The walls of Pteridophytes contain the borate cross-linked pectic polysaccharide rhamnogalacturonan II.

Abstract

Rhamnogalacturonan II (RG-II) is a pectic polysaccharide present in the primary cell walls of all seed plants examined to date. RG-II exists in the primary wall predominantly as a dimer (dRG-II-B) that is cross linked by a 1:2 borate-diol ester. Cross-linking of pectin by this ester regulates wall porosity and thickness and is required for normal plant growth. Little is known about the occurrence of dRG-II-B in the walls of Pteridophytes and Brophytes. We have used LC-ICP-MS to determine the amounts of B and dRG-II-B in the walls of Pteridophytes (lycopods, ferns, whisk ferns, and horsetails) and Bryophytes (mosses, liverworts and hornworts). Pteridophytes and seed plants contain comparable amounts of dRG-II-B. The structures of their RG-IIs are similar but not identical. In contrast, Bryophyte walls contain about 60% less B and <1% of the amount of dRG-II-B present in the walls of seed plants.