The polysaccharide composition of Poales cell walls

Abstract

Abstract Monocotyledon families can be divided into two groups depending on the presence (Group A) or absence (Group B) of ferulic acid ester-linked to their unlignified cell walls. The two groups also differ in the major types of non-cellulosic polysaccharides in their unlignified cell walls: in Group A they are glucuronoarabinoxylans (GAXs), and in Group B they are pectic polysaccharides. Previous studies suggested that among the Group A families, the Poaceae (grasses and cereals) was the only family with unlignified cell walls containing (1→3,1→4)- β - d -glucans. Moreover, the unlignified cell walls of the Poaceae contain a smaller proportion of pectic rhamnogalacturonans than those of the other Group A families. However, these studies did not include other families in the order Poales. We examined the polysaccharide compositions of unlignified cell walls from species of six Poales families: Anarthriaceae, Centrolepidaceae, Ecdeiocoleaceae, Flagellariaceae, Poaceae, and Restionaceae. The cell walls of all the species examined contained (1→3,1→4)- β -glucans with the exception of two Restionaceae species; these cell walls also contained similar, small proportions of pectic rhamnogalacturonans. Glucuronoarabinoxylans were a major component of these cell walls and smaller amounts of xyloglucans and glucomannans or galactoglucomannans were also present. We found the polysaccharide compositions of the lignified cell walls were similar and differed in similar ways from the polysaccharide compositions of unlignified cell walls from the same species. Our results are discussed in relation to the possible evolution of Poales families.