Solid-state 15N NMR analysis of highly 15N-enriched plant materials.

Solid-state 15N NMR spectroscopy was used to determine the chemical nature of nitrogen in 15N-enriched material from the roots and stems of wheat ( Triticum aesitivum), field pea ( Pisum sativum) and kikuyu grass ( Pennisetum clandestinum) and from the roots, stems and leaves of a eucalyptus species ( Eucalyptus globulus). Nitrogen-15 cross polarization (CP) spectra of the materials were all very similar, with 64–75% of total signal assigned to amide N. Spin counting analysis indicated that 37–80% of potential signal was accounted for in the CP spectra, and that NMR observability using the CP technique (N obs -CP) was higher for stems and leaves than for roots, and higher for wheat and eucalyptus than for peas and kikuyu. The 15N direct polarization (DP) spectra contained higher proportions of signal assigned to amine (up to 22%) and nitrate (up to 17%), and less assigned to amide N (50–72%) than the corresponding CP spectra. Spin counting analysis indicated that 68–93% of potential signal was accounted for in the DP spectra, confirming the DP technique to be more quantitatively reliable than CP. [ABSTRACT FROM AUTHOR]