Characterization of Paramagnetic Species in Seeds by Electron Paramagnetic Resonance (EPR)

Paramagnetic species were characterized in the seeds of radish wild, rice, mustard, wheat, oats, sorghum, sunflower, soybean, cotton, beans, maize and barley by Electron Paramagnetic Resonance (EPR). Some iron complexes such as goethite, hematite, magnetite, and ferrihydrite, normally present in the soil, were also investigated by EPR, since their signals can, a priori, be present in EPR spectra of seeds. The EPR experiments were performed at X-band microwave frequency (9.3 GHz) on the JEOL spectrometer (JES-PE-3X) from 77 to 385 K and on the BRUKER spectrometer (Elexsys E-580) in a temperature range from 30 to 70 K. In the EPR spectra of the seeds, it was detected the same complex of Fe3+ found in goethite, with g=2.0±0.1 in all the investigated seeds. In addition, free radicals have also been detected with g=2.004±0.002, on all seeds, and with g=2.013 only in sorghum seeds. The sunflower seeds showed the highest signal intensity of the free radical. During the temperature variation, changes were observed in the spectra, in a manner that at low temperature (30 K), beyond the higher intensity on signal of the goethite and free radical, the spectra of the seeds also showed signal of hematite and traces of Mn2+.