PECTIC POLYSACCHARIDES OF MESOPHYLL CELL-WALLS OF PERENNIAL RYEGRASS LEAVES

Extraction of mesophyll cell walls from leaves of perennial ryegrass with CDTA, a chelating agent, removed 25 mg uronic acid g(-1), largely in the form of a polymer which spontaneously precipitated on removal of the CDTA or during subsequent purification. Methylation analysis, before and after reduction, showed that the precipitated polymer was a 1,4-linked homogalacturonan essentially free from neutral sugar residues, with a low degree of acetylation (3.6%) and methyl esterification (3.3%). Hot water (HW) extracted further acidic material (5 mg uronide g(-1) cell wall) which could be resolved by ion-exchange chromatography into neutral mixed-linked glucan and bound rhamnogalacturonan fractions. The latter co-chromatographed with sugar residues typical of 3-, 4- and 6-linked galactan and arabinoxylan. Pectin esterase promoted the release from cell walls of HW-soluble rhamnogalacturonan by polygalacturonase, but had no effect on the release of CDTA-soluble uronide. The presence of both homogalacturonan and rhamnogalcturonan, typical of dicotyledons, suggested that the pectic polysaccharides of the Gramineae differed from those of other plants in amount only, rather than nature.