Intact plant MRI for the study of cell water relations, membrane permeability, cell-to-cell and long distance water transport. J Exp Bot

Laboratory of Biophysics and Wageningen NMR Centre, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands.
Journal of Experimental Botany (Impact Factor: 5.53). 02/2007; 58(4):743-56. DOI: 10.1093/jxb/erl157
Source: PubMed


Water content and hydraulic conductivity, including transport within cells, over membranes, cell-to-cell, and long-distance
xylem and phloem transport, are strongly affected by plant water stress. By being able to measure these transport processes
non-invasely in the intact plant situation in relation to the plant (cell) water balance, it will be possible explicitly or
implicitly to examine many aspects of plant function, plant performance, and stress responses. Nuclear magnetic resonance
imaging (MRI) techniques are now available that allow studying plant hydraulics on different length scales within intact plants.
The information within MRI images can be manipulated in such a way that cell compartment size, water membrane permeability,
water cell-to-cell transport, and xylem and phloem flow hydraulics are obtained in addition to anatomical information. These
techniques are non-destructive and non-invasive and can be used to study the dynamics of plant water relations and water transport,
for example, as a function of environmental (stress) conditions. An overview of NMR and MRI methods to measure such information
is presented and hardware solutions for minimal invasive intact plant MRI are discussed.

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Available from: Henk Van As
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    • "Water fluxes during freezing and thawing | Page 3 of 12 radial water fluxes during freeze–thaw events (Zweifel et al., 2000; Améglio et al., 2001, 2003); (ii) nuclear magnetic resonance imaging (MRI) allowing visualization of the liquid water allocation before and after freeze–thaw cycles (Faust et al., 1997; Holbrook et al., 2001; Clearwater and Clark, 2003; Van As, 2007); (iiii) X-ray microtomography to visualize embolism inside plants, and also during freezing; this has been performed previously with drought-stressed plants (Brodersen et al., 2010; Charra-Vaskou et al., 2012a; Dalla- Salda et al., 2014; Torres-Ruiz et al., 2014), and is now becoming a reference technology in order to measure embolism in plants without cutting artifacts (Wheeler et al., 2013; Cochard et al., 2014); and (iv) UE measurement to analyze the dynamics of cavitation events (Ponomarenko et al., 2014) during freeze–thaw cycles (Charrier et al., 2015b). "
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    ABSTRACT: Freeze-thaw cycles induce major hydraulic changes due to liquid-to-ice transition within tree stems. The very low water potential at the ice-liquid interface is crucial as it may cause lysis of living cells as well as water fluxes and embolism in sap conduits, which impacts whole tree-water relations. We investigated water fluxes induced by ice formation during freeze-thaw cycles in Juglans regia L. stems using four non-invasive and complementary approaches: a microdendrometer, magnetic resonance imaging, X-ray microtomography, and ultrasonic acoustic emissions analysis. When the temperature dropped, ice nucleation occurred, probably in the cambium or pith areas, inducing high water potential gradients within the stem. The water was therefore redistributed within the stem toward the ice front. We could thus observe dehydration of the bark's living cells leading to drastic shrinkage of this tissue, as well as high tension within wood conduits reaching the cavitation threshold in sap vessels. Ultrasonic emissions, which were strictly emitted only during freezing, indicated cavitation events (i.e. bubble formation) following ice formation in the xylem sap. However, embolism formation (i.e. bubble expansion) in stems was observed only on thawing via X-ray microtomography for the first time on the same sample. Ultrasonic emissions were detected during freezing and were not directly related to embolism formation. These results provide new insights into the complex process and dynamics of water movements and ice formation during freeze-thaw cycles in tree stems.
    Full-text · Article · Nov 2015 · Journal of Experimental Botany
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    • "The light response of individual wheat grains was monitored via MRI, tracking a number of grains over an 18-h period (6 h of dark, 6 h of light, and 6 h of dark). The T2 value, which reflects a combination of water content and cell size in living tissue (Van der Weerd et al., 2002; Van As, 2007), rose statistically significantly in response to illumination (Student's t test, P , 0.05; Fig. 2A), implying an increase in the water content/cell size of the grain (Krishnan et al., 2004, 2014). Image analysis revealed that changes in T2 were confined to small regions of the wheat grains (from 0.63 to 0.78 mm 3 ; Fig. 2B), colocalizing with the crease (Fig. 2, C–E). "
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    ABSTRACT: Here, we have characterized the spatial heterogeneity of the cereal grain's metabolism, and demonstrated how, by integrating a distinct set of metabolic strategies, the grain has evolved to become an almost perfect entity for carbon storage. In vivo imaging revealed light-induced cycles in assimilate supply toward the ear/grain of barley (Hordeum vulgare) and wheat (Triticum aestivum). In silico modelling predicted that in the two grain storage organs (the endosperm and embryo) the light-induced shift in solute influx does cause adjustment in metabolic flux without changes in pathway utilization patterns. The enveloping, leaf-like pericarp, in contrast, shows major shifts in flux distribution (starch metabolism, photosynthesis, remobilization, TCA cycle activity), allows to re-fix 79% of the CO2 released by the endosperm and embryo, allowing the grain to achieve an extraordinary high carbon conversion efficiency of 95%. Shading experiments demonstrated that ears are autonomously able to raise the influx of solutes in response to light, but with little effect on the steady state levels of metabolites or transcripts, or on the pattern of sugar distribution within the grain. The finding suggests the presence of a mechanism(s) able to ensure metabolic homeostasis in the face of short-term environmental fluctuation. The proposed multi-component modeling approach is informative for predicting the metabolic effects of either an altered level of incident light or a momentary change in the supply of sucrose. It is therefore of potential value for assessing the impact of either breeding and/or biotechnological interventions aimed at increasing grain yield.
    Full-text · Article · Sep 2015 · Plant physiology
    • "cannot be explained only by changes in cell sizes. Other phenomena may be the causes of these variations [10]. For instance, the permeability of cell membranes may vary inside tissues and between cultivars. "
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    ABSTRACT: Water status and distribution at subcellular level in whole apple fruit were evaluated by Magnetic Resonance Imaging (MRI) measurement of the multi-exponential transverse (T2) relaxation of water protons. Apparent microporosity, also estimated by MRI, provided mapping of gas distribution in fruit tissues. Measuring for the first time the multi-exponential relaxation of water and apparent tissue microporosity in whole fruit and combining these with histological measurements provided a more reliable interpretation of the origins of variations in the transverse relaxation time (T2) and better characterization of the fruit tissue. Measurements were performed on 54 fruit from 3 different cultivars. Fruit of different sizes were selected for each cultivar to provide tissues with cells of different dimensions. Macrovision measurements were carried out on parenchymal tissue from all fruit to investigate the impact of cell morphology and cell size of all samples on T2 value. The results showed that the MRI transverse relaxation signal is well fitted by a tri-exponential decay curve that reflects cell compartmentalization. Variations in cell size partially explained the different T2 observed. This study highlighted the heterogeneity of apple tissues in terms of relaxation parameters, apparent microporosity and cell morphology and in relation to specific variations between fruit of different cultivars. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Feb 2015 · Magnetic Resonance Imaging
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