematodes. Specific analyses address how prevalence changes were related to abiotic factors such as habitat, season, or precipitation, and how prevalence of each parasite species in each host species differed in relation to host age, host sex, host reproductive status, host body mass, host density, parasite-parasite interactions, and host specificity. A logistic regression was used to determine which host characters and which abiotic factors are correlated with a parasite infection. Significant variables for at least half of the parasites include season, site, and winter precipitation. However, no parasite prevalences were correlated, and significant variables were not identical between parasites, indicating that each parasite species varied independently and that no generalizations can be drawn. The parasite prevalences in these rodents on the SNWR vary in independent and complex ways.

Animals↗
PubMed1989

The causes of extinction.

A species may go extinct either because it is unable to evolve rapidly enough to meet changing circumstances, or because its niche disappears and no capacity for rapid evolution could have saved it. Although recent extinctions can usually be interpreted as resulting from niche disappearance, the taxonomic distribution of parthenogens suggests that inability to evolve may also be important. A second distinction is between physical and biotic causes of extinction. Fossil evidence for constant taxonomic diversity, combined with species turnover, implies that biotic factors have been important. A similar conclusion emerges from studies of recent introductions of predators, competitors and parasites into new areas. The term 'species selection' should be confined to cases in which the outcome of selection is determined by properties of the population as a whole, rather than of individuals. The process has been of only trivial importance in producing complex adaptations, but of major importance in determining the distribution of different types of organisms. An adequate interpretation of the fossil record requires a theory of the coevolution of many interacting species. Such a theory is at present lacking, but various approaches to it are discussed.

Animals↗
PubMed2002

Does natural selection organize ecosystems for the maintenance of high productivity and diversity?

Three types of evidence suggest that natural ecosystems are organized for high productivity and diversity: (i) changes not previously experienced by a natural ecosystem, such as novel human disturbances, tend to diminish its productivity and/or diversity, just as 'random' changes in a machine designed for a function usually impair its execution of that function; (ii) humans strive to recreate properties of natural ecosystems to enhance productivity of artificial ones, as farmers try to recreate properties of natural soils in their fields; and (iii) productivity and diversity have increased during the Earth's history as a whole, and after every major biotic crisis. Natural selection results in ecosystems organized to maintain high productivity of organic matter and diversity of species, just as competition among individuals in Adam Smith's ideal economy favours high production of wealth and diversity of occupations. In nature, poorly exploited energy attracts more efficient users. This circumstance favours the opening of new ways of life and more efficient recycling of resources, and eliminates most productivity-reducing 'ecological monopolies'. Ecological dominants tend to be replaced by successors with higher metabolism, which respond to more stimuli and engage in more varied interactions. Finally, increasingly efficient predators and herbivores favour faster turnover of resources.

Animals↗
PubMed2005

Contrasting effects of chloride on the toxicity of silver to two green algae, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii.

Short-term silver toxicity was determined for two freshwater algae, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii, in the presence and absence of chloride. Silver speciation in the exposure media was controlled and algal growth was measured over 6 h. For P. subcapitata, an alga with low Ag uptake fluxes, silver toxicity could be predicted on the basis of the free Ag+ concentration, in the presence or absence of significant complexation by chloride ions, as predicted by the biotic ligand model (BLM). For C. reinhardtii, an alga with high Ag uptake fluxes, silver toxicity was better predicted by the concentration of all labile dissolved Ag species than by free silver, a result that is consistent with diffusion through the unstirred layer surrounding the cell surface being the rate-limiting step in silver uptake. For both species, growth inhibition could be predicted on the basis of the Ag intracellular quota in the presence or absence of chloride, indicating that silver toxicity is a direct result of intracellular accumulation rather than cell surface interactions.

Chlorides↗
PubMed2006

CaWRKY2, a chili pepper transcription factor, is rapidly induced by incompatible plant pathogens.

WRKY family proteins are a class of plant-specific transcription factors involved in stress response signaling pathways. In this study a gene encoding a putative WRKY protein was isolated from a pepper EST database (http://genepool.kribb.re.kr). The cDNA, named Capsicum annuum WRKY2 (CaWRKY2), encodes a putative polypeptide of 548 amino acids, containing two WRKY domains with zinc finger motifs and two potential nuclear localization signals. Northern blot analyses showed that CaWRKY2 mRNA was preferentially induced during incompatible interactions of pepper plants with PMMoV, Pseudomonas syringae pv. syringae 61, and Xanthomonas axonopodis pv. vesicatoria race 3. Furthermore, CaWRKY2 transcripts were strongly induced by wounding and ethephon treatment, whereas only moderate expression was detected following treatment with salicylic acid and jasmonic acid. CaWRKY2 was translocated to the nucleus when a CaWRKY2-smGFP fusion construct was expressed in onion epidermal cells. CaWRKY2 also had transcriptional activation activity in yeast. Taken together our data suggest that CaWRKY2 is a pathogen-inducible transcription factor that may have a role in early defense responses to biotic and abiotic stresses.

Acetates↗
PubMed2002

Activation of three pathogen-inducible promoters of tobacco in transgenic pear (Pyrus communis L.) after abiotic and biotic elicitation.

In order to improve pear resistance against fire blight caused by Erwinia amylovora, a search for promoters driving high-level expression of transgenes specifically in response to this bacterial pathogen has been undertaken. We have examined the ability of hsr203J, str246C and sgd24 tobacco (Nicotiana tabacum L.) promoters to drive expression of the uidA reporter gene in pear. Transgenic pear clones were obtained by Agrobacterium tumefaciens-mediated transformation. Beta-glucuronidase activity was determined quantitatively and qualitatively in these plants grown in vitro using fluorometric and histochemical assays and compared to cauliflower mosaic virus (CaMV) 35S promoter-driven activity. The hsr203J promoter appeared to be very weakly activated following inoculation in pear, which is the converse of the situation in tobacco. The str246C promoter was rapidly activated in pear during compatible and incompatible interactions, by wounding and following the application of several elicitors (capsicein, cryptogein, harpin, salicylic acid and jasmonic acid). The sgd24 promoter, a deletion derivative of str246C, exhibited a low level of expression after bacterial inoculation, was weakly activated by wounding and elicitors, and was not activated by phytohormones (salicylic acid and jasmonic acid). Interestingly, the sgd24 promoter was locally activated in pear, whereas the str246C promoter was activated systemically from the infection site. Taken together, these data show that, although the s tr246C and sgd24 promoters are less active than the CaMV35S promoter in pear, their pathogen-responsiveness would permit them to be used to drive the expression of transgenes to promote bacterial disease resistance.

Bacteria↗
PubMed1996

Bionomic equilibrium of two-species system. I.

The concept of bionomic equilibrium is used to obtain limits of cost per unit effort and maximum value of effort for the joint harvesting of three types of two-species system: (1) a logistic growth model of two ecologically independent species, (2) a logistic growth model of two species that have competitive interactions, and (3) a Lotka-Volterra model of one prey and one predator. In each case, the existence of feasible bionomic equilibrium points and that of partially feasible bionomic equilibrium points are considered separately. First it is shown that cost per unit effort has both upper and lower threshold values if feasible bionomic equilibrium points occur, whereas it has only the upper threshold values if partially feasible bionomic equilibrium points occur. Further, the threshold values depend solely on the catchability coefficients, the selling prices of unit biomasses, and the parameters of the given model, namely the biotic potentials, carrying capacities, etc. Next, it is proven that for the first type of feasible point, if the cost per unit effort is kept under proper threshold values, then corresponding to each such value, the maximum value of the efforts exerted can be calculated in terms of the given parameters only. Moreover, the set of all such maximum values of the efforts for different choices of cost per unit effort is always bounded and the supremum of these maximum efforts is independent of the choice of cost per unit effort.

Animals↗
PubMed2006

[Entomopathogenic nematodes, insects, bacteria and their relationship used in practice].

In the paper are presented entomopathogenic nematodes (EPN) as a vector of bacteria killing insects. Many abiotic and biotic factors influence the survival and the virulence of mentioned organisms. These biological agents of control are used in practice over twenty years. Knowledge about the relationships between EPN-insect-bacteria allow to increase efficacy of treatment used in order to limiting populations of pests. The paper presents a short review of literature data of titled subjects.

Animals↗
PubMed1999

Coexpression of a defensin gene and a thionin-like via different signal transduction pathways in pepper and Colletotrichum gloeosporioides interactions.

The anthracnose fungus, Colletotrichum gloeosporioides, interacts incompatibly with the ripe fruit of pepper (Capsicum annuum). It interacts compatibly with the unripe-mature fruit. We isolated a defensin gene, jl-l, and a thionin-like gene, PepThi, expressed in the incompatible interaction by using an mRNA differential display method. Both genes were developmentally regulated during fruit ripening, organ-specifically regulated, and differentially induced during the compatible and incompatible interactions. Expression of the PepThi gene was rapidly induced in the incompatible-ripe fruit upon fungal infection. The fungus-inducible PepThi gene is highly inducible only in the unripe fruit by salicylic acid. In both ripe and unripe fruit, it was induced by wounding, but not by jasmonic acid. Expression of the jl-l gene is enhanced by jasmonic acid in the unripe fruit but suppressed in the ripe fruit. These results suggest that both small and cysteine-rich protein genes are induced via different signal transduction pathways during fruit ripening to protect the reproductive organs against biotic and abiotic stresses.

Amino Acid Sequence↗
PubMed2006

Unraveling abiotic stress tolerance mechanisms--getting genomics going.

Homeostasis, a set-value for metabolism under optimal conditions, is rarely achieved by plants because of the cost exerted by external stress factors: climatic, biotic, and nutrient imbalances. Among these, stresses caused by abiotic conditions, such as temperature extremes (freezing, cold and heat), water availability (drought and ion excess) and ion toxicity (salinity and heavy metals), have been difficult to dissect because defense responses to abiotic factors require regulatory changes to the activation of multiple genes and pathways. Genomics technologies that have emerged during the past decade have been useful in addressing, in an integrated fashion, the multigenicity of the plant abiotic stress response through genome sequences; cell-, organ-, tissue- and stress-specific transcript collections; transcript, protein and metabolite profiles and their dynamic changes; protein interactions; and mutant screens.

Adaptation, Physiological↗