Cell-wall material was isolated from the alcohol-insoluble residue of carrot by treatment with Pronase, phenol-acetic acid-water, and aqueous 90% methyl sulphoxide. Some pectic material was solubilised, but the major component was a highly esterified, acidic arabinogalactan.
The purified cell-wall material, which contained -1% of protein, was sequentially extracted with water at 80", ammonium oxalate at 80", and M and 4M KOH at 20", to leave a residue of a-cellulose, which contained some pectic material. From the hot-water-soluble fraction, a major pectic polymer was isolated by anion-exchange chromatography.
Methylation analysis showed that it was a rhamnogalacturonan, probably having highly branched arabinan and slightly branched galactan side-chains linked to O-4 of rhamnopyranonyl residues. An unusual feature of this pectic polymer is that it contained a small but significant proportion of 1,Clinked xylopyranosyl residues. From the alkali-soluble fractions, a range of pectic polymers associated with various amounts of xylans and possibly xyloglucans was isolated. The main linkages present in these complexes were 1,6linked galactopyranosyluronic acid, 1,Clinked galactopyranosyl, and 1,5linked arabinofuranosyl residues, terminal arabinofuranosyl and galactopyranosyl groups, and, in some fractions, 1,Clinked xylopyranosyl residues. The possible association of some of these polymers with proteins and phenolics is discussed.