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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    Optimization of productivity and quality of irrigated tomato (Solanum lycopersicum L.) by smallholder farmers in the Central Rift Valley area of Oromia, Ethiopia
    Gemechis, Ambecha O. - \ 2017
    Wageningen University. Promotor(en): P.C. Struik, co-promotor(en): B. Emana. - Wageningen : Wageningen University - ISBN 9789463431576 - 262
    solanum lycopersicum - irrigation - crop production - optimization - photosynthesis - chlorophyll - gas exchange - water use efficiency - crop yield - ethiopia - solanum lycopersicum - irrigatie - gewasproductie - optimalisatie - fotosynthese - chlorofyl - gasuitwisseling - watergebruiksrendement - gewasopbrengst - ethiopië

    Tomato (Solanum lycopersicum L.) is a vegetable crop with high potential to contribute to poverty reduction via increased income and food security. It is widely grown by smallholders, has high productivity and its demand is increasing. Ethiopia produced about 30,700 Mg of tomatoes on 5,027 ha annually in 2014/2015. Average yields are only 6.1 Mg ha-1, below the world average yields. There is both a need and a potential to increase tomato production per unit area.

    The aim of this thesis is to analyze the irrigated tomato production systems of smallholder farmers in Ethiopia, to survey and characterize the tomato in selected ecoregions and seasons, and to identify yield-limiting or yield-reducing factors and opportunities to enhance yield by using a combination of surveys and field experiments. Field experiments on optimization of yield and quality of field-grown tomato were carried out at Ziway, Ethiopia, for two seasons to study the impact of different irrigation practices applied, based on local empirical practices, deficit irrigation, or crop water requirement.

    This thesis begins with a survey of tomato production systems. The survey details the area and production in various zones and for each of these zones yield- determining, yield-limiting, and yield-reducing factors and opportunities for improving yield and quality are indicated. It also avails area, production and yield data for each growing season and typifies the production systems in these zones. Low temperature (cold) from October-January and shortage of improved seeds are recognized as yield-determining factors, whereas insufficient water and nutrient (fertilizer) supply proved to be yield-limiting factors across zones. Late blight (Phytophthora infestans), Fusarium wilt (Fusarium oxysporum) and different pests and weeds are identified as yield-reducing factors in the zones. Experienced growers who have access to extension service recorded significant yield increment. Farmers Research Groups improved actual average yield with the use of improved technology (improved varieties and quality seed), and better efficiencies of water and fertilizer use. This study quantified influences of irrigation systems and strategies on growth-determining tomato features. Variation in irrigation systems and strategies accounted for variation in growth and dry matter accumulation. Greater performance for yield-related traits was obtained with drip irrigation based on crop water requirement for tomato varieties. Examination of plants showed also that local empirical irrigation is responsible for the occurrence of Phytophthora root rot, whereas deficit irrigation proved cause for occurrence of Fusarium wilt (Fusarium oxysporum), blossom end rot and broome rape (Orobanche ramosa) on roots or leaves, stems or fruits.

    The experiments on irrigation scheduling with different irrigation systems and strategies gave useful indications on the possibility to improve commercial yield (CY) and water use efficiency. Promising results on CY and agronomical water use efficiency of tomato were achieved with drip irrigation based on crop water requirement, while for the biological water use efficiency higher value was obtained with deficit drip irrigation in both seasons. The findings indicate that the CY was decreased significantly for deficit by 50% in drip irrigation and deficit by 50% in furrow irrigation in both seasons. Mean CY for drip irrigation according to crop water requirement increased by 51% and 56% compared with deficit drip irrigation, whereas furrow irrigation based on crop water requirement increased by 52% and 54% compared with deficit furrow in Experiments 1 and 2, respectively. However, water use efficiency decreased with the increasing water volume.

    Simultaneous measurements of rate of photosynthesis based on gas exchange measurements and the thylakoid electron flux based on chlorophyll fluorescence were used to investigate physiological limitations to photosynthesis in leaves of deficit irrigated tomato plants under open field situations. Combined leaf gas exchange/chlorophyll fluorescence measurements differentiated the treatments effectively. Reduction in rate of photosynthesis, stomatal conductance and the maximum quantum efficiency of photosystem II varied across seasons of all varieties, whereas leaf temperature was increased by deficit irrigation in all varieties. Among varieties studied, Miya was found relatively tolerant to deficit irrigation. Stomatal limitation of rate of photosynthesis increased significantly as a result of water stress suggesting a strong influence of the stomatal behaviour.

    We also determined the influence of irrigation systems and strategies on water saving and tomato fruit quality. Using deficit drip irrigation was the best management strategy to optimize water use and tomato quality. Fruit dry matter content, acid content and total soluble solids were significantly higher with deficit drip irrigation than with other treatments.

    From this thesis it appeared that agro-climatic conditions, access to resources and culture all contribute to the relatively low yields of tomato in the Central Rift Valley of Ethiopia. The thesis also proved that significant advances can be made in yield, quality and resource use efficiency.

    Alleen spuiten waar een plant staat, bespaart veel middel : mogelijk met een sensor die bladgroen ‘ziet’
    Os, Erik van; Zande, Jan van de - \ 2016
    horticulture - greenhouse horticulture - plant protection - vegetables - pot plants - cyclamen - tomatoes - spraying equipment - sensors - chlorophyll - sustainability - botrytis - pesticides

    Bij de gang naar een duurzamere tuinbouw ligt de nadruk vaak op vervangen van chemie door biologie. Maar ook bij het spuiten zelf valt nog veel te verbeteren. Als je weet te voorkomen dat grond, tafels of gevels worden meegepakt, bespaar je veel middel en beperk je de emissie. Een stap verder is alleen spuiten op aangetaste delen.

    Natural genetic variation in Arabidopsis thaliana photosynthesis
    Flood, P.J. - \ 2015
    Wageningen University. Promotor(en): Maarten Koornneef, co-promotor(en): Mark Aarts; Jeremy Harbinson. - Wageningen : Wageningen University - ISBN 9789462575004 - 278
    arabidopsis thaliana - genetische variatie - fotosynthese - genomen - chlorofyl - fenotypen - arabidopsis thaliana - genetic variation - photosynthesis - genomes - chlorophyll - phenotypes

    Oxygenic photosynthesis is the gateway of the sun’s energy into the biosphere, it is where light becomes life. Genetic variation is the fuel of evolution, without it natural selection is powerless and adaptation impossible. In this thesis I have set out to study a relatively unexplored field which sits at the intersection of these two topics, namely natural genetic variation in plant photosynthesis. To begin I reviewed the available literature (Chapter 2), from this it became clear that the main bottleneck restricting progress was the lack of high-throughput phenotyping platforms for photosynthesis. To address this an automated high-throughput chlorophyll fluorescence phenotyping system was developed, which could measure 1440 plants in less than an hour for ΦPSII, a measure of photosynthetic efficiency (Chapter 3). Using this phenotyping platform I screened five populations of Arabidopsis thaliana. Three of these populations resulted from bi-parental crosses and segregated for only two genomes, using these I conducted family mapping (Chapter 4). The final two populations were composed of natural, field collected, accessions and were analysed using a genome wide association approach (Chapter 5). The family mapping approach had greater statistical power due to within population replication and the genome wide association approach had higher mapping resolution due to historical recombination. Both approaches were used to identify genomic regions (loci) which were responsible for some of the variation in photosynthesis observed. The number and average effect of these loci was used to infer the genetic architecture of photosynthesis as a highly complex polygenic trait for which there are many loci of very small effect. In addition to screening these large populations a smaller subset of 18 lines was assayed for natural variation in phosphorylation of photosystem II (PSII) proteins in response to changing light (Chapter 6). This exploratory study indicated that this process shows considerable variation and may be important for adaptation of the photosynthetic apparatus to photosynthetic extremes. The genetic mapping studies just described, focus exclusively on genetic variation in the nuclear genome, whilst this contains the majority of the plants genetic information there is also a store of genetic information in the chloroplast and mitochondria. These genetic repositories contain genes which are essential for photosynthesis and energy metabolism. Any variation in these genes could have a large impact on photosynthesis. To study natural variation in these genomes I developed a new population of reciprocal nuclear-organellar hybrids (cybrids) which could be used to study the effect of genetic variation in organelles whilst controlling for nuclear genetic variation (Chapter 7). Preliminary results indicate that this resource will be of great use in disentangling natural genetic variation in nucleo-organelle interactions. Finally I looked at one chloroplast encoded photosynthetic mutation in more detail (Chapter 8). This mutation had evolved in response to herbicide application and had spread along British railways. When studying this population of resistant plants I found empirical evidence for organelle mediated nuclear genetic hitchhiking. This is a previously undescribed evolutionary phenomenon and is likely to be quite common. In conclusion there is an abundance of genetic variation in photosynthesis which can be used to improve the trait for agriculture and provide insights into novel evolutionary phenomena in the field.

    Het effect van licht op bio-aardappel vergroening in de retail
    Pereira da Silva, F.I.D.G. ; Otma, E.C. - \ 2015
    Wageningen : Wageningen UR & Biobased Research (Rapport / Wageningen UR Food & Biobased Research 1528) - ISBN 9789462573635 - 26
    consumptieaardappelen - achteruitgang (deterioration) - vergroening - chlorofyl - kunstlicht - supermarkten - biologische voedingsmiddelen - aardappelen - voedselkwaliteit - table potatoes - deterioration - greening - chlorophyll - artificial light - supermarkets - organic foods - potatoes - food quality
    Uit peilingen van de Nederlandse Aardappel Organisatie en andere, blijkt dat er nog steeds kwaliteitsgebreken vast te stellen zijn bij de biologische aardappels in het schap. Vergroening lijkt één van de belangrijkste aspecten van de kwaliteitsgebreken te zijn. Het doel van dit projectonderdeel is daarom om te onderzoeken welk type licht in de supermarkt leidt tot de beste resultaten om vergroening van bio-aardappels in het schap tegen te gaan.
    Imaging spectroscopy for ecological analysis in forest and grassland ecosystems
    Homolova, L. - \ 2014
    Wageningen University. Promotor(en): Michael Schaepman, co-promotor(en): Jan Clevers. - Wageningen : Wageningen University - ISBN 9789461738240 - 177
    remote sensing - naaldbossen - alpenweiden - picea abies - bladoppervlakte - ecofysiologie - ecosysteemdiensten - vegetatie - chlorofyl - cartografie - beeldvormende spectroscopie - remote sensing - coniferous forests - alpine grasslands - picea abies - leaf area - ecophysiology - ecosystem services - vegetation - chlorophyll - mapping - imaging spectroscopy

    Terrestrial vegetation is an important component of the Earth’s biosphere and therefore playing an essential role in climate regulation, carbon sequestration, and it provides large variety of services to humans. For a sustainable management of terrestrial ecosystems it is essential to understand vegetation responses to various pressures, to monitor and to predict the spatial extent and the rate of ecosystem changes. Remote sensing (RS) therefore offers a unique opportunity for spatially continuous, and for some type of RS data, also frequent monitoring of terrestrial ecosystems.

    RS of vegetation is a broad research field, where a lot of progress has been made in the last three decades. However, the complexity of interactions between vegetation and solar radiation, constantly modulated by environmental factors, offers room for deeper investigation. Rather than solving one big research problem, this thesis built a few bridges on a way leading towards better understanding of using airborne imaging spectroscopy for ecological analysis in temperate coniferous forests and subalpine grasslands. The research was divided into a theoretical and an applied part. The theoretical part contributed to a critical evaluation of research achievements and challenges in optical RS of plant traits (Chapter 2). The applied part addressed three research topics: i) investigating variability of total to projected leaf area ratio in spruce canopies and its implications on RS of chlorophyll content (Chapter 3), ii) testing chlorophyll retrieval methods based on continuum removal in spruce canopies (Chapter 4), and iii) exploring potentials of imaging spectroscopy to map ecosystem properties and the capacity of subalpine grasslands in providing ecosystem services in comparison with a plant trait-based modelling approach (Chapter 5).

    In Chapter 2, we reviewed achievements and challenges in RS estimation of key plant traits and we concentrated our discussion on eight traits with the strongest potential to be mapped using RS (plant growth and life forms, flammability properties, photosynthetic pathways and photosynthesis activity, plant height, leaf lifespan and phenology, specific leaf area, leaf nitrogen and phosphorous). The review indicated that imaging spectroscopy facilitates better retrievals of plant traits related to leaf biochemistry, photosynthesis and phenology rather than traits related to vegetations structure. Estimation of the canopy structure related traits (e.g. plant height) can certainly benefit from increasing synergies between imaging spectroscopy and active RS (radar or laser scanning). One of major challenges in RS of plant traits is to effectively suppress the negative influences of water absorption and canopy structure, which would facilitate more accurate retrievals of biochemical and photosynthesis-related traits. Secondly, a successful integration of RS and plant ecology concepts would require careful matching of spatial scales of in-situ trait data with RS observations.

    In Chapter 3, measurement methods and variability of total to projected leaf area within spruce crowns were investigated. Comparison of six laboratory methods revealed that methods using an elliptic approximation of a needle shape underestimated total leaf area compared to methods using a parallelepiped approximation. The variability in total to projected leaf area was primarily driven by the vertical sampling position and less by needle age or forest stand age. We found that total leaf area estimation has an important implication on RS of leaf chlorophyll content. An error associated with biased estimates of total leaf area can reach up to 30% of the expected chlorophyll range commonly found in forest canopies and therefore negatively influences the validation of RS-based chlorophyll maps. In Chapter 4, potentials of the continuum removal transformation for mapping of chlorophyll content in spruce canopies were investigated. We tested two methods based on continuum removal: artificial neural networks and an optical index. The optical index was newly designed here and it was based on the spectral continuum between 650 and 720 nm. Both continuum removal based methods exhibited superior accuracy in chlorophyll retrieval compared to commonly used narrow-band vegetation indices (e.g. NDVI, TCARI/OSAVI). The newly designed index was equally accurate, but certainly provided a more operational approach as compared to the neural network.

    In Chapter 5, mapping of ecosystem properties that underline ecosystem services provided by subalpine grasslands using RS methods was tested and further compared with a statistical plant trait-based modelling approach. Imaging spectroscopy in combination with empirical retrieval methods was partly successful to map ecosystem properties. The prediction accuracy at the calibration phase was comparable to the trait-based modelling approach. Spatial comparison between the two approaches revealed rather small agreement. The average fuzzy similarity between the approaches was around 20% for ecosystem properties, but in case of the total ecosystem service supply it decreased below 10%. However, the RS approach detected more variability in ecosystem properties and thereby in services, which was driven by local topography and microclimatic conditions, which could not be detected by the plant trait-based approach. Especially Chapters 2 and 5 indicated that one of the future RS research directions may be in spatial ecology, i.e. spatially explicit mapping of plant traits, ecosystem properties and ecosystem services. High quality RS data are certainly essential building elements for spatial ecology. But in order to address the effects of climate and land use changes on biodiversity and ecosystems, their properties and services, the integration of in-situ and RS data will be ultimately required. Therefore, more coherent experiments, where in-situ and RS data are measured simultaneously at different spatial scales, are needed in the future.

    Dietary heme induces acute oxidative stress, but delayed cytotoxicity and compensatory hyperproliferation in mouse colon
    IJssenagger, N. ; Rijnierse, A. ; Wit, N.J.W. de; Boekschoten, M.V. ; Dekker, J. ; Schonewille, A. ; Müller, M.R. ; Meer, M. van der - \ 2013
    Carcinogenesis 34 (2013)7. - ISSN 0143-3334 - p. 1628 - 1635.
    colorectal-cancer risk - red meat - rat colon - distal colon - ppar-alpha - consumption - chlorophyll - fish - carcinogenesis - proliferation
    Red meat consumption is associated with an increased colon cancer risk. Heme, present in red meat, injures the colon surface epithelium by generating cytotoxic and oxidative stress. Recently, we found that this surface injury is compensated by hyperproliferation and hyperplasia of crypt cells, which was induced by a changed surface to crypt signaling. It is unknown whether this changed signaling is caused by cytotoxic stress and/or oxidative stress, as these processes were never studied separately. The aim of this study was to determine the possible differential effects of dietary heme on these luminal stressors and their impact on the colonic mucosa after 2, 4, 7 and 14 days of heme feeding. Mice received a purified, humanized, control diet or the diet supplemented with 0.2 µmol heme/g. Oxidative and cytotoxic stress were measured in fecal water. Proliferation was determined by Ki67-immunohistochemistry and mucosal responses by whole-genome transcriptomics. After heme ingestion, there was an acute increase in reactive oxygen species (ROS) leading to increased levels of lipid peroxidation products. Mucosal gene expression showed an acute antioxidant response, but no change in cell turnover. After day 4, cytotoxicity of the colonic contents was increased and this coincided with differential signaling and hyperproliferation, indicating that cytotoxicity was the causal factor. Simultaneously, several oncogenes were activated, whereas the tumor suppressor p53 was inhibited. In conclusion, luminal cytotoxicity, but not ROS, caused differential surface to crypt signaling resulting in mucosal hyperproliferation and the differential expression of oncogenes and tumor suppressor genes.
    Trait estimation in herbaceous plant assemblages from in situ canopy spectra
    Roelofsen, H.D. ; Bodegom, P.M. van; Kooistra, L. ; Witte, J.M. - \ 2013
    Remote Sensing 5 (2013)12. - ISSN 2072-4292 - p. 6323 - 6345.
    least-squares regression - hyperspectral data - economics spectrum - vegetation indexes - indicator values - nitrogen-content - national-park - chlorophyll - reflectance - model
    Estimating plant traits in herbaceous plant assemblages from spectral reflectance data requires aggregation of small scale trait variations to a canopy mean value that is ecologically meaningful and corresponds to the trait content that affects the canopy spectral signal. We investigated estimation capacities of plant traits in a herbaceous setting and how different trait-aggregation methods influence estimation accuracies. Canopy reflectance of 40 herbaceous plant assemblages was measured in situ and biomass was analysed for N, P and C concentration, chlorophyll, lignin, phenol, tannin and specific water concentration, expressed on a mass basis (mg·g-1). Using Specific Leaf Area (SLA) and Leaf Area Index (LAI), traits were aggregated to two additional expressions: mass per leaf surface (mg·m-2) and mass per canopy surface (mg·m-2). All traits were related to reflectance using partial least squares regression. Accuracy of trait estimation varied between traits but was mainly influenced by the trait expression. Chlorophyll and traits expressed on canopy surface were least accurately estimated. Results are attributed to damping or enhancement of the trait signal upon conversion from mass based trait values to leaf and canopy surface expressions. A priori determination of the most appropriate trait expression is viable by considering plant growing strategies
    Low temperature-induced lycopene degradaton in red ripe tomato evaluated by remittance spectroscopy
    Farneti, B. ; Schouten, R.E. ; Woltering, E.J. - \ 2012
    Postharvest Biology and Technology 73 (2012). - ISSN 0925-5214 - p. 22 - 27.
    solanum-lycopersicon l. - chilling-injury - pericarp discs - heat-shocks - apple fruit - ion leakage - carotenoids - chlorophyll - cultivars - maturity
    Tomatoes are mostly harvested at the orange and red-ripe stages. A survey among consumers indicated that tomatoes are most often stored in the refrigerator well below 10 °C, a temperature considered harmful for chilling sensitive products such as tomato. Also during distribution, tomatoes may be exposed to chilling temperatures. The effects of storage at chilling temperatures on quality aspects of tomatoes were investigated. The colour and lycopene content of red ripe tomatoes of two cultivars (cocktail and round type) was evaluated during 20 days of storage at 4, 8, 12 and 16 °C. Colour was repeatedly measured over time by tristimulus colour measurements, RGB image analysis and colour intensity was scored by eye using a consumer panel. Lycopene content was repeatedly assessed by following the NAI index over time. This index, obtained from remittance VIS spectroscopy, was found to relate closely to the lycopene level as measured by HPLC measurements of pericarp tissue. Temperatures below 12 °C resulted in lycopene loss in ripe-red tomatoes and substantial colour loss well assessed by visual evaluation. Colour measurement using tristimulus colour measurements and RGB image analysis did not correlate well with lycopene content. Prior hot water treatment did not prevent lycopene loss. Results show that storage of red ripe tomatoes at chilling temperatures reduces the nutritional and presumed health promoting value and affects fruit visual quality.
    Is there a decline in marine phytoplankton?
    McQuatters-Gollop, A. ; Reid, P.C. ; Edwards, M. ; Burkill, P.H. ; Castellani, C. ; Batten, S. ; Gieskes, W. ; Beare, D.J. ; Bidigare, R.R. ; Head, E. ; Johnson, R. ; Kahru, M. ; Koslow, J.A. ; Pena, A. - \ 2011
    Nature 472 (2011)7342. - ISSN 0028-0836 - p. E6 - E7.
    long-term - northeast atlantic - ocean - chlorophyll - plankton - biomass - variability - trends - sea
    Leaf area index estimation with MODIS reflectance time series and model inversion during full rotations of Eucalyptus plantations
    Maire, G. Le; Marsden, C. ; Verhoef, W. ; Ponzoni, F.J. ; Seen, D. Lo; Bégué, A. ; Stape, J.L. ; Nouvellon, Y. - \ 2011
    Remote Sensing of Environment 115 (2011)2. - ISSN 0034-4257 - p. 586 - 599.
    optical-properties - vegetation index - bidirectional reflectance - use efficiency - canopy - imagery - forest - chlorophyll - resolution - globulus
    The leaf area index (LAI) of fast-growing Eucalyptus plantations is highly dynamic both seasonally and inter-annually, and is spatially variable depending on pedo-climatic conditions. LAI is very important in determining the carbon and water balance of a stand, but is difficult to measure during a complete stand rotation and at large scales. Remote-sensing methods allowing the retrieval of LAI time series with accuracy and precision are therefore necessary. Here, we tested two methods for LAI estimation from MODIS 250m resolution red and near-infrared (NIR) reflectance time series. The first method involved the inversion of a coupled model of leaf reflectance and transmittance (PROSPECT4), soil reflectance (SOILSPECT) and canopy radiative transfer (4SAIL2). Model parameters other than the LAI were either fixed to measured constant values, or allowed to vary seasonally and/or with stand age according to trends observed in field measurements. The LAI was assumed to vary throughout the rotation following a series of alternately increasing and decreasing sigmoid curves. The parameters of each sigmoid curve that allowed the best fit of simulated canopy reflectance to MODIS red and NIR reflectance data were obtained by minimization techniques. The second method was based on a linear relationship between the LAI and values of the GEneralized Soil Adjusted Vegetation Index (GESAVI), which was calibrated using destructive LAI measurements made at two seasons, on Eucalyptus stands of different ages and productivity levels. The ability of each approach to reproduce field-measured LAI values was assessed, and uncertainty on results and parameter sensitivities were examined. Both methods offered a good fit between measured and estimated LAI (R2 = 0.80 and R2 = 0.62 for model inversion and GESAVI-based methods, respectively), but the GESAVI-based method overestimated the LAI at young ages.
    Estimating specific inherent optical properties of tropical coastal waters using bio-optical model inversion and in situ measurements: case of the Berau estuary, East Kalimantan, Indonesia
    Ambarwulan, W. ; Salama, M.S. ; Mannaerts, C.M. ; Verhoef, W. - \ 2011
    Hydrobiologia 658 (2011)1. - ISSN 0018-8158 - p. 197 - 211.
    dissolved organic-matter - ocean color - scattering coefficients - absorption - chlorophyll - phytoplankton - seawifs - reflectance - throughflow - variability
    Specific inherent optical properties (SIOP) of the Berau coastal waters were derived from in situ measurements and inversion of an ocean color model. Field measurements of water-leaving reflectance, total suspended matter (TSM), and chlorophyll a (Chl a) concentrations were carried out during the 2007 dry season. The highest values for SIOP were found in the turbid waters, decreasing in value when moving toward offshore waters. The specific backscattering coefficient of TSM varied by an order of magnitude and ranged from 0.003 m2 g-1, for clear open ocean waters, to 0.020 m2 g-1, for turbid waters. On the other hand, the specific absorption coefficient of Chl a was relatively constant over the whole study area and ranged from 0.022 m2 mg-1, for the turbid shallow estuary waters, to 0.027 m2 mg-1, for deeper shelf edge ocean waters. The spectral slope of colored dissolved organic matter light absorption was also derived with values ranging from 0.015 to 0.011 nm-1. These original derived values of SIOP in the Berau estuary form a corner stone for future estimation of TSM and Chl a concentration from remote sensing data in tropical equatorial waters
    Chlorophyll Fluorescence of seeds A non-destructive marker foor seed maturity and seed quality
    Jalink, H. - \ 2010
    fluorescentie - chlorofyl - zaden - methodologie - kwaliteitszorg - rijpheid - fluorescence - chlorophyll - seeds - methodology - quality management - maturity
    A method has been developed for the assessment of maturity and quality of seeds. The method is based on a non-destructive measurement of chlorop¬hyll-a in individual seeds.
    Beoordeling van Zaadkwaliteit met behulp van Chlorofyl Fluorescentie Beelden
    Jalink, H. - \ 2010
    zaadkieming - chlorofyl - embryo's - fluorescentie - zaden - technieken - capsicum - glastuinbouw - seed germination - chlorophyll - embryos - fluorescence - seeds - techniques - capsicum - greenhouse horticulture
    Tijdens het kiemingsproces van zaden wordt o.a. chlorofyl gevormd. Dit chlorofyl wordt aangemaakt door het embryo. Het is gebleken dat de toename van chlorofyl een maat is voor het verloop van het kiemingsproces. Dit chlorofyl kan gevoelig worden gemeten met een fluorescentietechniek.
    Monitoring photosynthesis in individual cells of Synechocytis sp. PCC 6803 on a picosecond timescale
    Krumova, S.K.B. ; Laptenok, S. ; Borst, J.W. ; Ughy, B. ; Gombos, Z. ; Aijani, G. ; Amerongen, H. van - \ 2010
    Biophysical Journal 99 (2010)6. - ISSN 0006-3495 - p. 2006 - 2015.
    fluorescence emission-spectra - excitation-energy transfer - intact photosystem-ii - thylakoid membrane - synechococcus 6301 - phycobilisome - kinetics - time - spectroscopy - chlorophyll
    Picosecond fluorescence kinetics of wild-type (WT) and mutant cells of Synechocystis sp. PCC 6803, were studied at the ensemble level with a streak-camera and at the cell level using fluorescence-lifetime-imaging microscopy (FLIM). The FLIM measurements are in good agreement with the ensemble measurements, but they (can) unveil variations between and within cells. The BE mutant cells, devoid of photosystem II (PSII) and of the light-harvesting phycobilisomes, allowed the study of photosystem I (PSI) in vivo for the first time, and the observed 6-ps equilibration process and 25-ps trapping process are the same as found previously for isolated PSI. No major differences are detected between different cells. The PAL mutant cells, devoid of phycobilisomes, show four lifetimes: 20 ps (PSI and PSII), 80 ps, 440 ps, and 2.8 ns (all due to PSII), but not all cells are identical and variations in the kinetics are traced back to differences in the PSI/PSII ratio. Finally, FLIM measurements on WT cells reveal that in some cells or parts of cells, phycobilisomes are disconnected from PSI/PSII. It is argued that the FLIM setup used can become instrumental in unraveling photosynthetic regulation mechanisms in the future
    The Selectivity of Milking of Dunaliella salina
    Kleinegris, D.M.M. ; Janssen, M.G.J. ; Brandenburg, W.A. ; Wijffels, R.H. - \ 2010
    Marine Biotechnology 12 (2010)1. - ISSN 1436-2228 - p. 14 - 23.
    beta-carotene production - 2-phase bioreactors - low-temperature - photosystem-ii - green-algae - accumulation - bardawil - chlorophyll - extraction - protein
    The process of the simultaneous production and extraction of carotenoids, milking, of Dunaliella salina was studied. We would like to know the selectivity of this process. Could all the carotenoids produced be extracted? And would it be possible to vary the profile of the produced carotenoids and, consequently, influence the type of carotenoids extracted? By using three different D. salina strains and three different stress conditions, we varied the profiles of the carotenoids produced. Between Dunaliella bardawil and D. salina 19/18, no remarkable differences were seen in the extraction profiles, although D. salina 19/18 seemed to be better extractable. D. salina 19/25 was not “milkable” at all. The milking process could only be called selective for secondary carotenoids in case gentle mixing was used. In aerated flat-panel photobioreactors, extraction was much better, but selectiveness decreased and also chlorophyll and primary carotenoids were extracted. This was possibly related to cell damage due to shear stress
    Probabilistic modelling of exposure doses and implications for health risk characterization: Glycoalkaloids from potatoes
    Ruprich, J. ; Rehurkova, I. ; Boon, P.E. ; Svensson, K. ; Moussavian, S. ; Voet, H. van der; Bosgra, S. ; Klaveren, J.D. van; Busk, L. - \ 2009
    Food and Chemical Toxicology 47 (2009)12. - ISSN 0278-6915 - p. 2899 - 2905.
    tubers solanum-tuberosum - steroidal glycoalkaloids - temperature - chlorophyll - cultivars - storage - light - humans - foods - l.
    Potatoes are a source of glycoalkaloids (GAs) represented primarily by a-solanine and a-chaconine (about 95%). Content of GAs in tubers is usually 10–100 mg/kg and maximum levels do not exceed 200 mg/kg. GAs can be hazardous for human health. Poisoning involve gastrointestinal ailments and neurological symptoms. A single intake of >1–3 mg/kg b.w. is considered a critical effect dose (CED). Probabilistic modelling of acute and chronic (usual) exposure to GAs was performed in the Czech Republic, Sweden and The Netherlands. National databases on individual consumption of foods, data on concentration of GAs in tubers (439 Czech and Swedish results) and processing factors were used for modelling. Results concluded that potatoes currently available at the European market may lead to acute intakes >1 mg GAs/kg b.w./day for upper tail of the intake distribution (0.01% of population) in all three countries. 50 mg GAs/kg raw unpeeled tubers ensures that at least 99.99% of the population does not exceed the CED. Estimated chronic (usual) intake in participating countries was 0.25, 0.29 and 0.56 mg/kg b.w./day (97.5% upper confidence limit). It remains unclear if the incidence of GAs poisoning is underreported or if assumptions are the worst case for extremely sensitive persons
    Sink stimulation of leaf photosynthesis by the carbon costs of rhizobial and arbuscular mycorrhizal fungal symbioses
    Kaschuk, G. - \ 2009
    Wageningen University. Promotor(en): Ken Giller; Thomas Kuijper, co-promotor(en): Peter Leffelaar; M. Hungria. - [S.l. : S.n. - ISBN 9789085853923 - 160
    fotosynthese - mycorrhizae - source-sink relaties - chlorofyl - fluorescentie - gebruiksefficiëntie - plantenvoeding - photosynthesis - mycorrhizas - source sink relations - chlorophyll - fluorescence - use efficiency - plant nutrition

    Key words: biochemical model of leaf photosynthesis; carbon sink strength; chlorophyll fluorescence; harvest index; leaf protein; leaf senescence; legumes; photosynthetic nutrient use efficiency; Pi recycling; source-sink regulation; ureides

    One of the most fascinating processes in plant physiology and agronomy is the capability of legumes to associate symbiotically with rhizobial bacteria and arbuscular mycorrhizal (AM) fungi. The legumes supply photosynthates in exchange for nitrogen, derived from biological N2 fixation, and soil nutrients mainly phosphate, obtained from foraging of AM fungi from the soil. The rhizobial and arbuscular mycorrhizal symbioses each may use 4-16% of recently fixed photosynthates to maintain their activity, growth and reserves, but in turn, may supply 100% of the plant nutrient requirements. The C costs of the symbioses are often assumed to limit plant productivity due to photosynthate competition between the microsymbiont and the host. In addition, the C costs are often used as an entry point to understand the evolution of the symbioses.
    It is intriguing that despite of the symbiotic C costs, plants associated with rhizobia and/or AM fungi often produce more biomass and grains than fertilized plants. Increases in plant growth are traditionally attributed to improved plant nutrition and enhanced photosynthesis. This thesis gives evidence that plants – and particularly legumes – are able to overcome any putative C limitation associated with rhizobial and AM fungal symbioses by increasing the rates of photosynthesis due to sink stimulation, over and above the expected nutritional benefits from the symbioses. Sink stimulation of photosynthesis is a consequence of increased C demand from photosynthesis, which increases the export of triose-P from chloroplasts, recycling more inorganic phosphates and activating more photosynthetic enzymes. In the thesis, I report a literature study, which provides a framework for the quantification of sink stimulation of photosynthesis. Apparently, sink stimulation of photosynthesis by symbioses just equals the C costs, which in the long term is still beneficial for plant growth. Sink stimulation of photosynthesis implies that plants and symbioses are not limited by photosynthates, which means that the cost : benefit theories for symbioses need to be re-conceptualized.
    Photosynthesis is limited by three biochemical processes: rubisco activity, electron transport, and triose-P export (often referred as sink limitation). In Chapter 3, I apply a biochemical model expressing these three limitations in CO2 response curves of soybean (Glycine max [L.] Merrill) inoculated with rhizobial strains with putative different C costs (Bradyrhizobium japonicum CPAC 390 or CPAC 7) or fertilized with KNO3, to understand the effects of rhizobial symbioses on the photosynthetic capacity. Plants associated with putatively more expensive strains have higher photosynthetic capacity than those associated with less ‘expensive strains’. The effect of sink stimulation of photosynthesis is evident because plants with higher triose-P export rates consistently had higher rates of electron transport and rubisco activity. These results suggest that the C costs of rhizobial symbioses generate feedbacks between the rates of triose-P export with rubisco activity and electron transport rates.
    I also describe three subsequent experiments with two different soybean varieties nodulated with two rhizobial strains or fertilized with two doses of KNO3 fertilizer. Plants associated with rhizobial symbioses always had higher rates of photosynthesis and accumulated less starch in the leaves than N-fertilized plants throughout the whole cycle. Furthermore, nodulated plants maintained higher chlorophyll concentrations for a longer period than N-fertilized plants. Both photosynthesis and N2 fixation were synchronized over the plant cycle. One of the conclusions of Chapter 4 is that C costs of rhizobial symbioses lead to sink stimulation of photosynthesis, which in turn, delays leaf senescence. These mechanisms together are likely to contribute for increase in plant productivity.
    Overall, the thesis indicates that the C costs of symbioses are not disadvantageous, as usually thought. Higher activity of rhizobial and AM fungal symbioses results in sink stimulation of photosynthesis, which leads to higher plant growth over time. Sink stimulation of photosynthesis implies that the microsymbionts and plants are not limited by photosynthate. Increased rates of photosynthesis in initial stages of plant development delay the rates of leaf senescence in the later stages of plant development. The C costs of symbioses bring advantages to the plant’s adaptation under elevated CO2 concentration, because they remove the sink limitation of photosynthesis. It means that effectiveness of the symbioses (the capacity to supply nutrients) is more important than the C costs or the efficiency with which photosynthates are used.

    Visiontechnieken brengen zichtbare en onzichtbar kenmerken in beeld
    Pekkeriet, E.J. - \ 2008
    Onder Glas 5 (2008)12. - p. 5 - 7.
    tuinbouwbedrijven - sierplanten - machine vision - computertechnieken - videocamera's - chlorofyl - gewaskwaliteit - infraroodspectrofotometrie - röntgenstraling - glastuinbouw - groenten - potplanten - market gardens - ornamental plants - machine vision - computer techniques - video cameras - chlorophyll - crop quality - infrared spectrophotometry - x radiation - greenhouse horticulture - vegetables - pot plants
    Binnen de glastuinbouw wordt de 2D-visiontechniek al volop toegepast bij het sorteren en het bepalen van de kwaliteit. Nieuw is het aansturen van een robotarm. Nog nieuwer zijn de verschillende 3-D-technieken, zoals lasertriangulatie, stereovisie, 'volumetric intersection' en visiontechnieken die buiten het zichtbare spectrum werken
    Modelling spatial heterogeneity of phytoplankton in Lake Mangueira, a large shallow subtropical lake in South Brazil
    Fragoso, C.R. ; Motta Marques, D.M.L. ; Collischonn, W. ; Tucci, C.E.M. ; Nes, E.H. van - \ 2008
    Ecological Modelling 219 (2008)1-2. - ISSN 0304-3800 - p. 125 - 137.
    water-quality - salinity simulations - growth - temperature - stability - dynamics - scale - sea - coefficients - chlorophyll
    We present a model describing phytoplankton growth in Lake Mangueira, a large subtropical lake in the Taim Hydrological System in South Brazil (817 km2, average depth 2 m). The horizontal 2D model consists of three modules: (a) a detailed hydrodynamic module for shallow water, which deals with wind-driven quantitative flows and water level, (b) a nutrient module, which deals with nutrient transport mechanisms and some conversion processes and (c) a biological module, which describes phytoplankton growth in a simple way. We solved the partial differential equations numerically by applying an efficient semi-implicit finite differences method to a regular grid. Hydrodynamic parameters were calibrated to continuous measurements of the water level at two different locations of the lake. An independent validation data set showed a good fit of the hydrodynamic module (R2 ¿ 0.92). The nutrient and biological modules were parameterized using literature data and verified by comparing simulated phytoplankton patterns with remote sensing data from satellite images and field data of chlorophyll a. Moreover, a sensitivity analyses showed which parameters had the largest influence on the simulated phytoplankton biomass. The model could identify zones with a higher potential for eutrophication. It has shown to be a first step towards a management tool for prediction of the trophic state in subtropical lakes, estuaries and reservoirs.
    Optimalisatie van de stikstofbemesting van Engels raaigras
    Schoot, J.R. van der - \ 2007 2007 (2007)15 jan.
    akkerbouw - stikstofmeststoffen - lolium perenne - zaadproductie - chlorofyl - bemesting - rassen (planten) - cultivars - mestgiften - stikstof - arable farming - nitrogen fertilizers - lolium perenne - seed production - chlorophyll - fertilizer application - varieties - cultivars - dressings - nitrogen
    In het stikstofadvies voor Engels raaigras, zoals vastgesteld in onderzoek van PA(G)V in de periode 1978-1984, wordt geen onderscheid gemaakt naar typen en rassen en wordt aanbevolen de benodigde hoeveelheid stikstof éénmalig in het vroege voorjaar te verstrekken. Gezien de grote verschillen in gewasstructuur en ontwikkelingssnelheid die er bij de verschillende typen en rassen van Engels raaigras bestaan, kan het stikstofadvies vermoedelijk worden verfijnd. Deling van de stikstofgift kan, al of niet met behulp van de chlorofylmeter, daarnaast ook zorgen voor lagere oogstrisico's of betere opbrengsten. In opdracht van het Productschap Granen, Zaden en Peulvruchten is daarom onderzoek uitgevoerd naar typen en rassen bij verschillende bemestingsniveau's, de gebruiksmogelijkheden van de chlorofylmeter en de effecten van deling van stikstof.
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