The polysaccharide composition of Poales cell walls: Poaceae cell walls are not unique

Monocotyledon families can be divided into two groups depending on the pres ence (Group A) or absence (Group B) of ferulic acid ester-linked to their u nlignified cell walls. The two groups also differ in the major types of non -cellulosic polysaccharides in their unlignified cell walls: in Group A the y are glucuronoarabinoxylans (GAXs), and in Group B they are pectic polysac charides. Previous studies suggested that among the Group A families, the P oaceae (grasses and cereals) was the only family with unlignified cell wall s containing (1 --> 3,1 --> 4)-beta-D-glucans. Moreover, the unlignified ce ll walls of the Poaceae contain a smaller proportion of pectic rhamnogalact uronans than those of the other Group A families. However, these studies di d not include other families in the order Poales. We examined the polysacch aride compositions of unlignified cell walls from species of six Poales fam ilies: Anarthriaceae, Centrolepidaceae, Ecdeiocoleaceae, Flagellariaceae, P oaceae, and Restionaceae. The cell walls of all the species examined contai ned (1 --> 3,1 --> 4)-beta-glucans with the exception of two Restionaceae s pecies; these cell walls also contained similar, small proportions of pecti c rhamnogalacturonans. Glucuronoarabinoxylans were a major component of the se cell walls and smaller amounts of xyloglucans and glucomannans or galact oglucomannans were also present. We found the polysaccharide compositions o f the lignified cell walls were similar and differed in similar ways from t he polysaccharide compositions of unlignified cell walls from the same spec ies. Our results are discussed in relation to the possible evolution of Poa les families. (C) 1998 Elsevier Science Ltd. All rights reserved.