P.A. de Jager

Liming effects on the chemical composition of the organic surface layer of a mature Norway spruce stand (Picea abies [L.] Karst

The application of lime in a mature Norway spruce (Picea abies [L.] Karst.) forest in southern Germany induced major changes in the activity of soil organisms and root growth. Since this may influence the chemical compostion of the soil organic matter (SOM) of the organic surface layer, its composition and changes due to the treatment were examined in this study. Fine roots of Norway spruce have a relatively low content of extractable lipids, a low alkyl C content (C-13 CPMAS NMR) and a high ratio of non-cellulosic to cellulosic carbohydrates (NC/CC, carbohydrate determination by MBTH and gas chromatography analyses) as compared to needles. Furthermore, they show high ratios of suberin/cutin compounds (thermally assisted hydrolysis and methylation, (THM)) and high ratios of eicosanic acid/phytadiene I in their lipid extracts (pyrolysis-GC/MS). Liming (4 t ha(-1) dolomite) of a Norway spruce organic surface layer decreased the proportion of alkyl C, the alkyl C/O-alkyl C ratio, and the content of extractable lipids. The NC/CC ratio and the abundance of suberin relative to cutin components increased. The contribution of the chlorophyll component phytadiene I decreased in relation to eicosanic acid. These changes are attributed to increased fine root formation in the organic layer after liming. Furthermore, the presence of less degraded lignin (THM, peak ratio of 3,4-dimethoxybenzoic acid, methyl ester/3,4-dimethoxy-benzaldehyde) on the limed plot is explained by the increased input of relatively fresh fine root material. On the other hand, the decrease in the carbon-to-nitrogen ratio may be attributed to the higher microbial activity after liming

Quantitative measurement and imaging of transport processes in plants and porous media by 1H NMR

NMR and MRI have been applied to transport processes, that is, net flow and diffusion/perfusion, of water in whole plants, cells, and porous materials. By choosing proper time windows and pulse sequences, magnetic resonance imaging can be made selective for each of the two transport processes. For porous media and plant cells the evolution of the spatial distribution of excited spins has been determined by q-space imaging, using a 20 MHz pulsed 1H NMR imager. The results of these experiments are explained by including spin-relaxation and exchange at boundaries. A 10 MHz portable 1H NMR spectrometer is described, particularly suitable to study the response of net flow in plants and canopies to changing external conditions.

The study of flow by pulsed nuclear magnetic resonance. I. Measurement of flow rates in the presence of a stationary phase using a difference method

Abstract An analysis is presented of the effect of plug flow and laminar flow on spin-echo amplitudes in a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, including the rf field distribution of the transmitter/receiver coil. A difference method is described for the measurement of flow rates of flowing fluid in the presence of stationary fluid. Experiments have been carried out on a capillary system with flowing and stationary water, simulating a plant stem. The results are in agreement with a laminary flow in the capillary and a Gaussian shape of the rf field distribution. A discussion is given of the application of the spin-echo difference method to the determination of flow rates in plant stems.

The study of flow by pulsed nuclear magnetic resonance. II. Measurement of flow velocities using a repetitive pulse method

Abstract A pulsed NMR method that makes possible the measurement of flow velocities of flowing fluid is described. The method employs a regular sequence of identical rf pulses and a linear gradient in the static magnetic field in the direction of flow. Flow velocities of laminar flow in a capillary are measured in the region 1 to 25 mm/sec. A theoretical analysis of the pulse method is given, based on the classical Bloch equations and taking into account a linear field gradient of the static magnetic field and an inhomogeneous distribution of the rf field of the transmitter/receiver coil. A comparison is given of experimental NMR signals and computer simulations. Since a null-signal is detected for stationary samples, the method is especially suitable in biological systems where fluid flow takes place in the presence of stationary fluid.

Suppression of spinning sidebands in magic-angle-spinning NMR spectroscopy using 180° pulses: An application to biological systems

It is known that pulse sequences of four 180” pulses can be used to obtain magicangle-spinning (MAS) NMR spectra free of spinning sidebands (1, 2). In a recent paper (3) we reported an alternative in which a single 180” pulse is used to suppress spinning sidebands and a simple theory was presented that accounts for the observed effects. In this communication we will extend our work and show that the single 180” pulse method is a special case of a more general method that makes use of two 180” pulses. A theory will be developed that predicts the intensity of the centerband and spinning sidebands. A comparison will be made of the oneand two-180°-pulse methods applied to MAS 13C NMR of ‘3C-enriched coat protein of cowpea chlorotic mottle virus (CCMV). The starting point of our theoretical analysis is the suppression of first-order spinning sidebands in 13C MAS NMR spectra, since these sidebands are often strong, whereas the secondand higher-order spinning sidebands have much lower intensities. As has been shown previously (3), the first-order spinning sidebands mainly arise from an instantaneous resonance frequency in the rotating frame given by

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 effect of modulation frequency and rotational correlation time on various spectral displays in saturation-transfer ESR spectroscopy. The use of in-phase, quadrature, magnitude, and phase-plot displays

Abstract A saturation-transfer ESR study is carried out on maleimide spin-labeled hemoglobin in various glycerol-water mixtures. The effect of modulation frequency is examined at 12.5, 50, and 100 kHz in combination with various values of the rotational correlation times in the range from 10−7 to 10−4 s. The second-harmonic in-phase and quadrature spectral displays are used to characterize the saturation transfer processes. In addition the phase-insensitive magnitude and phase-plot displays that are directly derived from the in-phase and quadrature displays are discussed. From the experiments it is concluded that all four spectral displays show good sensitivity for molecular motion in the range from 10−7 to 10−4 s for modulation frequencies at 50 and 100 kHz. From computer simulations it follows that higher modulation frequencies up to 500 kHz can lead to a still better sensitivity to molecular motion.

Magic-angle-spinning NMR on solid biological systems. Analysis of the origin of the spectral linewidths

Abstract Magic-angle-spinning (MAS) high-power 1 H-decoupled 13 C and 31 P NMR has been applied to solid biological materials to obtain information about the mechanisms that determine the spectral linewidths. The line broadening in MAS 31 P NMR spectra of solid tobacco mosaic virus (TMV) has been investigated by selective saturation and T 2 measurements. About 90 Hz stems from homogeneous effects, whereas the inhomogeneous contribution is approximately 100 Hz. The inhomogeneous line broadening is assigned to macroscopic inhomogeneities in the sample and not to variations in the nucleotide bases along the RNA strand in TMV. It is concluded that sample preparation is of vital importance for obtaining well-resolved spectra. Under optimal preparation techniques the isotropic values of the chemical shift of the different 31 P sites have been determined to obtain information about the secondary structure of the viral RNA. The chemical shift anisotropy has been determined from the relative intensities of the spinning side bands in the spectra. The chemical shift information is used to make a tentative assignment of the resonance in terms of the three structurally distinguishable phosphate groups in TMV. The origin of the linewidths in MAS NMR has been examined further by 13 C NMR of approximately 10% 13 C-enriched coat protein of cowpea chlorotic mottle virus, using selective excitation and saturation techniques, as well as measurements of the relaxation times T 1 γ and T 2 . The CO resonance in the spectrum is composed of an inhomogeneous and homogeneous part with a total linewidth of 700 Hz. The homogeneous linewidth, contributing with 200 Hz, is found to arise from slow molecular motions in the solid on a millisecond timescale.