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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    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.
    MRI of plants and foods
    As, H. van; Duynhoven, J.P.M. van - \ 2013
    Journal of Magnetic Resonance 229 (2013). - ISSN 1090-7807 - p. 25 - 34.
    nuclear-magnetic-resonance - distance water transport - stem diameter variations - nmr-spectroscopy - imaging system - self-diffusion - porous-media - rheo-nmr - pfg-nmr - flow
    The importance and prospects for MRI as applied to intact plants and to foods are presented in view of one of humanity's most pressing concerns, the sustainable and healthy feeding of a worldwide increasing population. Intact plants and foods have in common that their functionality is determined by complex multiple length scale architectures. Intact plants have an additional level of complexity since they are living systems which critically depend on transport and signalling processes between and within tissues and organs. The combination of recent cutting-edge technical advances and integration of MRI accessible parameters has the perspective to contribute to breakthroughs in understanding complex regulatory plant performance mechanisms. In food science and technology MRI allows for quantitative multi-length scale structural assessment of food systems, non-invasive monitoring of heat and mass transport during shelf-life and processing, and for a unique view on food properties under shear. These MRI applications are powerful enablers of rationally (re)designed food formulations and processes. Limitations and bottlenecks of the present plant and food MRI methods are mainly related to short T-2 values and susceptibility artefacts originating from small air spaces in tissues/materials. We envisage cross-fertilisation of solutions to overcome these hurdles in MRI applications in plants and foods. For both application areas we witness a development where MRI is moving from highly specialised equipment to mobile and downscaled versions to be used by a broad user base in the field, greenhouse, food laboratory or factory. (C) 2013 Elsevier Inc. All rights reserved.
    Flow characteristics and exchange in complex biological systems as observed by pulsed-field-gradient magnetic-resonance imaging
    Homan, N. ; Venne, B.B. ; As, H. van - \ 2010
    Physical Review. E, Statistical nonlinear, and soft matter physics 82 (2010)2. - ISSN 1539-3755
    distance water transport - pfg nmr - porous-media - membrane-permeability - spatial correlations - self-diffusion - mri - relaxation - dispersion - sequence
    Water flow through model porous media was studied in the presence of surface relaxation, internal magnetic field inhomogeneities and exchange with stagnant water pools with different relaxation behavior, demonstrating how the apparent flow parameters average velocity, volume flow and flow conducting area in these situations depend on the observation time. To investigate the water exchange process a two component biological model system consisting of water flowing through a biofilm reactor (column packed with methanogenic granular sludge beads) was used, before and after a heat treatment to introduce exchange. We show that correction of the stagnant fluid signal amplitude for relaxation at increasing observation time using the observed relaxation times reveals exchange between the two fractions in the system. Further it is demonstrated how this exchange can be quantified
    Sieve tube geometry in relation to phloem flow
    Mullendore, D.L. ; Windt, C.W. ; As, H. van; Knoblauch, M. - \ 2010
    The Plant Cell 22 (2010)3. - ISSN 1040-4651 - p. 579 - 593.
    distance water transport - ricinus-communis - mass-flow - callose substance - xylem flow - p-protein - translocation - long - mechanism - element
    Sieve elements are one of the least understood cell types in plants. Translocation velocities and volume flow to supply sinks with photoassimilates greatly depend on the geometry of the microfluidic sieve tube system and especially on the anatomy of sieve plates and sieve plate pores. Several models for phloem translocation have been developed, but appropriate data on the geometry of pores, plates, sieve elements, and flow parameters are lacking. We developed a method to clear cells from cytoplasmic constituents to image cell walls by scanning electron microscopy. This method allows high-resolution measurements of sieve element and sieve plate geometries. Sieve tube–specific conductivity and its reduction by callose deposition after injury was calculated for green bean (Phaseolus vulgaris), bamboo (Phyllostachys nuda), squash (Cucurbita maxima), castor bean (Ricinus communis), and tomato (Solanum lycopersicum). Phloem sap velocity measurements by magnetic resonance imaging velocimetry indicate that higher conductivity is not accompanied by a higher velocity. Studies on the temporal development of callose show that small sieve plate pores might be occluded by callose within minutes, but plants containing sieve tubes with large pores need additional mechanisms
    MRI of intact plants
    As, H. van; Scheenen, T. ; Vergeldt, F.J. - \ 2009
    Photosynthesis Research 102 (2009)2-3. - ISSN 0166-8595 - p. 213 - 222.
    nuclear-magnetic-resonance - distance water transport - membrane-permeability - diffusion constants - spin relaxation - nmr microscopy - sap flow - photosynthesis - phloem - xylem
    Nuclear magnetic resonance imaging (MRI) is a non-destructive and non-invasive technique that can be used to acquire two- or even three-dimensional images of intact plants. The information within the images can be manipulated and used to study the dynamics of plant water relations and water transport in the stem, e.g., as a function of environmental (stress) conditions. Non-spatially resolved portable NMR is becoming available to study leaf water content and distribution of water in different (sub-cellular) compartments. These parameters directly relate to stomatal water conductance, CO2 uptake, and photosynthesis. MRI applied on plants is not a straight forward extension of the methods discussed for (bio)medical MRI. This educational review explains the basic physical principles of plant MRI, with a focus on the spatial resolution, factors that determine the spatial resolution, and its unique information for applications in plant water relations that directly relate to plant photosynthetic activity
    0.7 and 3 T MRI and sap flow in intact trees: xylem and phloem in action
    Homan, N. ; Windt, C.W. ; Vergeldt, F.J. ; Gerkema, E. ; As, H. van - \ 2007
    Applied Magnetic Resonance 32 (2007)1-2. - ISSN 0937-9347 - p. 157 - 170.
    nuclear-magnetic-resonance - distance water transport - noninvasive measurement - ricinus-communis - plants - nmr - long - microscopy
    Dedicated magnetic resonance imaging (MRI) hardware is described that allows imaging of sap flow in intact trees with a maximal trunk diameter of 4 cm and height of several meters. This setup is used to investigate xylem and phloem flow in an intact tree quantitatively. Due to the fragile gradients in pressure present in both xylem and phloem, methods to study xylem and phloem transport must be minimally invasive. MRI flow imaging by means of this hardware certainly fulfils this condition. Flow is quantified in terms of (averaged) velocity, volume flow (flux) and flow conducting area, either in imaging mode or as a nonspatially resolved total. Results obtained for one tree, imaged at two different field strengths (0.7 and 3 T), are compared. An overall shortening of observed T2 values is manifest going from 0.7 to 3 T. Although some susceptibility artefacts may be present at 3 T, the results are still reliable and the gain in sensitivity results in shorter measurement time (or higher signal-to-noise ratio) with respect to the 0.7 T system. The results demonstrate that by use of dedicated hardware, xylem and phloem flow and its mutual interaction, can be studied in intact trees in relation to the water balance and in response to environmental (stress) conditions
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