Manipulating the pathway of ammonia assimilation in transgenic non-legumes and legumes     

Bertrand Hirel  Belinda Phillipson  Erik Murchie  Akira Suzuki  Caroline Kunz  Sylvie Ferrario  Anis Limami  Sylvain Chaillou  Eliane Deleens  Norbert Brugire  Muriel Chaumont-Bonnet  Christine Foyer  Jean-Franois Morot-Gaudry 《植物养料与土壤学杂志》1997,160(2):283-290

In this paper we discuss the ways in which our understanding of the nature of the molecular controls of nitrogen assimilation has been increased by the use of non-leguminous and leguminous plants with genetically-altered capacities for ammonia assimilation. Using tobacco or Lotus as model plants, Glutamine synthetase (GS) and glutamate synthase (GOGAT) activities have been altered by stimulating or inhibiting in an organ- or tissue-specific manner the expression of the corresponding genes. In a few selected examples, the physiological impact of these genetic manipulations has been studied on plants grown under different nitrogen regimes. The use of such genetically-modified plants will allow us to better understand the molecular control of this metabolic pathway. It is also potentially of great importance in agriculture if such internal and stable modifications are beneficial in terms of nitrogen use efficiency, thus avoiding an excessive utilization of fertilizers or herbicides (GS inhibitors). Our current knowledge and prospects for future development are explored.  相似文献   

Patch-occupancy models indicate human activity as major determinant of forest elephant Loxodonta cyclotis seasonal distribution in an industrial corridor in Gabon     

Ralph Buij  William J. McShea  Patrick Campbell  Michelle E. Lee  Francisco Dallmeier  Sylvain Guimondou  Nicaise Guisseougou  Serge Mboumba  James E. Hines  Alfonso Alonso 《Biological conservation》2007,135(2):189-201

The importance of human activity and ecological features in influencing African forest elephant ranging behaviour was investigated in the Rabi-Ndogo corridor of the Gamba Complex of Protected Areas in southwest Gabon. Locations in a wide geographical area with a range of environmental variables were selected for patch-occupancy surveys using elephant dung to assess seasonal presence and absence of elephants. Patch-occupancy procedures allowed for covariate modelling evaluating hypotheses for both occupancy in relation to human activity and ecological features, and detection probability in relation to vegetation density. The best fitting models for old and fresh dung data sets indicate that (1) detection probability for elephant dung is negatively related to the relative density of the vegetation, and (2) human activity, such as presence and infrastructure, are more closely associated with elephant distribution patterns than are ecological features, such as the presence of wetlands and preferred fresh fruit. Our findings emphasize the sensitivity of elephants to human disturbance, in this case infrastructure development associated with gas and oil production. Patch-occupancy methodology offers a viable alternative to current transect protocols for monitoring programs with multiple covariates.  相似文献   

Deep infiltration through a sandy alluvial fan in semiarid Niger inferred from electrical conductivity survey,vadose zone chemistry and hydrological modelling     

Sylvain Massuel  Guillaume Favreau  Marc Descloitres  Yann Le Troquer  Yves Albouy  Bernard Cappelaere 《CATENA》2006

In semiarid southwestern Niger, most of the groundwater recharge is indirect and occurs through endoreic ponds. Elsewhere in the landscape, there is no evidence of deep infiltration, with a possible exception for gullies and alluvial fans on sandy slopes. In order to verify this hypothesis, a detailed geophysical and geochemical survey was conducted on a large, representative mid-slope fan (6 ha). At this site, distributed hydrological modelling conducted over the encompassing endoreic catchment (190 ha) showed high losses of runoff water by infiltration. Electromagnetic mapping and 2-D electrical imaging survey were used to investigate the 35 m deep vadose zone; in addition, 8 boreholes were drilled following the geophysical survey to constrain the interpretation. Variations in apparent electrical conductivity measured in boreholes appear to be mainly linked with changes in the soil solution mineralization. An extrapolation throughout the area shows that apparent electrical conductivity of the ground is systematically lower below channels; this suggests localised leaching through the unsaturated zone. A physically-based, 2-D distributed hydrologic model was used to estimate the amount of surface water loss by infiltration for the 1992–2002 period. Depending on year, infiltrated volumes range from 1000 to 24 000 m³. This represents between 5% and 16% of the runoff that reaches the final outlet of the basin, an endoreic valley bottom pond where recharge to the aquifer has been shown to occur. Because leaching of the vadose zone is observed down to a depth of 10 m below channels, episodic groundwater recharge through sandy mid-slope fans is highly probable during rainy years.  相似文献   

Exposure of Canadian aboriginal peoples to methylmercury     

Brian Wheatley  Sylvain Paradis 《Water, air, and soil pollution》1995,80(1-4):3-11

Aboriginal peoples living a traditional lifestyle are potentially exposed to contaminants, such as methylmercury (MeHg), which bioaccumulate in aquatic ecosystems. A preliminary analysis of testing of Canadian indigenous people for MeHg from 1970 to 1992 is outlined. By December 1992,71,842 tests of 38,571 individuals had been carried out in 514 native communities across Canada. Of these, 8,847 individuals (23%) had blood, or blood equivalent, MeHg levels greater than 20 μg/l and 608 (1.6%) had levels over 100 μg/l. Clinical examinations were offered to all with levels greater than 100 μg/l in blood, but were unable to produce a definitive diagnosis. In an attempt to ascertain fetal exposure, 2,405 umbilical cord blood samples were taken. In about half of these cases the samples were paired with maternal levels. Of the cord samples 523 (21.8%) were found to have levels greater than 20 μg/l, and the highest level was 224 μg/l. The highest maternal level found was 86 μg/l. A discussion of the assessment of risk from exposure to MeHg in this population is presented as are the initial results of the 20 year retrospective analysis including seasonal exposure patterns and trends in exposure levels. Probable future intiatives based on this analysis are noted.  相似文献   

Bioactive indole derivatives from the South Pacific marine sponges Rhopaloeides odorabile and Hyrtios sp     

Longeon A  Copp BR  Quévrain E  Roué M  Kientz B  Cresteil T  Petek S  Debitus C  Bourguet-Kondracki ML 《Marine drugs》2011,9(5):879-888

Indole derivatives including bromoindoles have been isolated from the South Pacific marine sponges Rhopaloeides odorabile and Hyrtios sp. Their structures were established through analysis of mass spectra and 1D and 2D NMR spectroscopic data. Their potential inhibitory phospholipase A₂ (PLA₂), antioxidant and cytotoxic activities were evaluated. The new derivative 5,6-dibromo-l-hypaphorine (9) isolated from Hyrtios sp. revealed a weak bee venom PLA₂ inhibition (IC₅₀ 0.2 mM) and a significant antioxidant activity with an Oxygen Radical Absorbance Capacity (ORAC) value of 0.22. The sesquiterpene aureol (4), also isolated from Hyrtios sp., showed the most potent antioxidant activity with an ORAC value of 0.29.  相似文献   

Coat protein-mediated protection to cucumber mosaic virus infections in cultivated tomato     

Jan Gielen  Tineke Ultzen  Sylvain Bontems  Wouter Loots  Alie van Schepen  Annemarie Westerbroek  Peter de Haan  Mart van Grinsven 《Euphytica》1996,88(2):139-149

Summary Cucumber mosaic virus (CMV) infections rank among the most devastating diseases in the commercial culture of tomato (Lycopersicon esculentum Mill.), for which suitable sources of natural resistance are not available. The concept of pathogen-derived resistance, however, offers an alternate approach to combat plant viral diseases by transformation of crops with nucleotide sequences derived from the viral genome. This report demonstrates the successful application of such a pathogen-derived resistance gene comprising the CMV coat protein (CP) gene, to generate protection to CMV infections in cultivated tomato. Transformation of an inbred tomato line with the CMV CP gene isolated from a subgroup I strain, engendered high levels of protection to various CMV strains, including a virulent strain causing lethal necrosis and a typical subgroup II strain. Moreover, when challenged by natural infection through aphid vectors in open field, levels of protection were largely maintained in hemizygous hybrids. In all, these results demonstrate that synthetic resistance genes based on the CMV CP gene make excellent sources of broad spectrum resistance to CMV infections for introgression into tomato breeding programs.  相似文献   

Physiological, morphological and allocational plasticity in understory deciduous trees: importance of plant size and light availability     

Delagrange S  Messier C  Lechowicz MJ  Dizengremel P 《Tree physiology》2004,24(7):775-784

In a 4-year study, we investigated changes in leaf physiology, crown morphology and whole-tree biomass allocation in seedlings and saplings of shade-tolerant sugar maple (Acer saccharum Marsh.) and intermediate shade-tolerant yellow birch (Betula alleghaniensis Britt.) growing in natural understory light (0.5 to 35% of full sunlight) or in understory light reduced by 50% with shade nets to simulate the effect of gap closure. Leaf physiological parameters were mainly influenced by the light gradient, whereas crown morphological and whole-tree allocational parameters were mainly influenced by tree size. No single physiological, morphological or allocational trait was identified that could explain the difference in shade tolerance between the species. Yellow birch had higher growth rates, biomass allocation to branches and leaf physiological plasticity and lower crown morphological plasticity in unmodified understory light than sugar maple. Sugar maple did not display significant physiological plasticity, but showed variation with tree size in both crown morphology and whole-tree biomass allocation. When sugar maple was small, a greater proportion of whole-tree biomass was allocated to roots. However, physiological differences between the species decreased with decreasing light and most morphological and allocational differences tended to disappear with increasing tree size, suggesting that many species differences in shade-tolerance are expressed mainly during the seedling stage. Understory trees of both species survived for 4 years under shade nets, possibly because of higher plasticity when small and the use of stored reserves when taller.  相似文献   

Expression of genes encoding chalcone synthase, flavanone 3-hydroxylase and dihydroflavonol 4-reductase correlates with flavanol accumulation during heartwood formation in Juglans nigra     

Beritognolo I  Magel E  Abdel-Latif A  Charpentier JP  Jay-Allemand C  Breton C 《Tree physiology》2002,22(5):291-300

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Rainfall simulation to identify the storm-scale mechanisms of gully bank retreat   总被引：1，自引：0，他引：1  

Vincent Chaplot  Jacqueline BrownPhesheya Dlamini  Tarryn EusticeJean-Louis Janeau  Graham JewittSimon Lorentz  Lauren MartinCharmaine Nontokozo-Mchunu  Ernest OakesPascal Podwojewski  Sylvain RevilCornelia Rumpel  Nhlakanipho Zondi 《Agricultural Water Management》2011,98(11):1704-1710

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff), during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h⁻¹ for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m² buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m⁻² h⁻¹. Runoff erosion proved to be the dominant mechanism and amounted to 450 g m⁻² h⁻¹, followed by splash and fall down of aggregates (about 170 g m⁻² h⁻¹). Gully bank retreat occurred at a rate of 0.55 mm h⁻¹ and assuming that the soil bulk density is 1.3 g cm⁻³, this corresponds to a retreat of 8.8 mm y⁻¹. Extrapolations to the watershed level, where about 500 m² of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha⁻¹ y⁻¹. These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm.  相似文献   

Unilateral nephrectomy in 10 cattle     

Vogel SR  Desrochers A  Babkine M  Mulon PY  Nichols S 《Veterinary surgery : VS》2011,40(2):233-239

Objective: To describe clinical and imaging findings, treatment, and long‐term outcome of cattle undergoing unilateral nephrectomy. Study Design: Case series. Animals: Cattle (n=10). Methods: Medical records (January 1991–August 2008) of cattle that had unilateral nephrectomy were reviewed. Follow‐up data were obtained by owner telephone interview. Results: Nephrectomy was performed without surgical complications. Transient increases in blood urea nitrogen and creatinine concentrations occurred after surgery and then returned to, or below, presurgical values in 9 cattle. Nine cows were discharged and 7 rejoined their respective herd as productive animals without long‐term complications. Conclusions: Ultrasonography was the most useful imaging tool for presurgical diagnosis. Based on our follow‐up data, unilateral nephrectomy resulted in few serious short‐term or long‐term complications, and cattle undergoing this procedure are capable of satisfactory growth, reproduction, and milk production after surgery.  相似文献