Published Research - Department of Chemistry


Date of this Version



Published in Proc. Natl. Acad. Sci. USA Vol. 81, pp. 748-752, February 1984. Used by Permission


Proton nuclear magnetic resonance (1H NMR) spectra of leaves from 50 plant species were obtained at a spectrometer frequency of 470 MHz. Water present in leaf samples gives rise to characteristic spectral patterns. Most species show only one broad 1H NMR peak; however, the leaves of some plants display complex, orientation-dependent spectra in which a common three-line pattern is discerned. The pattern varies with the angle between the leaf surface and the external magnetic field. Proton relaxation measurements show the presence of at least two water compartments in the leaves. The compartments are responsible for different components of the spectral pattern. EPR spectra, obtained at 35 GHz and at a temperature of -180°C, of plant leaf sections are dominated by the strong signals of manganous ions. We find that most plant leaves have isotropic Mn2+ EPR spectra. However, in some species (including ones that exhibit orientation-dependent 1H NMR spectra) we detect orientation-dependent intensities in the forbidden lines; the spectra indicate that Mn2+ ions occupy binding sites with axial or lower symmetry on nonrandomly oriented membranes. Both the NMR and the EPR results suggest that the chloroplasts of some plants are preferentially aligned with respect to the leaf surface.

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