The distribution of ester-linked ferulic acid in the cell walls of angiosperms

Ester-linked ferulic acid occurs in the cell walls of two major groups of angiosperms, the commelinid monocotyledons and the 'core' Caryophyllales, at concentrations > 3.5 mg g(-1) cell walls, and has been detected in primary cell walls by its autofluorescence using ultraviolet fluorescence microscopy. Both of these groups are resolved as monophyletic clades in phylogenetic trees constructed using gene sequences. In the primary cell walls of the commelinid monocotyledons, including the grasses (family Poaceae), the ferulic acid is ester-linked to the non-cellulosic polysaccharide glucuronoarabinoxylan. In contrast, in the 'core' Caryophyllales, the ferulic acid is ester-linked to the side chain arabinans and galactans of the pectic polysaccharide rhamnogalacturonan-1, at least in the family Amaranthaceae. In the walls of both angiosperm groups, a range of dehydrodiferulates have also been found. These are formed oxidatively via radical coupling and result in the cross linking of the polysaccharides to which they are attached. Much lower concentrations of ester-linked ferulic acid have been found in cell walls isolated from other angiosperms, although physiological stress conditions may cause increases in these concentrations. The polysaccharides to which the ferulic acid is attached to in the cell walls of these other angiosperms is unknown.