Biosynthesis and cell-wall deposition of a pectin-xyloglucan complex in pea

Abstract

Golgi-enriched enzyme preparations prepared from etiolated pea epicotyls incorporated [U−14C]galactose from UDP-[U−14C]galactose into the 1,4-β-galactan sidechains of a pectin–xyloglucan complex. This complex could bind to paper and was degraded both by pectin-degrading enzymes and by a xyloglucan-specific endoglucanase. Gel permeation chromatography was used to assess the molecular size of the complex and of enzymically-degraded, galactan-containing fragments of it. Etiolated pea stems were labelled with [U−14C]sucrose for 1 h, and the newly-synthesised cell wall polysaccharides were extracted with EDTA or NaOH and fractionated by ion-exchange chromatography. The NaOH-extracted, acidic radioactive polysaccharides obtained in this way were also degraded both by pectin-degrading enzymes and by xyloglucan-specific endoglucanase. Analysis of the radioactive sugar composition indicated that neutral sugars characteristic of both pectin and xyloglucan were present. Analysis of the total non-radioactive, neutral sugar composition of the NaOH-extracted, acidic cell-wall polysaccharides indicated that pectin–xyloglucan complexes were a general feature of the cell wall in this tissue.