Structure and Properties of Acidic Polysaccharides from Mung Bean Hypocotyls

Two classes of pectins exhibiting significant structural differences were extracted sequentially from young and mature tissues of the mung bean hypocotyl. 1H- and 13C-N.M.R. analysis of intact polymers revealed that, even in dilute solutions (6 g-liter-1), only a fraction of the galacturonic acid molecules gave significant signals, probably as the result of multi-chain aggregation processes. In contrast, neutral sugars could easily be detected and the data obtained with water-soluble pectins suggested the occurrence of branched blocks with both galactosyl and arabinosyl side-chains. Potentiometric measurements showed that solubilization of the pectins did not significantly change their physicochemical properties. Affinity of the pectins for calcium increased during maturation of the cell wall. Moreover, the changes of the pectin molecules entailed a stronger cohesion within the polysaccharide network. These modifications of the pectins may participate in the process of stiffening the cell wall which takes place along the hypocotyl.