Monosaccharide compositions of unlignified cell walls of monocotyledons in relation to the occurrence of wall-bound ferulic acid

Abstract

The families of monocotyledons can be divided into two groups on the basis of the presence (Group A) or absence (Group B) of ester-linked ferulic acid in their unlignified cell walls (UCW). In the Poaceae this ferulic acid is linked to glucuronoarabinoxylans, which are major components of these cell walls (CW). The hypothesis was examined that the UCW of the other Group A families also contain glucuronoarabinoxylans as their major noncellulosic polysaccharides, whereas pectic polysaccharides are the major noncellulosic polysaccharides in the UCW of the Group B families. Monosaccharide compositions were determined of UCW from one species in each of nine Group A families, eight Group B families, and, for comparison, two families of dicotyledons. The results mostly supported the hypothesis. The UCW of Group A monocotyledons contained large proportions of arabinose and xylose and greater proportions of glucuronic acid than the CW of Group B. This is consistent with the presence of large proportions of glucuronoarabinoxylans in these CW. In contrast, the UCW of Group B monocotyledons had monosaccharide compositions similar to those of the dicotyledons. They contained large proportions of galactose and galacturonic acid, consistent with the presence of large proportions of pectic polysaccharides. Two Group B species [ Egeria densa (Hydrocharitaceae) and Potamogeton crispus (Potamogetonaceae)] were unusual in having CW containing large proportions of xylose. One Group A species, Phoenix reclinata (Arecaceae) was exceptional in having CW with a monosaccharide composition similar to dicotyledons. The results are discussed in relation to cladograms constructed from DNA nucleotide sequences from the chloroplast gene rbcL and a possible sequence is proposed for the evolution of the composition of UCW of monocotyledons.