Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Caterpillar-inspired design and fabrication of a self-walking actuator with anisotropy, gradient, and instant response
    Li, B. ; Du, T. ; Yu, B. ; Gucht, J. van der; Zhou, F. - \ 2015
    Small 11 (2015)28. - ISSN 1613-6810 - p. 3494 - 3501.
    transfer radical polymerization - polyelectrolyte brushes - thin-films - driven - contraction - expansion - bilayers - solvent - devices - systems
    A caterpillar–mimetic bilayer actuator is reported, based on a wrinkled polydimethylsiloxane elastomer decorated with a hydroresponsive polyelectrolyte brush. The actuator can fold ultrafast into complex three-dimensional structures upon a change in relative humidity of the surrounding air. The folding direction is determined by the geometry of the actuator, the orientation of the wrinkles, and the gradient in polymer height on the surface. And some unique structures such as helicoid and gradient can be obtained that are seldom reported in the case of bilayered devices. The adaptive bending movement is very fast, anisotropic, highly efficient, and reversible. When the environmental humidity is repeatedly cycled up and down, the small device walks on a surface with a roughness gradient, which is reminiscent of the muscle-like movements.
    Spatial sorting and range shifts: consequences for evolutionary potential and genetic signature of a dispersal trait
    Cobben, M.M.P. ; Verboom, J. ; Opdam, P.F.M. ; Hoekstra, R.F. ; Jochem, R. ; Smulders, M.J.M. - \ 2015
    Journal of Theoretical Biology 373 (2015). - ISSN 0022-5193 - p. 92 - 99.
    woodpecker dendrocopos-medius - climate-change - wave-front - expanding population - local adaptation - metapopulation - diversity - expansion - edge - extinction
    Species are shifting their ranges under climate change, with genetic and evolutionary consequences. As a result, the spatial distribution of genetic diversity in a species’ range can show a signature of range expansion. This genetic signature takes time to decay after the range stops expanding and it is important to take that lag time into account when interpreting contemporary spatial patterns of genetic diversity. In addition, the return to spatial equilibrium on an ecologically relevant timescale will depend on migration of genetic diversity across the species’ range. However, during a range shift alleles may go extinct at the retracting range margin due to spatial sorting. Here we studied the spatial pattern of genotypes that differ in dispersal rate across the species range before, during and after a range shift, assessed the effect of range retraction on this pattern, and quantified the duration of the ephemeral genetic signature of range expansion for this trait. We performed simulation experiments with an individual-based metapopulation model under several contemporary climate change scenarios. The results show an increase of the number of individuals with high dispersal rate. If the temperature increased long enough the allele coding for low dispersal rate would go extinct. The duration of the genetic signature of range expansion after stabilisation of the species’ distribution lasted up to 1200 generations after a temperature increase for 60 years at the contemporary rate. This depended on the total displacement of the climate optimum, as the product of the rate of temperature increase and its duration. So genetic data collected in the field do not necessarily reflect current selection pressures but can be affected by historic changes in species distribution, long after the establishment of the current species’ range. Return to equilibrium patterns may be hampered by loss of evolutionary potential during range shift.
    Permafrost collapse after shrub removal shifts tundra ecosystem to a methane source
    Nauta, A.L. ; Heijmans, M.M.P.D. ; Blok, D. ; Limpens, J. ; Elberling, B. ; Gallagher, A. ; Li, B. ; Petrov, R.E. ; Maximov, T.C. ; Huissteden, J. van; Berendse, F. - \ 2015
    Nature Climate Change 5 (2015). - ISSN 1758-678X - p. 67 - 70.
    climate-change - arctic tundra - alaska - thaw - expansion - ice
    Arctic tundra ecosystems are warming almost twice as fast as the global average1. Permafrost thaw and the resulting release of greenhouse gases from decomposing soil organic carbon have the potential to accelerate climate warming2, 3. In recent decades, Arctic tundra ecosystems have changed rapidly4, including expansion of woody vegetation5, 6, in response to changing climate conditions. How such vegetation changes contribute to stabilization or destabilization of the permafrost is unknown. Here we present six years of field observations in a shrub removal experiment at a Siberian tundra site. Removing the shrub part of the vegetation initiated thawing of ice-rich permafrost, resulting in collapse of the originally elevated shrub patches into waterlogged depressions within five years. This thaw pond development shifted the plots from a methane sink into a methane source. The results of our field experiment demonstrate the importance of the vegetation cover for protection of the massive carbon reservoirs stored in the permafrost and illustrate the strong vulnerability of these tundra ecosystems to perturbations. If permafrost thawing can more frequently trigger such local permafrost collapse, methane-emitting wet depressions could become more abundant in the lowland tundra landscape, at the cost of permafrost-stabilizing low shrub vegetation.
    A multilevel analysis of fruit growth of two tomato cultivars in response to fruit temperature
    Okello, R.C. ; Visser, P.H.B. de; Heuvelink, E. ; Lammers, M. ; Maagd, R.A. de; Struik, P.C. ; Marcelis, L.F.M. - \ 2015
    Physiologia Plantarum 153 (2015)3. - ISSN 0031-9317 - p. 403 - 418.
    cell-division - size - endoreduplication - arabidopsis - expression - expansion - genotype - plants - genes - cycle
    Fruit phenotype is a resultant of inherent genetic potential in interaction with impact of environment experienced during crop and fruit growth. The aim of this study was to analyze the genetic and physiological basis for the difference in fruit size between a small (‘Brioso’) and intermediate (‘Cappricia’) sized tomato cultivar exposed to different fruit temperatures. It was hypothesized that fruit heating enhances expression of cell cycle and expansion genes, rates of carbon import, cell division and expansion, and shortens growth duration, whereas increase in cell number intensifies competition for assimilates among cells. Unlike previous studies in which whole-plant and fruit responses cannot be separated, we investigated the temperature response by varying fruit temperature using climate-controlled cuvettes, while keeping plant temperature the same. Fruit phenotype was assessed at different levels of aggregation (whole fruit, cell and gene) between anthesis and breaker stage. We showed that: (1) final fruit fresh weight was larger in ‘Cappricia’ owing to more and larger pericarp cells, (2) heated fruits were smaller because their mesocarp cells were smaller than those of control fruits and (3) no significant differences in pericarp carbohydrate concentration were detected between heated and control fruits nor between cultivars at breaker stage. At the gene level, expression of cell division promoters (CDKB2, CycA1 and E2Fe-like) was higher while that of the inhibitory fw2.2 was lower in ‘Cappricia’. Fruit heating increased expression of fw2.2 and three cell division promoters (CDKB1, CDKB2 and CycA1). Expression of cell expansion genes did not corroborate cell size observations.
    Integrated analysis of land use changes and their impacts on agrarian livelihoods in the western highlands of Kenya
    Mutoko, M.C. ; Hein, L.G. ; Bartholomeus, H. - \ 2014
    Agricultural Systems 128 (2014). - ISSN 0308-521X - p. 1 - 12.
    soil fertility management - proximate causes - cover - deforestation - africa - sustainability - expansion - dynamics - district - growth
    Land degradation is affecting rural livelihoods across sub-Saharan Africa. Promoting sustainable land management requires a thorough understanding of land use change drivers, processes and effects. However, in most African countries reliable data for such investigations are missing. We therefore test an integrated approach to analyse land use dynamics, combining remote sensing images, an in-depth quantitative survey, stakeholder interviews and local statistics. We analyse land dynamics and agricultural production over a 25-year period in Vihiga District, Western Kenya. Specifically, we examine how land use has changed in this period, the main drivers for land use change, and the main effects of these changes on agricultural production. Vihiga District is one of the most densely populated rural areas in Africa. We find that the district has undergone rapid land use change in the past 25 years. In particular, there has been a major conversion of forest and bare land to agricultural land use. Often, it is stated that increasing population pressure triggers agricultural intensification; however, we find little evidence of such a process in Vihiga District. Productivity of tea and, to a lesser extent, vegetables increased but the yields of maize and beans, the most common crops, fluctuated around a ton per hectare. Overall, per capita food crop production dropped by 28% during the past two decades. Our study shows that high and increasing population pressures do not necessarily lead to agricultural intensification, and that there is a need to consider more explicitly off-farm income in development and land management policies and projects.
    Impact of light on leaf initiation: a matter of photosynthate availability in the apical bud?
    Savvides, A. ; Ntagkas, N. ; Ieperen, W. van; Dieleman, J.A. ; Marcelis, L.F.M. - \ 2014
    Functional Plant Biology 41 (2014)5. - ISSN 1445-4408 - p. 547 - 556.
    arabidopsis-thaliana - thermal-time - shade-avoidance - air-temperature - young tomato - blue-light - shoot apex - growth - expansion - responses
    Radiation substantially affects leaf initiation rate (LIR), a key variable for plant growth, by influencing the heat budget and therefore the temperature of the shoot apical meristem. The photosynthetically active component of solar radiation (photosynthetic photon flux density; PPFD) is critical for plant growth and when at shade to moderate levels may also influence LIR via limited photosynthate availability. Cucumber and tomato plants were subjected to different PPFDs (2.5–13.2 mol m–2 day–1) and then LIR, carbohydrate content and diel net CO2 uptake of the apical bud were quantified. LIR showed saturating response to increasing PPFD in both species. In this PPFD range, LIR was reduced by 20% in cucumber and by 40% in tomato plants. Carbohydrate content and dark respiration were substantially reduced at low PPFD. LIR may be considered as an adaptive trait of plants to low light levels, which is likely to be determined by the local photosynthate availability. In tomato and cucumber plants, LIR can be markedly reduced at low PPFD in plant production systems at high latitudes, suggesting that models solely based on thermal time may not precisely predict LIR at low PPFD.
    From space and from the ground: determining forest dynamics in settlement projects in the Brazilian Amazon
    Diniz, F.H. ; Kok, K. ; Hott, H.C. ; Hoogstra-Klein, M.A. ; Arts, B.J.M. - \ 2013
    International Forestry Review 15 (2013)3. - ISSN 1465-5489 - p. 442 - 455.
    land-use change - secondary forests - ecuadorian amazon - transition theory - deforestation - cover - reforestation - colonization - biodiversity - expansion
    Deforestation in the Brazilian Amazon has been partially attributed to the establishment of settlement projects. Acknowledging the difficulties in quantifying the rate and patterns of deforestation, the objective of this paper is to determine forest dynamics (deforestation and reforestation) in areas where settlement projects have been established, at multiple levels and using different methods. Using satellite images from 1985 to 2010, a study was conducted in five settlement projects in Pará State, aiming to determine forest dynamics at municipal and settlement levels. At property level, participatory maps were constructed to understand settlers’ perception of forest/non-forest areas. The results show that reforestation is the current process in the municipality and in some settlements. Settlers, however, perceive areas with secondary regrowth as potentially fertile cropland and might deforest again in the future. More research is needed to elucidate whether the observed reforestation will lead to a forest transition or is merely a temporary trend.
    Comparative proteome approach demonstrates that platelet-derived growth factor C and D efficiently induce proliferation while maintaining multipotency of hMSCs.
    Sotoca, A.M. ; Roelofs-Hendriks, J. ; Boeren, S. ; Kraan, P.M. van der; Vervoort, J. ; Zoelen, E.J. van; Piek, E. - \ 2013
    Experimental Cell Research 319 (2013)17. - ISSN 0014-4827 - p. 2649 - 2662.
    mesenchymal stem-cells - nectin-like molecules - bone-marrow - malignant-transformation - quantitative proteomics - adhesion molecules - factor receptors - adherent cells - in-vitro - expansion
    This is the first study that comprehensively describes the effects of the platelet-derived growth factor (PDGF) isoforms C and D during in vitro expansion of human mesenchymal stem cells (hMSCs). Our results show that PDGFs can enhance proliferation of hMSCs without affecting their multipotency. It is of great value to culture and expand hMSCs in a safe and effective manner without losing their multipotency for manipulation and further development of cell-based therapies. Moreover, differential effects of PDGF isoforms have been observed on lineage-specific differentiation induced by BMP2 and Vitamin D3. Based on label-free LC-based quantitative proteomics approach we have furthermore identified specific pathways induced by PDGFs during the proliferation process, showing the importance of bioinformatics tools to study cell function.
    Export-oriented deforestation in Mato Grosso: harbinger or exception for other tropical forests?
    DeFries, R. ; Herold, M. ; Verchot, L. ; Macedo, M.N. ; Shimabukuro, Y. - \ 2013
    Philosophical Transactions of the Royal Society B. Biological sciences 368 (2013)1619. - ISSN 0962-8436 - 8 p.
    land-use - brazilian cerrado - amazon - conservation - transitions - expansion - map
    The Brazilian state of Mato Grosso was a global deforestation hotspot in the early 2000s. Deforested land is used predominantly to produce meat for distal consumption either through cattle ranching or soya bean for livestock feed. Deforestation declined dramatically in the latter part of the decade through a combination of market forces, policies, enforcement and improved monitoring. This study assesses how representative the national-level drivers underlying Mato Grosso's export-oriented deforestation are in other tropical forest countries based on agricultural exports, commercial agriculture and urbanization. We also assess how pervasive the governance and technical monitoring capacity that enabled Mato Grosso's decline in deforestation is in other countries. We find that between 41 and 54 per cent of 2000–2005 deforestation in tropical forest countries (other than Brazil) occurred in countries with drivers similar to Brazil. Very few countries had national-level governance and capacity similar to Brazil. Results suggest that the ecological, hydrological and social consequences of land-use change for export-oriented agriculture as discussed in this Theme Issue were applicable in about one-third of all tropical forest countries in 2000–2005. However, the feasibility of replicating Mato Grosso's success with controlling deforestation is more limited. Production landscapes to support distal consumption similar to Mato Grosso are likely to become more prevalent and are unlikely to follow a land-use transition model with increasing forest cover
    Mapping invasive woody species in coastal dunes in the Netherlands: a remote sensing approach using LIDAR and high-resolution aerial photographs
    Hantson, W.P.R. ; Kooistra, L. ; Slim, P.A. - \ 2012
    Applied Vegetation Science 15 (2012)4. - ISSN 1402-2001 - p. 536 - 547.
    hippophae-rhamnoides l - rosa-rugosa - vegetation - imagery - laser - classifications - encroachment - diversity - expansion - ecosystem
    Questions Does remote sensing improve classification of invasive woody species in dunes, useful for shrub management? Does additional height information and an object-based classifier increase woody species classification accuracy? Location The dunes of Vlieland, one of the Wadden Sea Islands, the Netherlands. Methods Extensive monitoring using optical remote sensing and LIDAR deliver large amounts of high-quality data to observe and manage coastal dunes as a defence against the sea in the Netherlands. Using these additional data could increase the accuracy of vegetation mapping and monitoring in coastal areas. In this study, a remote sensing approach has been developed to deliver detailed and standardized maps of (invasive) woody species in the dunes of Vlieland using multispectral aerial photographs and vegetation height derived from LIDAR. Three classification methods were used: maximum likelihood (ML) classification using aerial photographs, ML classification combined with vegetation heights derived from LIDAR (ML+) and object-based (OB) classification. Results The use of vegetation height from the LIDAR data increased the overall classification accuracy from 39% to 50%, but particularly improved classification of the taller woody species. The object-based classification increased the overall accuracy of the ML+ from 50% to 60%. The object-based results are comparable to human visual analysis while offering automated analysis. Conclusions Overall, the object-based classification delivers detailed maps of the woody species that are useful for management and evaluation of alien and invasive species in dune ecosystems.
    Patterns of amino acid metabolism by proliferating human mesenchymal stem cells
    Higuera, G.A. ; Schop, D. ; Spitters, T.W. ; Dijkhuizen, R. ; Bracke, M. ; Bruijn, J.D. ; Martens, D.E. ; Karperien, M. ; Boxtel, A.J.B. van; Blitterswijk, C.A. van - \ 2012
    Tissue Engineering. Part A 18 (2012)5-6. - ISSN 1937-3341 - p. 654 - 664.
    marrow stromal cells - bone-marrow - in-vitro - antibody-production - cultivation system - mammalian cells - expansion - growth - culture - glutamine
    The nutritional requirements of stem cells have not been determined; in particular, the amino acid metabolism of stem cells is largely unknown. In this study, we investigated the amino acid metabolism of human mesenchymal stem cells (hMSCs), with focus on two questions: Which amino acids are consumed and/or secreted by hMSCs and at what rates? To answer these questions, hMSCs were cultured on tissue culture plastic and in a bioreactor, and their amino acid profile was analyzed. The results showed that the kinetics of hMSCs growth and amino acid metabolism were significantly higher for hMSCs in tissue culture plastic than in the bioreactor. Despite differences in culture conditions, 8 essential and 6 nonessential amino acids were consumed by hMSCs in both tissue culture plastic and bioreactor cultures. Glutamine was the most consumed amino acid with significantly higher rates than for any other amino acid. The metabolism of nonessential amino acids by hMSCs deviated significantly from that of other cell lines. The secretion of alanine, glycine, glutamate, and ornithine by hMSCs showed that there is a strong overflow metabolism that can be due to the high concentrations of amino acids provided in the medium. In addition, the data showed that there is a metabolic pattern for proliferating hMSCs, which can contribute to the design of medium without animal serum for stem cells. Further, this study shows how to implement amino acid rates and metabolic principles in three-dimensional stem cell biology
    The physics of tissue formation with mesenchymal stem cells
    Higuera, G.A. ; Boxtel, A.J.B. van; Blitterswijk, C.A. van; Moroni, L. - \ 2012
    Trends in Biotechnology 30 (2012)11. - ISSN 0167-7799 - p. 583 - 590.
    bone-marrow - chondrogenic differentiation - mechanical-properties - bioreactor system - shear-stress - iron-oxide - in-vitro - expansion - proliferation - micro
    Cells react to various forms of physical phenomena that promote and maintain the formation of tissues. The best example of this are cells of musculoskeletal origin, such as mesenchymal stem cells (MSCs), which consistently proliferate or differentiate under cues from hydrostatic pressure, diffusive mass transport, shear stress, surface chemistry, mechanotransduction, and molecular kinetics. To date, no other cell type shows greater receptiveness to macroscopic and microscopic cues, highlighting the acute sensitivity of MSCs and the importance of physical principles in tissue homeostasis. In this review, we describe the literature that has shown how physical phenomena govern MSCs biology and provide insight into the mechanisms and strategies that can spur new biotechnological applications with tissue biology.
    Wrong place, wrong time: climate change-induced range shift across fragmented habitat causes maladaptation and declined population size in a modelled bird species
    Cobben, M.M.P. ; Verboom, J. ; Opdam, P.F.M. ; Hoekstra, R.F. ; Jochem, R. ; Smulders, M.J.M. - \ 2012
    Global Change Biology 18 (2012)8. - ISSN 1354-1013 - p. 2419 - 2428.
    vogels - habitatfragmentatie - klimaatverandering - modellen - birds - habitat fragmentation - climatic change - models - expanding population - genetic diversity - wave-front - metapopulation - mutations - dispersal - evolution - expansion - adaptation - survival
    Many species are locally adapted to decreased habitat quality at their range margins, and therefore show genetic differences throughout their ranges. Under contemporary climate change, range shifts may affect evolutionary processes at the expanding range margin due to founder events. Additionally, populations that are affected by such founder events will, in the course of time, become located in the range centre. Recent studies investigated evolutionary changes at the expanding range margin, but have not assessed eventual effects across the species’ range. We explored the possible influence of range shift on the level of adaptation throughout the species’ total range. For this we used a spatially explicit, individual-based simulation model of a woodland bird, parameterised after the middle spotted woodpecker (Dendrocopus medius) in fragmented habitat. We simulated its range under climate change, and incorporated genetic differences at a single locus that determined the individual's degree of adaptation to optimal temperature conditions. Generalist individuals had a large thermal tolerance but relatively low overall fitness, while climate specialists had high fitness combined with a small thermal tolerance. In equilibrium, the populations in the range centre were comprised of the specialists, while the generalists dominated the margins. In contrast, under temperature increase, the generalist numbers increased at the expanding margin and eventually also occupied the centre of the shifting range, while the specialists were located in the retracting margins. This was caused by founder events and led to overall maladaptation of the species, which resulted in a reduced metapopulation size and thus impeded the species’ persistence. We therefore found no evidence for a complementary effect of local adaptation and range shifts on species’ survival. Instead we showed that founder events can cause local maladaptation which can amplify throughout the species’ range, and, as such, hamper the species’ persistence under climate change
    Mapping the irrigated rice cropping patterns of the Mekong delta, Vietnam through hyper-temporal SPOT NDVI image analysis
    Nguyen, Thi Thu Ha ; Bie, C.A.J.M. de; Ali, A. ; Smaling, E.M.A. ; Hoanh, C.T. - \ 2012
    International Journal of Remote Sensing 33 (2012)2. - ISSN 0143-1161 - p. 415 - 434.
    multitemporal modis images - time-series - agriculture - areas - china - south - classification - expansion - systems - fields
    Successful identification and mapping of different cropping patterns under cloudy conditions of a specific crop through remote sensing provides important baseline information for planning and monitoring. In Vietnam, this information is either missing or unavailable; several ongoing projects studying options with radar to avoid earth observation problems caused by the prevailing cloudy conditions have to date produced only partial successes. In this research, optical hyper-temporal Satellite Pour l'Observation de la Terre (SPOT) VEGETATION (SPOT VGT) data (1998–2008) were used to describe and map variability in irrigated rice cropping patterns of the Mekong delta. Divergence statistics were used to evaluate signature separabilities of normalized difference vegetation index (NDVI) classes generated from the iterative self-organizing data analysis technique algorithm (ISODATA) classification of 10-day SPOT NDVI image series. Based on this evaluation, a map with 77 classes was selected. Out of these 77 mapped classes, 26 classes with prior knowledge that they represent rice were selected to design the sampling scheme for fieldwork and for crop calendar characterization. Using the collected information of 112 farmers’ fields belonging to the 26 selected classes, the map produced provides highly accurate information on rice cropping patterns (94% overall accuracy, 0.93 Kappa coefficient). We found that the spatial distributions of the triple and the double rice cropping systems are highly related to the flooding regime from the Hau and Tien rivers. Areas that are highly vulnerable to flooding in the upper part and those that are saline in the north-western part of the delta mostly have a double rice cropping system, whilst areas in the central and the south-eastern parts mostly have a triple rice cropping system. In turn, the duration of flooding is highly correlated with the decision by farmers to cultivate shorter or longer duration rice varieties. The overall spatial variability mostly coincides with administrative units, indicating that crop pattern choices and water control measures are locally synchronized. Water supply risks, soil acidity and salinity constraints and the anticipated highly fluctuating rice market prices all strongly influence specific farmers’ choices of rice varieties. These choices vary considerably annually, and therefore grown rice varieties are difficult to map. Our study demonstrates the high potential of optical hyper-temporal images, taken on a daily basis, to differentiate and map a high variety of irrigated rice cropping patterns and crop calendars at a high level of accuracy in spite of cloudy conditions
    Broad spectrum late blight resistance in potato differential set plants MaR8 and MaR9 is conferred by multiple stacked R genes
    Kim, H.I. ; Lee, H. ; Jo, K.R. ; Mortazavian, S.M.M. ; Huigen, D.J. ; Evenhuis, A. ; Kessel, G.J.T. ; Visser, R.G.F. ; Vossen, J.H. ; Jacobsen, E. - \ 2012
    Theoretical and Applied Genetics 124 (2012)5. - ISSN 0040-5752 - p. 923 - 935.
    phytophthora-infestans mont - race-specific resistance - solanum-bulbocastanum - berthaultii - expansion - venturii - homolog - cloning - bary - ber
    Phytophthora infestans is the causal agent of late blight in potato. The Mexican species Solanum demissum is well known as a good resistance source. Among the 11 R gene differentials, which were introgressed from S. demissum, especially R8 and R9 differentials showed broad spectrum resistance both under laboratory and under field conditions. In order to gather more information about the resistance of the R8 and R9 differentials, F1 and BC1 populations were made by crossing Mastenbroek (Ma) R8 and R9 clones to susceptible plants. Parents and offspring plants were examined for their pathogen recognition specificities using agroinfiltration with known Avr genes, detached leaf assays (DLA) with selected isolates, and gene-specific markers. An important observation was the discrepancy between DLA and field trial results for Pi isolate IPO-C in all F1 and BC1 populations, so therefore also field trial results were included in our characterization. It was shown that in MaR8 and MaR9, respectively, at least four (R3a, R3b, R4, and R8) and seven (R1, Rpi-abpt1, R3a, R3b, R4, R8, R9) R genes were present. Analysis of MaR8 and MaR9 offspring plants, that contained different combinations of multiple resistance genes, showed that R gene stacking contributed to the Pi recognition spectrum. Also, using a Pi virulence monitoring system in the field, it was shown that stacking of multiple R genes strongly delayed the onset of late blight symptoms. The contribution of R8 to this delay was remarkable since a plant that contained only the R8 resistance gene still conferred a delay similar to plants with multiple resistance genes, like, e.g., cv Sarpo Mira. Using this “de-stacking” approach, many R gene combinations can be made and tested in order to select broad spectrum R gene stacks that potentially provide enhanced durability for future application in new late blight resistant varieties
    The effect of operational conditions on the hydrodynamic characteristics of the sludge bed in UASB reactors
    Leitao, R.C. ; Santaellla, S.T. ; Haandel, A.C. van; Zeeman, G. ; Lettinga, G. - \ 2011
    Water Science and Technology 64 (2011)9. - ISSN 0273-1223 - p. 1935 - 1941.
    afvalwaterbehandeling - geactiveerd slib - anaërobe behandeling - slibzuivering - hydrodynamische dispersie - zuiveringsinstallaties - expansie - retentie - volume - waste water treatment - activated sludge - anaerobic treatment - sludge treatment - hydrodynamic dispersion - purification plants - expansion - retention - volume - settling characteristics - expansion characteristics - granular sludge - volume index - velocity - sewage - settleability - design
    This work aims to evaluate the hydrodynamic properties of the sludge bed of Upflow Anaerobic Sludge Blanket (UASB) reactors based on its settleability and expansion characteristics. The methodologies used for the evaluation of the settleability of aerobic activated sludge, and for the expansibility of a sludge bed of Expanded Granular Sludge Bed reactors and Fluidised Bed Reactors were adapted and applied to the particular characteristics of the sludge of UASB reactors. An easy-to-build experimental set-up was developed to assess the parameters necessary for the equations of settleability and of expansibility. The results obtained from the sludges of seven differently operated reactors show that, for the treatment of low strength wastewater, settleability increased and expansibility decreased at decreased hydraulic retention time, from 6 to 1 h, and/or increased influent concentrations, from 136 to approximately 800 mg chemical oxygen demand/L. The results also show that it is useless to design an UASB reactor with a longer hydraulic retention time to cope with hydraulic shock loads, as a more expansible sludge will develop at such condition.
    Rural to urban land conversion in China — How large is the over-conversion and what are its welfare implications?
    Tan, R. ; Qu, F. ; Heerink, N.B.M. ; Mettepenningen, E. - \ 2011
    China Economic Review 22 (2011)4. - ISSN 1043-951X - p. 474 - 484.
    policy - expansion
    The current system of converting farmland to urban land use in China can be characterized as a hybrid system that combines government controls with market-based transfers. In this paper we argue that this hybrid governance structure causes an over-conversion of farmland from the rural to the urban sector, as compared to a competitivemarket situation, and awelfare reallocation that discriminates against farmland owners.We develop a partial equilibriummodel that can be used to examine the impact of the current hybrid governance structure on the over-conversion of farmland and to analyze the welfare changes for different groups of actors and the resulting net social welfare loss. Using a dataset with detailed information on farmland acquisitions and urban land transactions in Yingtan City in Jiangxi Province, we illustrate how this framework can be applied. Our results indicate an over-conversion of 33.5% of the total converted farmland in this city between 1999 and 2003. The welfare of farmland owners affected by the conversion decreased by 1.38 billion RMB, while the net social welfare loss equaled more than 270 million RMB during the same period. The local government obtained 380 million RMB of revenues by reselling farmland as urban land through competitive conveyance mechanisms between 2002 and 2005,while themanufacturing sector gained an estimated 280 million RMB from buying land use rights at relatively low prices. We conclude that the current policy of increasing urban land conveyance through competitive mechanisms does not address two major underlying causes of over-conversion, and that protection of farmlandwould be better served by replacing the current hybrid rural to urban land market structure by a competitive land market.
    Golgi body motility in the plant cell cortex correlates with actin cytoskeleton organization
    Akkerman, M. ; Overdijk, O. ; Schel, J.H.N. ; Emons, A.M.C. ; Ketelaar, T. - \ 2011
    Plant and Cell Physiology 52 (2011)10. - ISSN 0032-0781 - p. 1844 - 1855.
    arabidopsis root hairs - nod factors induce - class-xi myosins - cortical microtubules - latrunculin b - pollen-tube - growth - elongation - expansion - reveals
    The actin cytoskeleton is involved in the transport and positioning of Golgi bodies, but the actin-based processes that determine the positioning and motility behavior of Golgi bodies are not well understood. In this work, we have studied the relationship between Golgi body motility behavior and actin organization in intercalary growing root epidermal cells during different developmental stages. We show that in these cells two distinct actin configurations are present, depending on the developmental stage. In small cells of the early root elongation zone, fine filamentous actin (F-actin) occupies the whole cell, including the cortex. In larger cells in the late elongation zone that have almost completed cell elongation, actin filament bundles are interspersed with areas containing this fine F-actin and areas without F-actin. Golgi bodies in areas with the fine F-actin exhibit a non-directional, wiggling type of motility. Golgi bodies in areas containing actin filament bundles move up to 7 µm s-1. Since the motility of Golgi bodies changes when they enter an area with a different actin configuration, we conclude that the type of movement depends on the actin organization and not on the individual organelle. Our results show that the positioning of Golgi bodies depends on the local actin organization
    The response of Arctic vegetation to the summer climate: relation between shrub cover, NDVI, surface albedo and temperature
    Blok, D. ; Schaepman-Strub, G. ; Bartholomeus, H. ; Heijmans, M.M.P.D. ; Maximov, T.C. ; Berendse, F. - \ 2011
    Environmental Research Letters 6 (2011)3. - ISSN 1748-9326 - 9 p.
    northern alaska - tundra vegetation - siberian tundra - feedbacks - ecosystems - expansion - exchange - trends - forest - map
    Recently observed Arctic greening trends from normalized difference vegetation index (NDVI) data suggest that shrub growth is increasing in response to increasing summer temperature. An increase in shrub cover is expected to decrease summer albedo and thus positively feed back to climate warming. However, it is unknown how albedo and NDVI are affected by shrub cover and inter-annual variations in the summer climate. Here, we examine the relationship between deciduous shrub fractional cover, NDVI and albedo using field data collected at a tundra site in NE Siberia. Field data showed that NDVI increased and albedo decreased with increasing deciduous shrub cover. We then selected four Arctic tundra study areas and compiled annual growing season maximum NDVI and minimum albedo maps from MODIS satellite data (2000–10) and related these satellite products to tundra vegetation types (shrub, graminoid, barren and wetland tundra) and regional summer temperature. We observed that maximum NDVI was greatest in shrub tundra and that inter-annual variation was negatively related to summer minimum albedo but showed no consistent relationship with summer temperature. Shrub tundra showed higher albedo than wetland and barren tundra in all four study areas. These results suggest that a northwards shift of shrub tundra might not lead to a decrease in summer minimum albedo during the snow-free season when replacing wetland tundra. A fully integrative study is however needed to link results from satellite data with in situ observations across the Arctic to test the effect of increasing shrub cover on summer albedo in different tundra vegetation types.
    Compenserende maatregelen in 2009 voor steenuilen in de Waalsprong bij Nijmegen : overzicht van de compenserende en mitigerende maatregelen ter compensatie van het verdwijnen van nest- en foerageergelegenheid voor steenuilen in de Waalsprong
    Blitterswijk, H. van; Jacobs, F.H.H. ; Jagers op Akkerhuis, G.A.J.M. - \ 2011
    Wageningen : Alterra (Alterra-rapport 1971) - 22
    uilen - wildbescherming - natuurbeschermingsrecht - natuurcompensatie - gelderland - nederland - betuwe - expansie - stedelijke gebieden - owls - wildlife conservation - nature conservation law - nature compensation - gelderland - netherlands - betuwe - expansion - urban areas
    Uitbreiding van de stad Nijmegen, ten noorden van de Waal, en maatregelen ter behoud van habitat van roofvogels.
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