A14N Nuclear Magnetic Resonance Study of Inorganic Nitrogen Métabolism in Barley, Maize and Pea Roots

Abstract

^l4N nuclear magnetic resonance (NMR) spectroscopy was used to detect simple nitrogen compounds in root tissues from barley (Hordeum vulgare), maize (Zea mays) and pea (Pisum sativum) seedlings. The spectra included contributions from amino and amide groups but, as expected, these peaks were broad and poorly defined in comparison with the resonances from nitrate and ammonium. A quantitative analysis of the spectra of nitrate-grown barley roots showed that the nitrate resonance intensity accounted for the total nitrate content of the tissue. Timecourses of the tissue nitrate intensity in response to changes in the external nitrate composition followed single exponentials, and could be discussed in terms of nitrate exchange and possibly reduction. There was no evidence from these data, or from spin-lattice relaxation measurements, for the existence of more than one large pool of nitrate in the roots, and the results were consistent with a model in which the bulk of the nitrate is vacuolar. In contrast, timecourses of the ammonium resonance in ammonium-grown barley roots were biphasic under certain external conditions, suggesting some form of compartmentation of ammonium in the tissue.