Structure of Plant Cell Walls

Abstract

The purification and characterization of a pectic polymer, rhamnogalacturonan I, present in the primary cell walls of dicots was described. Rhamnogalacturonan I accounted for approximately 7% of the mass of the walls isolated from suspension-cultured sycamore cells. As purified, rhamnogalacturonan I had a MW of approximately 200,000 and was composed primarily of L-rhamnosyl, D-galacturonosyl, L-arabinosyl and D-galactosyl residues. The backbone of rhamnogalacturonan I was composed predominantly of D-galacturonosyl and L-rhamnosyl residues in a ratio of approximately 2:1. About half of the L-rhamnosyl residues were 2-linked and were glycosidically attached to C4 of a D-galacturonosyl residue. The other half of the L-rhamnosyl residues are 2,4-linked and have a D-galacturonosyl residue glycosidically attached at C2. Sidechains averaging 6 residues in length are attached to C4 of the L-rhamnosyl residues. There were many different sidechains, containing variously linked L-arabinosyl, and/or D-galactosyl residues.