Fig. 4

DNP enables 2D correlation spectroscopy using unlabeled and native cell walls. a 2D ¹³C–¹³C INADEQUATE spectrum of unlabeled WT rice collected on a 600 MHz/395 GHz DNP system. DNP effectively detects and resolves the signals from cellulose and hemicellulose at natural isotope abundance. Superscripts are used to denote the eight types of glucose units in interior and surface cellulose and the twofold and threefold conformations in xylan. Inset shows the lipid signals that are folded in the indirect dimension. b 2D ¹³C–¹³C INADEQUATE spectrum of ¹³C-labeled WT rice stems measured on a 400 MHz NMR spectrometer. The spectral pattern is comparable to the DNP-assisted natural-abundance spectrum in a. c Arabinose and acetyl signals are detectable using ¹³C-labeled samples, but become invisible in the DNP spectrum of unlabeled materials. d Number of peaks detected using labeled and unlabeled samples, which are tabulated in Additional file 1: Table S3. Asterisks indicate the components that are poorly detected using natural-abundance DNP