[Pectic polysaccharides in the stem calli of the rowan tree Sorbus aucuparia L]

The water-soluble polysaccharide fractions SAcI and SAclI were isolated from rowan tree stem calli. The SAcI fraction was shown to contain compounds belonging to the arabinogalactan II group. The SAcII fraction, termed sorban, was found to contain pectic polysaccharides that make up the protopectin complex of the cell wall callusand that had a high content of galacturonic acid residues together with neutral sugars characteristic of rhamnogalacturonan I (RG-I) polysaccharides. Using methylation assays, some structural features of the ramified region of sorban were elucidated. The backbone of sorban was found to consist of 1,4-α-D-galacto-pyranosyluronic acid residues. The neutral sugars are represented by 1,6-linked galactopyranose and 1,5-linked arabinofuranose residues as the primary constituents, as well as 1,6-linked mannopyranose and 1,4-linked glucopyranose and xylopyranose residues. Callus growth was shown to be accompanied by nearly constant quantities of galacturonic acid and neutral sugar residues in sorban (fraction SAcII) from the rowan stem callus.