Abstract
BackgroundMultidimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy has emerged as an indispensable technique for resolving polymer structure and intermolecular packing in primary and secondary plant cell walls. Isotope (13C) enrichment provides feasible sensitivity for measuring 2D/3D correlation spectra, but this time-consuming procedure and its associated expenses have restricted the application of ssNMR in lignocellulose analysis.ResultsHere, we present a method that relies on the sensitivity-enhancing technique Dynamic Nuclear Polarization (DNP) to eliminate the need for 13C-labeling. With a 26-fold sensitivity enhancement, a series of 2D 13C–13C correlation spectra were successfully collected using the unlabeled stems of wild-type Oryza sativa (rice). The atomic resolution allows us to observe a large number of intramolecular cross peaks for fully revealing the polymorphic structure of cellulose and xylan. NMR relaxation and dipolar order parameters further suggest a sophisticated change of molecular motions in a ctl1 ctl2 double mutant: both cellulose and xylan have become more dynamic on the nanosecond and microsecond timescale, but the motional amplitudes are uniformly small for both polysaccharides.ConclusionsBy skipping isotopic labeling, the DNP strategy demonstrated here is universally extendable to all lignocellulose materials. This time-efficient method has landed the technical foundation for understanding polysaccharide structure and cell wall assembly in a large variety of plant tissues and species.
Highlights
Multidimensional solid-state nuclear magnetic resonance spectroscopy has emerged as an indispensable technique for resolving polymer structure and intermolecular packing in primary and secondary plant cell walls
These mutations happen to rice CHITINASE-LIKE1 (CTL1) and its homolog CTL2, which have been suggested a role in controlling cellulose biosynthesis, thereby affecting wall integrity [38,39,40,41], as ctl1 and ctl1 ctl2 plants exhibited obvious brittleness phenotypes
Quantitative detection of all carbons is achieved using a recently developed pulse sequence, MultiCP, which counts on 1H T1 relaxation to repeatedly restore 1H magnetization between the many CP blocks included in each individual scan of the experiment [42,43,44]
Summary
Multidimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy has emerged as an indispensable technique for resolving polymer structure and intermolecular packing in primary and secondary plant cell walls. Isotope (13C) enrichment provides feasible sensitivity for measuring 2D/3D correlation spectra, but this time-consuming procedure and its associated expenses have restricted the application of ssNMR in lignocellulose analysis. The past decade has witnessed the rapid advances in multidimensional solid-state NMR (ssNMR) capabilities that have enabled high-resolution characterization of intact plant cell walls. This spectroscopic method provides a wealth of atomic-level information on the conformational structure of polysaccharides, covalent linkage. In vitro replication procedures weaken the merit of ssNMR as an analytical technique targeting natural tissues
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