Studies on the cell wall compositions of families in the commelinid monocotyledons

Abstract

The commelinid monocotyledons consist of four well-established orders, the Poales, Zingiberales, Commelinales and Arecales. The previously un-placed family, Dasypogonaceae, is now placed in a separate order, the Dasypogonales, sister to the Arecales. The commelinid monocotyledons are distinguished from other monocotyledons by the presence of ferulate in their non-lignified primary (NLP) cell walls. Both NLP and lignified secondary (LS) wall preparations were obtained from species in the families from each of the four well-established orders and their polysaccharide, phenolic acid and lignin compositions compared. Heteroxylans likely to be glucuronoarabinoxylans (GAXs) were the major non-cellulosic polysaccharides in the NLP wall preparations from each species examined, with the exception of that obtained from Phoenix canariensis (Arecaceae; Arecales), which had a lower proportion of heteroxylans and a higher proportion of pectic polysaccharides. A linkage analysis indicated that the preparations from species in families in the Zingiberales have larger proportions of GAXs than those from the Commelinales. However, the GAXs in the walls of the preparations from the Zingiberales species may be less substituted with arabinose and -D-GlcA than those from the Commelinales species. The LS wall preparations from species in all the families examined had higher proportions of heteroxylans compared with the corresponding NLP wall preparations. Furthermore, the arabinose to xylose ratios and the signals from glycosyl residues in the 2D-NMR spectra of the wall preparations indicated that in the LS wall preparations the GAXs were less substituted with arabinose than the GAXs in the NLP wall preparations. In the NLP wall preparations, high concentrations of ferulic and lower concentrations of p-coumaric acids were released by saponification, whereas in the LS wall preparations high concentrations of p-coumaric and lower concentrations of ferulic acid were released. In the 2D-NMR spectra of the purest NLP wall preparations, p-coumarate was present but S- and G-lignin units were not detected. This indicated that as found in the Poaceae, p-coumaric acid is esterified to GAXs in the walls of other families. It is likely that p-coumaric acid is esterified to GAXs in the LS walls and is also esterified to lignin units; however it is mainly accumulated in conjunction with lignification. In the LS wall preparations, the lignins were highly acylated with p-coumarate, which was largely esterified to the γ-OH of S-units and some G-units. In the LS wall preparations from Phoenix canariensis, I also found large concentrations of p-hydroxybenzoate. This indicated that the lignins in the walls of the Arecaceae may be unique as they are potentially acylated with both p-coumarate and p-hydroxybenzoate.