J.E.M. Snaar

Probing water compartments and membrane permeability in plant cells by 1H NMR relaxation measurements

(1)H NMR relaxation times (T(1) and T(2)) in parenchyma tissue of apple can identify three populations of water with different relaxation characteristics. By following the uptake of Mn(2+) ions in the tissue it is shown that the observed relaxation times originate from particular water compartments: the vacuole, the cytoplasm, and the cell wall/extracellular space.Proton exchange between these compartments is controlled by the plasmalemma and tonoplast membranes. During the Mn(2+) penetration experiment, conditions occur that cause the relaxation times of protons of cytoplasmic water to be much shorter than their residence time in the cytoplasm. Then the tonoplast permeability coefficient P(d) for water can be calculated from the vacuolar T(1) and T(2) values to be 2.44 10(-5) m.s(-1).

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.

A method for the simultaneous measurement of NMR spin-lattice and spin-spin relaxation times in compartmentalized systems.

Abstract A method for simultaneous measurement of spin-lattice and spin-spin relaxation times of water in compartmentalized systems is presented. The method is based on a combination of the saturation-recovery and the Carr-Purcell-Meiboom-Gill sequences (SR-CPMG). The result is a two-dimensional data set. The data set can be analyzed in different ways, i.e., in a conventional way yielding the values of T1 and T2 present in the system, or in a way yielding correlated T1 and T2 values for each compartment. The observed relaxation times are the intrinsic relaxation times of the compartments if exchange between the compartments is absent, or additionally affected by exchange, as is demonstrated using two phantoms: (i) two concentric tubes containing nonexchanging MnCl2 solutions of different concentration and (ii) apple fruit tissue, containing water in compartments exhibiting mutual exchange. For (i), the SR-CPMG sequence results in a better S N ratio for the fit of T1 and in the corresponding intrinsic T1 and T2 values of the MnCl2 solutions in each tube. For (ii), the observed relaxation times reflect the exchange kinetics of water between the compartments in addition to the intrinsic T1 and T2 relaxation times in those compartments.

Localized real time blood flow measurements

A novel method for real time, localized, flow measurements is applied to blood flow in human fingers. Results for arterial and venous flow in normal subjects and patients with abnormal blood circulation are presented. Effects of blood flow regulation by the autonomic nervous system have been observed. Stricture of the digital arteries could be clearly demonstrated in a patient with Raynauds phenomenon. Experimental signals due to pulsatile flow in a model system can be simulated in a quantitative way. The calibration, however, depends on the actual spin-spin relaxation time and the shape of the pulsatile flow vs. time curve. Due to these limitations, the volume flow rate can be measured with a relative error of approximately +/- 25%.