Polymer mobility in cell walls of cucumber hypocotyls

Cell walls were prepared from the growing region of cucumber (Cucumis sativ us) hypocotyls and examined by solid-state C-13 NMR spectroscopy; in both e nzymically active and inactivated states. The rigidity of individual polyme r segments within the hydrated cell walls was assessed from the proton magn etic relaxation parameter, T-2, and from the kinetics of cross-polarisation from H-1 to C-13. The microfibrils, including most of the xyloglucan in th e eel wall, as well as cellulose, behaved as very rigid solids. A minor xyl oglucan fraction, which may correspond to cross-links between microfibrils, shared a lower level of rigidity with some of the pectic galacturonan. Oth er pectins, including most of the galactan side-chain residues of rhamnogal acturonan I, were much more mobile and behaved in a manner intermediate bet ween the solid and liquid states. The only difference observed between the enzymically active and inactive cell walls, was the lass of a highly mobile , methyl-esterified galacturonan fraction, as the result of pectinesterase activity. (C) 1999 Elsevier Science Ltd. All rights reserved.