Some plant leaves have orientation-dependent EPR and NMR spectra

Publisher Website
Google Scholar
Abstract
Proton NMR (1H NMR) spectra of leaves from 50 plant species were obtained at a spectrometer frequency of 470 MHz. Water present in leaf samples give rise to characteristic spectral patterns. Most species show only 1 broad 1H NMR peak; however, the leaves of some plants display complex, orientation-dependent spectra in which a common 3-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 2 water compartments in the leaves. The compartments are responsible for different components of the spectra pattern. EPR spectra, obtained at 35 GHz and at a temperature of -180.degree. C, of plant leaf sections are dominated by the strong signals of Mn ions. Most plant leaves have isotropic Mg2+ EPR spectra. However, in some species (including ones that exhibit orientation-dependent 1H NMR spectra) orientation-dependent intensities were detected in the forbidden lines; the spectra indicate that Mn2+ ions occupy binding sites with axial or lower symmetry on non-randomly 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.