Structure of Plant Cell Walls

This paper describes the isolation and characterization of rhamnogalacturonan II, a hitherto unobserved component of the primary cell walls of dicotyledonous plants. Rhamnogalacturonan II constitutes 3 to 4% of the primary cell walls of suspension-cultured sycamore (Acer pseudoplatanus) cells. Rhamnogalacturonan II is a very complex polysaccharide yielding, upon hydrolysis, 10 different monosaccharides including the rarely observed sugars apiose, 2-O-methylxylose, and 2-O-methylfucose. In addition, rhamnogalacturonan II is characterized by the rarely observed glycosyl interconnections of 2-linked glucuronosyl, 3,4-linked fucosyl, and 3-linked rhamnosyl residues. These glycosyl linkages have never previously been detected in primary sycamore cell walls. Evidence is presented which suggests that polysaccharides similar to rhamnogalacturonan II are present in the primary cell walls of the three other dicotyledonous plants examined.