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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    Morphological and physiological responses of the potato stem transport tissues to dehydration stress
    Aliche, Ernest B. ; Prusova-Bourke, Alena ; Ruiz-Sanchez, Mariam ; Oortwijn, Marian ; Gerkema, Edo ; As, Henk Van; Visser, Richard G.F. ; Linden, C.G. van der - \ 2020
    Planta 251 (2020)2. - ISSN 0032-0935
    Drought - MRI - Phloem - Potato - Sugar transport - Xylem

    Main conclusion: Adaptation of the xylem under dehydration to smaller sized vessels and the increase in xylem density per stem area facilitate water transport during water-limiting conditions, and this has implications for assimilate transport during drought. Abstract: The potato stem is the communication and transport channel between the assimilate-exporting source leaves and the terminal sink tissues of the plant. During environmental stress conditions like water scarcity, which adversely affect the performance (canopy growth and tuber yield) of the potato plant, the response of stem tissues is essential, however, still understudied. In this study, we investigated the response of the stem tissues of cultivated potato grown in the greenhouse to dehydration using a multidisciplinary approach including physiological, biochemical, morphological, microscopic, and magnetic resonance imaging techniques. We observed the most significant effects of water limitation in the lower stem regions of plants. The light microscopy analysis of the potato stem sections revealed that plants exposed to this particular dehydration stress have higher total xylem density per unit area than control plants. This increase in the total xylem density was accompanied by an increase in the number of narrow-diameter xylem vessels and a decrease in the number of large-diameter xylem vessels. Our MRI approach revealed a diurnal rhythm of xylem flux between day and night, with a reduction in xylem flux that is linked to dehydration sensitivity. We also observed that sink strength was the main driver of assimilate transport through the stem in our data set. These findings may present potential breeding targets for drought tolerance in potato.

    Magnetic resonance imaging suggests functional role of previous year vessels and fibres in ring-porous sap flow resumption
    Copini, Paul ; Vergeldt, Frank J. ; Fonti, Patrick ; Sass-Klaassen, Ute ; Ouden, Jan Den; Sterck, Frank ; Decuyper, Mathieu ; Gerkema, Edo ; Windt, Carel W. ; As, Henk Van - \ 2019
    Tree Physiology 39 (2019). - ISSN 0829-318X - p. 1009 - 1018.
    Reactivation of axial water flow in ring-porous species is a complex process related to stem water content and developmental stage of both earlywood-vessel and leaf formation. Yet empirical evidence with non-destructive methods on the dynamics of water flow resumption in relation to these mechanisms is lacking. Here we combined in vivo magnetic resonance imaging and wood-anatomical observations to monitor the dynamic changes in stem water content and flow during spring reactivation in 4-year-old pedunculate oaks (Quercus robur L.) saplings. We found that previous year latewood vessels and current year developing earlywood vessels form a functional unit for water flow during growth resumption. During spring reactivation, water flow shifted from latewood towards the new earlywood, paralleling the formation of earlywood vessels and leaves. At leaves' full expansion, volumetric water content of previous rings drastically decreased due to the near-absence of water in fibre tissue. We conclude (i) that in ring-porous oak, latewood vessels play an important hydraulic role for bridging the transition between old and new water-conducting vessels and (ii) that fibre and parenchyma provides a place for water storage.
    Iron, cobalt, and gadolinium transport in methanogenic granules measured by 3D magnetic resonance imaging
    Bartacek, Jan ; Vergeldt, Frank J. ; Maca, Josef ; Gerkema, Edo ; As, Henk Van ; Lens, Piet N.L. - \ 2016
    Frontiers in Environmental Science 4 (2016)MAR. - ISSN 2296-665X
    Granular biofilm - Magnetic resonance microscopy - Metal diffusion - Metal transport - Methanogenic granular sludge

    Description of processes such as bioaccumulation, bioavailability and biosorption of heavy metals in biofilm matrixes requires the quantification of their transport. This study shows 3D MRI measurements of the penetration of free (Fe 2+ , Co 2+ and Gd 3+ ) and complexed ([FeEDTA] 2- and [GdDTPA] 2- ) metal ions in a single methanogenic granule. Interactions (sorption or precipitation) between free metals and the biofilm matrix result in extreme shortening of the spin-spin relaxation time (T 2 ) and a decrease of the amplitude (A 0 ) of the MRI signal, which hampers the quantification of the metal concentration inside the granular sludge matrix. MRI images clearly showed the presence of distinct regions (dead or living biomass, cracks, and precipitates) in the granular matrix, which influenced the metal transport. For the free metal ions, a reactive barrier was formed that moved through the granule, especially in the case of Gd 2+ . Chelated metals penetrated faster and without reaction front. Diffusion of [GdDTPA] 2- could be quantified, revealing the course of its transport and the uneven (0.2-0.4 mmolL -1 ) distribution of the final [GdDTPA] 2- concentration within the granular biofilm matrix at equilibrium.

    Rhizophoraceae Mangrove Saplings Use Hypocotyl and Leaf Water Storage Capacity to Cope with Soil Water Salinity Changes
    Lechthaler, Silvia ; Robert, Elisabeth M.R. ; Tonné, Nathalie ; Prusova, Alena ; Gerkema, Edo ; As, Henk Van; Koedam, Nico ; Windt, Carel W. - \ 2016
    Frontiers in Plant Science 7 (2016)June2016. - ISSN 1664-462X
    Some of the most striking features of Rhizophoraceae mangrove saplings are their voluminous cylinder-shaped hypocotyls and thickened leaves. The hypocotyls are known to serve as floats during seed dispersal (hydrochory) and store nutrients that allow the seedling to root and settle. In this study we investigate to what degree the hypocotyls and leaves can serve as water reservoirs once seedlings have settled, helping the plant to buffer the rapid water potential changes that are typical for the mangrove environment. We exposed saplings of two Rhizophoraceae species to three levels of salinity (15, 30, and 0–5‰, in that sequence) while non-invasively monitoring changes in hypocotyl and leaf water content by means of mobile NMR sensors. As a proxy for water content, changes in hypocotyl diameter and leaf thickness were monitored by means of dendrometers. Hypocotyl diameter variations were also monitored in the field on a Rhizophora species. The saplings were able to buffer rapid rhizosphere salinity changes using water stored in hypocotyls and leaves, but the largest water storage capacity was found in the leaves. We conclude that in Rhizophora and Bruguiera the hypocotyl offers the bulk of water buffering capacity during the dispersal phase and directly after settlement when only few leaves are present. As saplings develop more leaves, the significance of the leaves as a water storage organ becomes larger than that of the hypocotyl.
    Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots
    Peuke, A.D. ; Gessler, A. ; Trumbore, S. ; Windt, C.W. ; Homan, N. ; Gerkema, E. ; As, H. van - \ 2015
    Plant, Cell & Environment 38 (2015)3. - ISSN 0140-7791 - p. 433 - 447.
    carbon-isotope composition - mushrooms agaricus-bisporus - distance water transport - organic-matter - membrane-permeability - assimilate transport - plants - leaves - starch - stress
    Anoxic conditions should hamper the transport of sugar in the phloem, as this is an active process. The canopy is a carbohydrate source and the roots are carbohydrate sinks.By fumigating the shoot with N2 or flooding the rhizosphere, anoxic conditions in the source or sink, respectively, were induced. Volume flow, velocity, conducting area and stationary water of the phloem were assessed by non-invasive magnetic resonance imaging (MRI) flowmetry. Carbohydrates and d13C in leaves, roots and phloem saps were determined. Following flooding, volume flow and conducting area of the phloem declined and sugar concentrations in leaves and in phloem saps slightly increased. Oligosaccharides appeared in phloem saps and after 3 d, carbon transport was reduced to 77%. Additionally, the xylem flow declined and showed finally no daily rhythm. Anoxia of the shoot resulted within minutes in a reduction of volume flow, conductive area and sucrose in the phloem sap decreased. Sugar transport dropped to below 40% by the end of the N2 treatment. However, volume flow and phloem sap sugar tended to recover during the N2 treatment. Both anoxia treatments hampered sugar transport. The flow velocity remained about constant, although phloem sap sugar concentration changed during treatments. Apparently, stored starch was remobilized under anoxia.
    Visualization of the stem water content of two genera with secondary phloem produced by successive cambia through Magnetic Resonance Imaging (MRI)
    Robert, E.M.R. ; Schmitz, N. ; Copini, P. ; Gerkema, E. ; Vergeldt, F.J. ; Windt, C.W. ; Beeckman, H. ; Koedam, N. ; As, H. van - \ 2014
    The Journal of Plant Hydraulics 1 (2014). - ISSN 2268-4565 - 8 p.
    Shrubs and trees with secondary phloem tissue produced by successive cambia mainly occur in habitats characterized by a periodical or continuous lack of water availability. The amount of this secondary phloem tissue in stems of Avicennia trees rises with increasing soil water salinity and decreasing inundation frequency. Hence, increased water storage in secondary phloem tissue produced by successive cambia was put forward to be advantageous in harsh environmental conditions. It was however never tested whether the secondary phloem cells over the entire stem of woody species showing this wood anatomical feature are indeed water-filled as expected. In this preliminary and pioneering study, we use magnetic resonance imaging (MRI) to visualize the stem water content of three species with successive cambia, the mangroves Avicennia marina and A. officinalis and the non-mangrove Bougainvillea spectabilis. Measurements were conducted in living plants. We tested the hypothesis that not only the outermost phloem tissue has high water content but also the secondary phloem tissues over the entire stem from the bark inward to the pith, herewith serving as water storage sites. We can conclude that all secondary phloem tissue of both Bougainvillea and Avicennia has high water contents. This aligns with the contribution of secondary phloem tissue produced by successive cambia to ecological success in conditions of physiological drought. Further study should however be done to understand the mechanisms through which this secondary phloem tissue contributes to the water household of plants in conditions of water shortage.
    Anomalies in moisture transport during broccoli drying monitored by MRI?
    Jin, X. ; Boxtel, A.J.B. van; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Straten, G. van; Boom, R.M. ; Sman, R.G.M. van der - \ 2012
    Faraday Discussions 158 (2012). - ISSN 1359-6640 - p. 65 - 75.
    viscoelastic behavior - cooking - model - nmr - simulation - carrot - grain - food - meat
    Magnetic resonance imaging (MRI) offers unique opportunities to monitor moisture transport during drying or heating of food, which can render unexpected insights. Here, we report about MRI observations made during the drying of broccoli stalks indicating anomalous drying behaviour. In fresh broccoli samples the moisture content in the core of the sample increases during drying, which conflicts with Fickian diffusion. We have put the hypothesis that this increase of moisture is due to the stress diffusion induced by the elastic impermeable skin. Pre-treatments that change skin and bulk elastic properties of broccoli show that our hypothesis of stress-diffusion is plausible.
    The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge
    Bartacek, J. ; Fermoso, F.G. ; Vergeldt, F. ; Gerkema, E. ; Maca, J. ; As, H. van; Lens, P.N.L. - \ 2012
    Water Science and Technology 65 (2012)10. - ISSN 0273-1223 - p. 1875 - 1881.
    afvalwaterbehandeling - bioreactoren - anaërobe omstandigheden - korrelslib - biologische beschikbaarheid - metalen - toxiciteit - kernspintomografie - waste water treatment - bioreactors - anaerobic conditions - granular sludge - bioavailability - metals - toxicity - magnetic resonance imaging - magnetic-resonance - dynamics - immobilization - biofilm - nickel
    Bioavailability of metals in anaerobic granular sludge has been extensively studied, because it can have a major effect on metal limitation and metal toxicity to microorganisms present in the sludge. Bioavailability of metals can be manipulated by bonding to complexing molecules such as ethylenediaminetetraacetate (EDTA) or diethylenetriaminepentaacetate (DTPA). It has been shown that although the stimulating effect of the complexed metal species (e.g. [CoEDTA]2-) is very fast, it is not sustainable when applied to metal-limited continuously operated reactors. The present paper describes transport phenomena taking place inside single methanogenic granules when the granules are exposed to various metal species. This was done using magnetic resonance imaging (MRI). The MRI results were subsequently related to technological observations such as changes in methanogenic activity upon cobalt injection into cobalt-limited up-flow anaerobic sludge blanket (UASB) reactors. It was shown that transport of complexed metal species is fast (minutes to tens of minutes) and complexed metal can therefore quickly reach the entire volume of the granule. Free metal species tend to interact with the granular matrix resulting in slower transport (tens of minutes to hours) but higher final metal concentrations.
    Moisture distribution in broccoli: measurements by MRI hot air drying experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2011
    Procedia Food Science 1 (2011). - ISSN 2211-601X - p. 640 - 646.
    profiles - nmr - diffusivity - model - food - gel
    The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content.
    Moisture Distribution in Broccoli: Measurements by MRI Hot Air Drying Experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2011
    ABSTRACT The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content. Keywords: diffusion properties; MRI; convective drying; moisture profiles
    Investigation on the influence of pre-treatments on drying behaviour of broccoli by MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Straten, G. van; Boom, R.M. ; Boxtel, A.J.B. van - \ 2011
    Abstract: Magnetic Resonance Imaging (MRI) allows the monitoring of internal moisture content of food products during drying non-destructively. In an experimental set-up with continuous and controlled hot air supply, the internal moisture distribution of broccoli with different pre-treatments are measured during drying. Moisture distribution, drying rate and shrinkage are compared and analyzed quantitatively. MRI results indicated that for fresh broccoli stalks the moisture content in the core of the sample increased after some hours of drying. With pre-treatments as peeling, blanching or freezing the moisture transport barrier in the skin of the broccoli sample was reduced. Shrinkage was uniform for most of the pre-treated samples and the moisture increment in the core did not occur. It was also found that with these pre-treatments progress of drying enhanced significantly. Therefore, from an drying efficiency and economic point of view, pre-treatments prior to drying offer important opportunities. Keywords: MRI, hot air drying, broccoli stalk, increased moisture content, pre-treatments
    Characterization of water diffusion in food products for MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2010
    Characterization of water diffusion in food products from MRI experiments
    Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; As, H. van; Boxtel, A.J.B. van - \ 2010
    MRI in soils: determination of water concent changes due to root water uptake by means of a multi-slice-multi-echo sequence (MSME)
    Pohlmeier, A. ; Vergeldt, F. ; Gerkema, E. ; As, H. van; Dusschoten, D. van; Vereecken, H. - \ 2010
    The Open Magnetic Resonance Journal 3 (2010). - ISSN 1874-7698 - p. 69 - 74.
    Root water uptake by ricinus communis (castor bean) in fine sand was investigated using MRI with multiecho sampling. Before starting the experiments the plants germinated and grew for 3 weeks in a cylindrical container with a diameter of 9 cm. Immediately before the MRI experiments started, the containers were water-saturated and sealed, so water content changes were only caused by root water uptake. In continuation of a preceding work, where we applied SPRITE we tested a multi-echo multi-slice sequence (MSME). In this approach, the water content was imaged by setting TE = 6.76 ms and nE = 128 with an isotropic resolution of 3.1mm. We calculated the water content maps by biexponential fitting of the multi-slice echo train data and normalisation on reference cuvettes filled with glass beads and 1 mM NiCl2 solution. The water content determination was validated by comparing to mean gravimetric water content measurements. By coregistration with the root architecture, visualised by a 3D fast spin echo sequence (RARE), we conclude that the largest water content changes occurred in the neighbourhood of the roots and in the upper layers of the soil.
    1H-NMR study of the impact of high pressure and thermal processing on cell membrane integrity of onions
    Gonzalez, M.E. ; Barrett, D.M. ; McCarthy, M.J. ; Vergeldt, F.J. ; Gerkema, E. ; Matser, A.M. ; As, H. van - \ 2010
    Journal of Food Science 75 (2010)7. - ISSN 0022-1147 - p. E417 - E425.
    spin-spin relaxation - mushrooms agaricus-bisporus - nuclear-magnetic-resonance - water diffusion - lactobacillus-plantarum - vacuolar symplast - osmotic-stress - maize roots - pfg-nmr - tissue
    Proton nuclear magnetic resonance (1H-NMR) relaxometry was used to study the effects of high pressure and thermal processing on membrane permeability and cell compartmentalization, important components of plant tissue texture. High pressure treated onions were subjected to pressure levels from 20 to 200 MPa at 5 min hold time at initial temperatures of 5 and 20 °C. Thermally treated onions were exposed for 30 min at temperatures from 40 to 90 °C. Loss of membrane integrity was clearly shown by changes in transverse relaxation time (T2) of water at temperatures of 60 °C and above. Destabilization effects on membranes exposed to high pressure were observed at 200 MPa as indicated by T2 measurements and cryo-scanning electron microscopy (Cryo-SEM). T2 relaxation successfully discriminated different degrees of membrane damage based on the T2 shift of the vacuolar component. Analyses of the average water self-diffusion coefficient indicated less restricted diffusion after membrane rupture occurred in cases of severe thermal treatments. Milder processing treatments yielded lower average diffusion coefficients than the controls. 1H-NMR proved to be an effective method for quantification of cell membrane damage in onions and allowed for the comparison of different food processes based on their impact on tissue integrity
    Quantitative permeability imaging of plant tissues
    Sibgatullin, T. ; Vergeldt, F.J. ; Gerkema, E. ; As, H. van - \ 2010
    European Biophysics Journal 39 (2010)4. - ISSN 0175-7571 - p. 699 - 710.
    pulsed-field gradient - time-dependent diffusion - nuclear-magnetic-resonance - water self-diffusion - membrane-permeability - pfg nmr - osmotic-stress - porous-media - yeast-cells - echo nmr
    A method for mapping tissue permeability based on time-dependent diffusion measurements is presented. A pulsed field gradient sequence to measure the diffusion encoding time dependence of the diffusion coefficients based on the detection of stimulated spin echoes to enable long diffusion times is combined with a turbo spin echo sequence for fast NMR imaging (MRI). A fitting function is suggested to describe the time dependence of the apparent diffusion constant in porous (bio-)materials, even if the time range of the apparent diffusion coefficient is limited due to relaxation of the magnetization. The method is demonstrated by characterizing anisotropic cell dimensions and permeability on a subpixel level of different tissues of a carrot (Daucus carota) taproot in the radial and axial directions
    Quantitative NME microscopy of iron transport in methanogenic aggregates
    Vergeldt, F.J. ; Bartacek, J. ; Gerkema, E. ; Osuma, B. ; Philippi, J.G.M. ; Lens, P. ; As, H. van - \ 2009
    Diffusion Fundamentals 10 (2009). - ISSN 1862-4138 - p. 31.1 - 31.4.
    Transport of micronutrients (iron, cobalt, nickel, etc.) within biofilms matrixes such as methanogenic granules is of high importance, because these are either essential or toxic for the microorganisms living inside the biofilm. The present study demonstrates quantitative measurements of metal transport inside these biofilms using T1 weighted 3D RARE. It is shown that iron(II)-EDTA diffusion within the granule is independent of direction or the inner structure of the granules. Assuming position dependence of the spin-lattice relaxivity, Fick’s law for diffusion in a sphere can be applied to simulate the diffusion within the methanogenic granules under investigation. A relatively low diffusion coefficient of 2.5*10-11 m2·s-1 was obtained for iron diffusion within the methanogenic granule
    Magnetic resonance microscopy of iron transport in methanogenic granules
    Bartacek, J. ; Vergeldt, F.J. ; Gerkema, E. ; Jenicek, P. ; Lens, P. ; As, H. van - \ 2009
    Journal of Magnetic Resonance 200 (2009)2. - ISSN 1090-7807 - p. 303 - 312.
    heavy-metal uptake - porous-media - nmr - biofilm - sludge - diffusion - complexes - alginate - immobilization - biosorbents
    Interactions between anaerobic biofilms and heavy metals such as iron, cobalt or nickel are largely unknown. Magnetic resonance imaging (MRI) is a non-invasive method that allows in situ studies of metal transport within biofilm matrixes. The present study investigates quantitatively the penetration of iron (1.75 mM) bound to ethylenediaminetetraacetate (EDTA) into the methanogenic granules (spherical biofilm). A spatial resolution of 109 × 109 × 218 µm3 and a temporal resolution of 11 min are achieved with 3D Turbo Spin Echo (TSE) measurements. The longitudinal relaxivity, i.e. the slope the dependence of the relaxation rate (1/T1) on the concentration of paramagnetic metal ions, was used to measure temporal changes in iron concentration in the methanogenic granules. It took up to 300 min for the iron–EDTA complex ([FeEDTA]2-) to penetrate into the methanogenic granules (3–4 mm in diameter). The diffusion was equally fast in all directions with irregularities such as diffusion-facilitating channels and diffusion-resistant zones. Despite these irregularities, the overall process could be modeled using Fick’s equations for diffusion in a sphere, because immobilization of [FeEDTA]2- in the granular matrix (or the presence of a reactive barrier) was not observed. The effective diffusion coefficient (Dejf) of [FeEDTA]2- was found to be 2.8 × 10-11 m2 s-1, i.e. approximately 4% of Dejf of [FeEDTA]2- in water. The Fickian model did not correspond to the processes taking place in the core of the granule (3–5% of the total volume of the granule), where up to 25% over-saturation by iron (compare to the concentration in the bulk solution) occurred
    Most water in the tomato truss is imported through the xylem, not the phloem. An NMR flow imaging study
    Windt, C.W. ; Gerkema, E. ; As, H. van - \ 2009
    Plant Physiology 151 (2009)2. - ISSN 0032-0889 - p. 830 - 842.
    vapor-pressure deficit - membrane-permeability - transpiration flows - biological tissues - ricinus-communis - grape berries - fruit-growth - sap flow - transport - plants
    In this study, we demonstrate nuclear magnetic resonance flow imaging of xylem and phloem transport toward a developing tomato (Solanum lycopersicum) truss. During an 8-week period of growth, we measured phloem and xylem fluxes in the truss stalk, aiming to distinguish the contributions of the two transport tissues and draw up a balance between influx and efflux. It is commonly estimated that about 90% of the water reaches the fruit by the phloem and the remaining 10% by the xylem. The xylem is thought to become dysfunctional at an early stage of fruit development. However, our results do not corroborate these findings. On the contrary, we found that xylem transport into the truss remained functional throughout the 8 weeks of growth. During that time, at least 75% of the net influx into the fruit occurred through the external xylem and about 25% via the perimedullary region, which contains both phloem and xylem. About one-half of the net influx was lost due to evaporation. Halfway through truss development, a xylem backflow appeared. As the truss matured, the percentage of xylem water that circulated into the truss and out again increased in comparison with the net uptake, but no net loss of water from the truss was observed. The circulation of xylem water continued even after the fruits and pedicels were removed. This indicates that neither of them was involved in generating or conducting the circulation of sap. Only when the main axis of the peduncle was cut back did the circulation stop
    The effect of rice kernel microstructure on cooking behaviour: A combined µ-CT and MRI study
    Mohoric, A. ; Vergeldt, F.J. ; Gerkema, E. ; Dalen, G. van; Doel, L.R. van den; Vliet, L.J. van; As, H. van; Duynhoven, J.P.M. van - \ 2009
    Food Chemistry 115 (2009)4. - ISSN 0308-8146 - p. 1491 - 1499.
    magnetic-resonance - water migration - puffed rice - nmr - grain - gelatinization - starch - profile - flour - model
    In order to establish the underlying structure-dependent principles of instant cooking rice, a detailed investigation was carried out on rice kernels that were processed in eight different manners. Milling, parboiling, wet-processing and extrusion were applied, with and without a subsequent puffing treatment. The mesostructure of the rice kernels was examined by DSC and XRD, and the microstructure by µ-CT. Hydration behaviour during cooking was studied by MRI in a real-time manner. Based on simple descriptive models, three different classes of cooking behaviour can be discerned. The water ingress profiles during cooking of these three classes matched well with simulations from a model that was based on water demand of the starch mass and the porous microstructure of the kernels. Thus a clear correlation between meso/microstructure of a rice kernel and the cooking behaviour has been established
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