NMR Studies on Cellulose and Plant Cell Walls

Since the 1980s, nuclear magnetic resonance (NMR) spectroscopy has been a highly informative method for determining both the structures and conformations of cell-wall polymers and their arrangement within the intact cell wall. Until the early 2000s, solid-state NMR experiments on cell walls generated one-dimensional spectra with limited resolution. The subsequent introduction of multidimensional solid-state NMR methods afforded much more spectral resolution, robust identification of specific signals for each carbon within each polymer molecule and improved possibilities for estimating the distances between individual polymer components of the cell wall. These methods made it possible to show that the structures of the more ordered domains of cellulose microfibrils in the cell walls of higher plants differ from the known forms of crystalline cellulose. It was found that xylans form a close, ordered association with cellulose in secondary cell walls and that pectins, but not most xyloglucans, associate spatially with cellulose in dicot primary cell walls. The rigidity of cell-wall polymers can be estimated by NMR relaxation experiments in both 1D and 2D NMR. Some suggestions are offered for future developments in our understanding of cell-wall structure by new applications of NMR methods.