Les sols de savanes des llanos vénézuéliens et le sol ferrugineux tropical de Barinas = Los suelos de sabanas de los llanos venezolanos y el alfisol de Barinas

Les savanes constituent une des dernières ressources en terres dont la mise en culture est relativement facile malgré de faibles réserves organiques et minérales qui ne leur assurent qu'un équilibre assez fragile. La station expérimentale du Jardin botanique de l'université expérimentale des Llanos à Barinas sert de cadre depuis 1977 à des expériences effectuées sur un sol ferrugineux tropical lessivé. Le présent travail est consacré à la description : du contexte régional de la station; du profil du sol utilisé en comparaison avec d'autres sols de savanes; de quelques résultats obtenus dans la station et dans la région sur des types de sol voisins. Avant de conclure est discutée la représentativité de la station de Barinas au niveau des savanes en général en vue d'établir la portée des expériences qui y sont ou y seront effectuées. (Résumé d'auteur

Hydrogels for 3D neural tissue models: understanding cell-material interactions at a molecular level.

The development of 3D neural tissue analogs is of great interest to a range of biomedical engineering applications including tissue engineering of neural interfaces, treatment of neurodegenerative diseases and in vitro assessment of cell-material interactions. Despite continued efforts to develop synthetic or biosynthetic hydrogels which promote the development of complex neural networks in 3D, successful long-term 3D approaches have been restricted to the use of biologically derived constructs. In this study a poly (vinyl alcohol) biosynthetic hydrogel functionalized with gelatin and sericin (PVA-SG), was used to understand the interplay between cell-cell communication and cell-material interaction. This was used to probe critical short-term interactions that determine the success or failure of neural network growth and ultimately the development of a useful model. Complex primary ventral mesencephalic (VM) neural cells were encapsulated in PVA-SG hydrogels and critical molecular cues that demonstrate mechanosensory interaction were examined. Neuronal presence was constant over the 10 day culture, but the astrocyte population decreased in number. The lack of astrocytic support led to a reduction in neural process outgrowth from 24.0 ± 1.3 μm on Day 7 to 7.0 ± 0.1 μm on Day 10. Subsequently, purified astrocytes were studied in isolation to understand the reasons behind PVA-SG hydrogel inability to support neural network development. It was proposed that the spatially restrictive nature (or tight mesh size) of PVA-SG hydrogels limited the astrocytic actin polymerization together with a cytoplasmic-nuclear translocation of YAP over time, causing an alteration in their cell cycle. This was confirmed by the evaluation of p27/Kip1 gene that was found to be upregulated by a twofold increase in expression at both Days 7 and 10 compared to Day 3, indicating the quiescent stage of the astrocytes in PVA-SG hydrogel. Cell migration was further studied by the quantification of MMP-2 production that was negligible compared to 2D controls, ranging from 2.7 ± 2.3% on Day 3 to 5.3 ± 2.9% on Day 10. This study demonstrates the importance of understanding astrocyte-material interactions at the molecular level, with the need to address spatial constraints in the 3D hydrogel environment. These findings will inform the design of future hydrogel constructs with greater capacity for remodeling by the cell population to create space for cell migration and neural process extension

Genetic Mouse Models as In Vivo Tools for Cholangiocarcinoma Research

Cholangiocarcinoma (CCA) is a genetically and histologically complex disease with a highly dismal prognosis. A deeper understanding of the underlying cellular and molecular mechanisms of human CCA will increase our current knowledge of the disease and expedite the eventual development of novel therapeutic strategies for this fatal cancer. This endeavor is effectively supported by genetic mouse models, which serve as sophisticated tools to systematically investigate CCA pathobiology and treatment response. These in vivo models feature many of the genetic alterations found in humans, recapitulate multiple hallmarks of cholangiocarcinogenesis (encompassing cell transformation, preneoplastic lesions, established tumors and metastatic disease) and provide an ideal experimental setting to study the interplay between tumor cells and the surrounding stroma. This review is intended to serve as a compendium of CCA mouse models, including traditional transgenic models but also genetically flexible approaches based on either the direct introduction of DNA into liver cells or transplantation of pre-malignant cells, and is meant as a resource for CCA researchers to aid in the selection of the most appropriate in vivo model system

Quality requirements for cross-border care in Europe: a qualitative study of patients’, professionals’ and healthcare financiers’ views

In the past decade the issue of patient mobility has emerged on the European health policy agenda. Although the volume of patients crossing borders to obtain healthcare is low, it is increasing continuously and, due to its legal, financial and medical implications, has generated considerable interest among health policy and other decision makers. However, there is little information available on the safety and patient-centredness of cross-border care and neither governments nor citizens have an explicit basis for comparing healthcare delivery in Europe. This study investigated the viewpoints of patients, professionals and healthcare financiers on the safety and patient-centredness of cross-border care. Qualitative interviews were carried out during 2005 and early 2006 with 40 patients, 30 professionals (doctors, nurses and managers) and 3 healthcare-financing bodies. Although cross-border care has become a common issue in many European countries, there remain uncertainties on the side of each of the parties addressed-patients, professionals and financiers-with regard to the provision of cross-border care. One of the most striking results of this project is the current lack of research on systematic knowledge on the quality of cross-border care. Many of the issues identified through this research may have a potential impact on the quality and safety of cross-border care and will support further investigation and help shape the health policy agenda on patients crossing borders in European Union countries

Genetic variation and clonal diversity in introduced populations of Mimulus guttatus assessed by genotyping at 62 single nucleotide polymorphism loci

Background: Single nucleotide polymorphisms (SNPs) are increasingly being used to study non-native populations. SNPs are relatively information poor on a per locus basis, but allow genotyping more loci than others markers (e.g., microsatellites) and have the advantage of consistent allele calls between studies.Aims: We investigated the utility of a newly developed set of SNP markers, suitable for high throughput genotyping to characterise genotypic variation and population structure in non-native populations of the facultative clonal herb Mimulus guttatus in the United Kingdom (UK).Methods: We analysed 62 SNP markers and using a high throughput platform genotyped 383 individuals from 10 populations from the native range in North America and 14 populations in the UK.Results: We found wide variation in genotypic diversity within UK populations, indicating reproductive strategies that vary from mostly clonal to mostly sexual. All but one UK population were, on average, more closely related to each other than to North American populations, and the exceptional UK population showed strong affinity to native Alaskan plants.Conclusions: A small number of SNPs can detect patterns of clonality and broad-scale relationships between native and introduced populations. However, elucidating population structure at a finer scale will require genotyping individuals at greater depth

Comparison of micrometeorological techinques for estimating ammonia emission from covered slurry storage and land spreading of cattle slurry

The micrometeorological mass-balance integrated horizontal flux (IHF) technique has been commonly employed for measuring ammonia (NH3) emissions inon-field experiments. However, the inverse-dispersion modeling technique, such as the backward Lagrangian stochastic (bLS) modeling approach, is currently highlighted as offering flexibility in plot design and requiring a minimum number of samplers (Ro et al., 2013). The objective of this study was to make a comparison between the bLS technique with the IHF technique for estimating NH3 emission from flexible bag storage and following landspreading of dairy cattle slurry. Moreover, considering that NH3 emission in storage could have been non uniform, the effect on bLS estimates of a single point and multiple downwind concentration measurements was tested, as proposed by Sanz et al. (2010)

Sugar cane nutrient requirements and the role of atmospheric deposition supplying supplementary fertilization in a Venezuelan sugar cane plantation

RESUMEN La región centro norte de Venezuela está caracterizada por lluvias de naturaleza ácida, cargadas de contaminantes que incluyen nutrientes, debido a la intensa actividad industrial y agrícola de la zona. Esta región presenta a su vez grandes extensiones de plantaciones de caña de azúcar. Una vez que la lluvia pasa por el dosel de bosques o de ecosistemas agrícolas, su composición química cambia, ya sea por absorción, lixiviación o lavado de iones depositados en el dosel. Este documento describe los cambios en la química de las aguas de lluvias después de pasar por el dosel de una plantación de caña de azúcar. En cuatro parcelas de 300 m 2 ubicadas en un área experimental de 4.5 ha, plantadas con Saccharum officinarum, se instalaron colectores de agua de lluvia y de escurrimiento foliar. El estudio corresponde al análisis de crecimiento de la tercera soca del cultivo. El pH del agua de lluvia se incrementa cuando pasa por el dosel. La magnitud de los cambios fue importante y se relacionó parcialmente con las cantidades significativas de cationes que se lavan del dosel. Las entradas de N en el agroecosistema fueron altas (25.25 kg ha 1 a -1 ) como consecuencia de la fertilización y quema local de la caña antes de su cosecha y la actividad industrial (petroquímica y fertilizantes) desarrollada en la zona. Las precipitaciones (húmeda y seca) representan una importante fuente de entradas de nutrientes a la plantación. En el caso de los macronutrientes (N, P y K) las entradas fueron altas y suplen una significativa fracción de los requerimientos del cultivo, lo mismo ocurre en el caso del zinc y del cobre. ABSTRACT As a consequence of high industrial and agricultural activities, acidic rains loaded with pollutants-including nutrients-are characteristic of northern central Venezuela, a region dominated by sugar cane plantations. Canopies of forest and agricultural crops can modify the chemistry of rainfall through uptake, leaching and outwash of deposited ions. This paper describes the change in the chemistry of acid rains after passing through a sugar cane canopy. Four plots of 300 m 2 within a 4.5 ha experimental area, planted with Saccharum officinarum had rain and throughfall collectors installed. The study corresponds to the analysis of the growing season of the third ratoon. The pH of the rain in the agroecosystem increased after passing through the canopy. The magnitudes of the changes were important and partially related to the significant amount of cations leached from the leaves or washed out from dry deposition to the leaves. N inputs for wet and dry deposition in the agroecosystem were high (25.25 kg ha -1 yr -1 ) as a consequence of the agricultural activity in the area, the local burning of sugar cane before cropping, and the location of the experimental area close Atmósfera 26(3), 337-348 (2013) 338 D. López-Hernández et al. to petrochemical and fertilizer industries. Rainfall constitutes an important source of nutrient inputs to the sugar cane system. In the case of macronutrients (N, P and K) the inputs were high and supply an important fraction of plant nutrient needs, as occurs for zinc and copper