One- and Two-Dimensional Solid-State NMR Reveals Local Aliphatic Heterogeneity in Native Bark Suberin

Suberin is a protective bark cell-wall polymer whose native organization remains difficult to resolve by extraction-based analysis. Here, a combination of one- and two-dimensional solid-state nuclear magnetic resonance techniques was used to examine native suberin within the intact Salix bark cell-wall material. Major glycerol and fatty-acyl motifs were identified, providing a basis for analyzing local spatial arrangement in native suberin. The characteristic 30 and 33 ppm methylene populations exhibited distinct native environments, with the 30 ppm population showing greater chemical heterogeneity, closer olefinic/aromatic contacts, and higher water accessibility, whereas the 33 ppm population exhibited a largely uniform methylene environment, restricted segmental motion, and reduced effective water accessibility. The two populations coexist within the native suberin matrix but remain partially segregated at the local scale. These data provide a native-state molecular view of aliphatic heterogeneity in bark suberin and refine current models of suberin architecture in plant cell walls.