Fig. 1
From: Lignin-polysaccharide interactions in plant secondary cell walls revealed by solid-state NMR
The polymorphic structure of lignin and polysaccharides in intact maize stems. a Representative 2D 13C–13C correlation spectrum resolves the polymorphic signals of cellulose and xylan. The xyloglucan (XyG) signals are missing (blue circles), indicating a negligible amount of primary cell walls. Abbreviations are used for assignment, e.g., s4g is carbon 4 of glucose type-g on the microfibril surface. b Representative polysaccharide structures. c Cellulose signals in maize coleoptile and mature stems. The six cellulose allomorphs are labeled using letters a–g. The intensity of type-c cellulose is 2X greater in mature stems compared with coleoptiles. d An illustrative figure of two adjacent microfibrils, with the restructured chains boxed in blue, which increase the intensity of type-c cellulose in c. These chains restructure by changing the hydroxymethyl conformation. The number of glucan chains in the figure may not represent the actual microfibril structure. The aromatic signals of lignin are resolved using 2D 13C–13C spectra measured using e 53-ms CORD and f INADEQUATE methods. g Representative structures and 13C chemical shifts of lignin
