The NMR probehead is a key element of the receiving chain of an NMR spectrometer. To optimize the signal-to-noise ratio the probehead must be adapted for the specific application. This article describes the basic physics and characteristics of NMR probeheads for in vivo applications in small animals and plants as well as quality control procedures on the workbench and in the NMR spectrometer. Various probeheads including volume coils, surface coils, double tuned coils, and microscopy coils are presented and illustrated by results of specific in vivo applications. (C) 2000 John Wiley & Sons. Inc.

The unloading of sucrose in the apical part of the hypocotyl of Ricinus communis L. seedlings was measured by 13C-nuclear magnetic resonance (NMR) spectroscopy. The cotyledons of the seedling were immersed in 5 mM Mes buffer containing 100 mM 13C-labeled sucrose. At intervals of 70–90 min, 13C-NMR spectra with broadband decoupling and nuclear Overhauser enhancement were acquired in vivo. The spectra showed growing 13C-resonances of the labeled positions in the sucrose molecule reaching steady-state labeling within 7–8 h. The specific 13C labeling of sucrose in the G1-position changed from 0.38 in the supplied sucrose solution to 0.16 in the sucrose extracted from the hypocotyl piece at the end of the experiment (13 h). Labeling of starch (and other insolubles) in the hypocotyl piece was ca. 0.10. It is proposed that the decreased specific labeling of unloaded sucrose is mostly due to the separate local pools of sucrose in the cortex and pith parenchyma, respectively, and less to continuous starch degradation and conversion to sucrose. The report gives an example of the application of 13C-NMR spectroscopy in assimilate allocation studies.

. The sucrose concentration was measured at 70-min intervals in the phloem of individual bundles of the hypocotyl of Ricinus seedlings by 1 H nuclear magnetic resonance (NMR) spectroscopic imaging. The sucrose concentration stayed fairly constant in all bundles for more than 7 h if the cotyledons were embedded in the endosperm or excised and incubated in 100 mM sucrose. If, however, the sucrose solution was replaced by sucrose-free buffer solution, the sucrose levels in the phloem decreased with a kinetic depending on the seedling: in some cases there was a smooth decline, in some a decline followed by a slight recovery and in some cases a clear-cut oscillation. The sucrose concentration was often not identical in the phloem of the individual bundles. The oscillations were larger in the phloem at the apex of the hypocotyl than in the phloem at the base of the hypocotyl. Cutting the petiole of one cotyledon led to a decrease in sucrose not only in the four bundles directly connected to the severed petiole but in all eight bundles of the hypocotyl. Cutting the petiole and dividing the vascular ring at the cotyledonary node and at the root crown did not prevent the decline of sucrose in all eight bundles. Therefore, a functional equilibration of translocated solutes between the eight bundles may occur within the 1-h measuring interval by radial diffusion through the parenchyma of the hypocotyl.