Edo Gerkema

Most Water in the Tomato Truss Is Imported through the Xylem, Not the Phloem: A Nuclear Magnetic Resonance Flow Imaging Study

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.

Quantitative permeability imaging of plant tissues

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.

Anomalies in moisture transport during broccoli drying monitored by MRI

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.

INFRARED TRANSIENT THERMOGRAPHY FOR NON-CONTACT, NONDESTRUCTIVE INSPECTION OF WHOLE AND DISSECTED APPLES AND OF CHERRY TOMATOES AT DIFFERENT MATURITY STAGES

Introduction Fruits and vegetables used in various processed products, as well as in fresh market sales, are expected to comply with the certain quality standards. However. quality is everything but a single parameter state and, therefore, a variety of subjective and objective measurements are usually performed. In particular, the firmness and maturity are considered important attributes to the quality of fruits and vegetable crops. Presently. these parameters are usually determined either destructively (by a pressure tester) or by means of ultrasound; a development of alternative methods has been strongly encouraged in the recent years.

Magnetic resonance microscopy of iron transport in methanogenic granules

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 (1.7 5mM) bound to ethylenediaminetetraacetate (EDTA) into the methanogenic granules (spherical biofilm). A spatial resolution of 109x109x218 microm(3) 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/T(1)) 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 (3-4mm 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 Ficks 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 (D(ejf)) of [FeEDTA](2-) was found to be 2.8x10(-11)m(2)s(-1), i.e. approximately 4% of D(ejf) 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.

Combined analysis of diffusion and relaxation behavior of water in apple parenchyma cells

With apple parenchymal cells as an example, we demonstrate the expedience of combined analysis of the relaxation and diffusion of water molecules in plant cells by NMR spectroscopy. At small diffusion times, our approach discerns three relaxation components pertaining to water in the vacuole, cytoplasm, and intercellular space. The corresponding self-diffusion coefficients are determined. At long diffusion times, it is possible to distinguish two components. For the slow-relaxing component (vacuolar water) we observe the mode of restricted diffusion. For the fast-relaxing components, the diffusion coefficient anomalously increases with time.

The impact of metal transport processes on bioavailability of free and complex metal ions in methanogenic granular sludge

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.

Phloem flow and sugar transport in Ricinus communis L. is inhibited under anoxic conditions of shoot or roots

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 δ(13) C 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 in Soils: Determination of Water Content Changes Due to Root Water Uptake by Means of a Multi-Slice-Multi-Echo Sequence (MSME)

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 di- ameter 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 co- registration 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.

Real-time and in situ determination of ammonia concentrations in the atmosphere by means of intermodulated stark resonant CO2 laser photoacoustic spectroscopy

Abstract A concept of Intermodulated Photoacoustic Stark Spectroscopy (IMPASS) was used in an attempt to perform the interference-free field measurement of trace ammonia (3–40 ppbv) concentration levels in the air with a time resolution of 40 s.