Endozoochorous seed dispersal by cattle and horse in a spatially heterogeneous landscape

Seed dispersal has become an important issue in plant ecology and restoration management. In this paper we examined dung germinating seed content and seed deposition patterns of horses (Shetland and Konik breeds) and Scottish Highland cattle grazing two coastal dune nature reserves. Two times 2.5 l of fresh dung from each type of herbivore were collected during seven sessions in the main fruiting season. Dung samples were placed under greenhouse conditions after drying and cooling. Animal defecation patterns were derived from a study of herbivore activities during 6 h observation sessions 8 times a month. One hundred and seventeen plant species i.e. 27% of all species occurring in the study area, were recorded as seedlings emerging from the dung samples. The most abundantly and frequently recorded plant species were Urtica dioica, Juncus spp. and different species of Poaceae and Caryophyllaceae. In general seedling density is high (1158 seedlings/dung sample). Seedling density and species richness were further analysed in order to detect temporal variability and possible animal and site related characteristics. Dung deposition patterns reflect a non-random use of habitats and hence a non-random seed deposition among habitats. Calculated seed deposition per square meter ranged from a few (<10 germinating seeds) to more than 100 in the most frequently selected habitats. From the herbivores’ selective habitat use and their estimated mean retention time we can further assume their ability for inter-habitat endozoochorous seed dispersal. This characteristic of large herbivores is further discussed in the light of nature management and restoration.Indra Lamoot is an aspirant of FWO-Flanders.     

GCP-2/CXCL6 synergizes with other endothelial cell-derived chemokines in neutrophil mobilization and is associated with angiogenesis in gastrointestinal tumors

The precise role of chemokines in neovascularization during inflammation or tumor growth is not yet fully understood. We show here that the chemokines granulocyte chemotactic protein-2 (GCP-2/CXCL6), interleukin-8 (IL-8/CXCL8), and monocyte chemotactic protein-1 (MCP-1/CCL2) are co-induced in microvascular endothelial cells after stimulation with pro-inflammatory stimuli. In contrast with its weak proliferative effect on endothelial cells, GCP-2 synergized with MCP-1 in neutrophil chemotaxis. This synergy may represent a mechanism for tumor development and metastasis by providing efficient leukocyte infiltration in the absence of exogenous immune modulators. To mimic endothelial cell-derived GCP-2 in vivo, GCP-2 was intravenously injected and shown to provoke a dose-dependent systemic response, composed of an immediate granulopenia, followed by a profound granulocytosis. By immunohistochemistry, GCP-2 was further shown to be expressed by endothelial cells from human patients with gastrointestinal (GI) malignancies. GCP-2 staining correlated with leukocyte infiltration into the tumor and with the expression of the matrix metalloproteinase-9 (MMP-9/gelatinase B). Together with previous findings, these data suggest that the production of GCP-2 by endothelial cells within the tumor can contribute to tumor development through neovascularization due to endothelial cell chemotaxis and to tumor cell invasion and metastasis by attracting and activating neutrophils loaded with proteases that promote matrix degradation.     

Spatiotemporal allozyme variation in the damselfly, <Emphasis Type="BoldItalic">Lestes viridis</Emphasis> (Odonata: Zygoptera): gene flow among permanent and temporary ponds

Several insect species seem to persist not only in permanent but also in temporary ponds where they face particularly harsh conditions and frequent extinctions. Under such conditions, gene flow may prevent local adaptation to temporary ponds and may promote phenotypic plasticity, or maintain apparent population persistence. The few empirical studies on insects suggest the latter mechanism, but no studies so far quantified gene flow including both pond types. We investigated the effects of pond type and temporal variation on population genetic differentiation and gene flow in the damselfly Lestes viridis in northern Belgium. We report a survey of two allozyme loci (Gpi, Pgm) with polyacrylamide gel electrophoresis in 14 populations from permanent and temporary ponds, and compared these results with similar data from the same permanent populations one year before. The data suggested that neither pond-drying regime, nor temporal variation have a substantial effect on population genetic structuring and did not provide evidence for stable population differentiation in L. viridis in northern Belgium. Gene flow estimates were high within permanent and temporary ponds, and between pond types. Our data are consistent with a source-sink metapopulation system where temporary ponds act as sinks in dry years, and are quickly recolonized after local population extinction. This may create a pattern of apparent population persistence of this species in permanent and temporary ponds without clear local adaptation.     

Apoptosis signal regulating kinase-1 connects reactive oxygen species to p38 MAPK-induced mitochondrial apoptosis in UVB-irradiated human keratinocytes

The p38 MAPK pathway controls critical premitochondrial events culminating in apoptosis of UVB-irradiated human keratinocytes, but the upstream mediators of this stress signal are not completely defined. This study shows that in human keratinocytes exposed to UVB the generation of reactive oxygen species (ROS) acts as a mediator of apoptosis signal regulating kinase-1 (Ask-1), a redox-sensitive mitogen-activated protein kinase kinase kinase (MAP3K) regulating p38 MAPK and JNK cascades. The NADPH oxidase antagonist diphenylene iodonium chloride and the EGFR inhibitor AG1487 prevent UVB-mediated ROS generation, the activation of the Ask-1-p38 MAPK stress response pathway, and apoptosis, evidencing the link existing between the early plasma membrane-generated ROS and the activation of a lethal cascade initiated by Ask-1. Consistent with this, Ask-1 overexpression considerably sensitizes keratinocytes to UVB-induced mitochondrial apoptosis. Although the JNK pathway is also stimulated after UVB, the killing effect of Ask-1 overexpression is reverted by p38 MAPK inhibition, suggesting that Ask-1 exerts its lethal effects mainly through the p38 MAPK pathway. Moreover, p38alpha(-/-) murine embryonic fibroblasts are protected from UVB-induced apoptosis even if JNK activation is fully preserved. These results argue for an important role of the UVB-generated ROS as mediators of the Ask-1-p38 MAPK pathway that, by culminating in apoptosis, restrains the propagation of potentially mutagenic keratinocytes.     

Comparison of lentiviral vector titration methods

Background  

Lentiviral vectors are efficient vehicles for stable gene transfer in dividing and non-dividing cells. Several improvements in vector design to increase biosafety and transgene expression, have led to the approval of these vectors for use in clinical studies. Methods are required to analyze the quality of lentiviral vector production, the efficiency of gene transfer and the extent of therapeutic gene expression.     

Understanding the development of roots exposed to contaminants and the potential of plant-associated bacteria for optimization of growth

Background and Scope

Plant responses to the toxic effects of soil contaminants, such as excess metals or organic substances, have been studied mainly at physiological, biochemical and molecular levels, but the influence on root system architecture has received little attention. Nevertheless, the precise position, morphology and extent of roots can influence contaminant uptake. Here, data are discussed that aim to increase the molecular and ecological understanding of the influence of contaminants on root system architecture. Furthermore, the potential of plant-associated bacteria to influence root growth by their growth-promoting and stress-relieving capacities is explored.

Methods

Root growth parameters of Arabidopsis thaliana seedlings grown in vertical agar plates are quantified. Mutants are used in a reverse genetics approach to identify molecular components underlying quantitative changes in root architecture after exposure to excess cadmium, copper or zinc. Plant-associated bacteria are isolated from contaminated environments, genotypically and phenotypically characterized, and used to test plant root growth improvement in the presence of contaminants.

Key Results

The molecular determinants of primary root growth inhibition and effects on lateral root density by cadmium were identified. A vertical split-root system revealed local effects of cadmium and copper on root development. However, systemic effects of zinc exposure on root growth reduced both the avoidance of contaminated areas and colonization of non-contaminated areas. The potential for growth promotion and contaminant degradation of plant-associated bacteria was demonstrated by improved root growth of inoculated plants exposed to 2,4-di-nitro-toluene (DNT) or cadmium.

Conclusions

Knowledge concerning the specific influence of different contaminants on root system architecture and the molecular mechanisms by which this is achieved can be combined with the exploitation of plant-associated bacteria to influence root development and increase plant stress tolerance, which should lead to more optimal root systems for application in phytoremediation or safer biomass production.