Polymer mobility in cell walls of cucumber hypocotyls

Cell walls were prepared from the growing region of cucumber (Cucumis sativus) hypocotyls and examined by solid-state (13)C NMR spectroscopy; in both enzymically active and inactivated states. The rigidity of individual polymer segments within the hydrated cell walls was assessed from the proton magnetic relaxation parameter, T(2), and from the kinetics of cross-polarisation from (1)H to (13)C. The microfibrils, including most of the xyloglucan in the eel wall, as well as cellulose, behaved as very rigid solids. A minor xyloglucan fraction, which may correspond to cross-links between microfibrils, shared a lower level of rigidity with some of the pectic galacturonan. Other pectins, including most of the galactan side-chain residues of rhamnogalacturonan I, were much more mobile and behaved in a manner intermediate between 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.