3-O-Methylrhamnose in lower land plant primary cell walls

Acid hydrolysis of cell wall-rich material derived from the young photosynthetic tissues of lower land plants and charophytes yielded an unusual sugar. This sugar was identified as 3-O-methylrhamnose (trivial name acofriose) by its ¹H and ¹³C NMR spectra. In addition to the usual major monosaccharides (glucose, galactose, mannose, arabinose, xylose, rhamnose, glucuronic acid and galacturonic acid) acofriose was released from cell walls of three charophytic algae (Chara coralina, Coleochaete scutata and Klebsormidium flaccidium), a hornwort (Anthoceros caucasicus), leafy and thalloid liverworts, mosses and homosporous lycopodiophytes (Lycopodium pinifolium, Huperzia selago and Diphasiastrum alpinum). The yield of acofriose approximately equalled that of rhamnose. Acofriose was not detectable in the cell walls of a heterosporous lycopodiophyte, a eusporangiate fern, or any of several leptosporangiate ferns, gymnosperms and angiosperms. Our results show that the primary cell walls of lower land plants and their charophyte ancestors are qualitatively different from those of higher plants: the loss of rhamnose methylation supports the generalisation that major steps in plant evolution have required significant changes in cell wall composition.