The effect of hydration on the mobility of polysaccharides in onion cell-wall material (CWM) was studied by solid-state NMR. The application of proton T-1 rho, carbon T-1 relaxation measurements, and 2D-WISE (wideline separation) experiments led to a coherent overall picture of the mobility inside the cell wall, combining domain-averaged as well as site-specific motional information. Whereas the mobility of all individual chemical sites increased upon hydration, only the average chain mobility of the pectin was strongly affected, indicating the predominant interaction of water molecules with the pectin. The 2D-WISE experiment revealed a spatial heterogeneity of the polysaccharide dynamics across the sample, showing at least two different motional regimes for pectin and cellulose domains. (C) 1999 Elsevier Science Ltd. All rights reserved.