Structure of acid-extractable polysaccharides of tree greenery of Picea abies

•The acid-extractable pectin (PAA fraction) were isolated from P. abies greenery.•RG-I side chains are formed out of branched 1,5-α-L-arabinan and 1,4-β-D-galactan.•PAA fraction contained glycans of the glucuronoarabinoxylan and glucomannan classes.•However, neither glucomannans nor glucuronoarabinoxylans were associated with RG-I. The polysaccharide PAA was isolated from tree greenery of spruce Picea abies by the extraction with HCl solution. Monosaccharide analysis PAA revealed high content of uronic acid residues (45%), arabinose (19.5%) and galactose (8.6%). It was shown that this polysaccharide contained polymers of various structures. The major component of which were pectic polysaccharides represented mainly by partly methyl-esterified and partly acetylated 1,4-α-D-galacturonan and by minor parts of partly 2-O- and/or 3-O- acetylated rhamnogalacturonan-I (RG-I). The side carbohydrate chains of the branched region of RG-I were represented predominantly by highly branched 1,5-α-L-arabinan and minor portions of 1,4-β-D-galactan. In addition to the dominant pectins, the isolated polysaccharide also contained arabinogalactan proteins (AGP) and binding glycans of the glucuronoarabinoxylan (GAX), glucomannan (GM) and xyloglucan classes, which indicated a close interaction of these polysaccharides in the cell walls. It can be concluded that, at least a part of the pectin is strongly associated with the AGP and binding glycans of the GAX and GM classes. However, neither GM nor GAX were associated with RG-I.