Feruloylated polysaccharides in the primary cell walls of Festuca arundinacea

• Main Author: Wende, Gundolf
• Published: University of Edinburgh 1995
• Subjects: 572.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663650

Hydroxycinnamic acids are present in land plants as soluble and as insoluble (cell wall bound) esters. The most common hydroxycinnamic acids found in cell walls are ferulic and <I>p-</I>coumaric acids. These compounds are present particularly in Gramineae, where they are linked to arabinoxylan. The roles of cell wall bound ferulic acid have not been completely elucidated. Recently it has been reported that feruloylated arabinoxylans of cultured <I>Festuca </I>cells are relatively resistant to the enzyme mixture Driselase whereas Driselase can act successfully on other graminaceous cell walls (e.g. maize and barley) to release feruloylated oligosaccharides (e.g. ˜ 79% was solubilised from maize) such as Fer-Ara-Xyl (FAX) and Fer-Ara-Xyl<SUB>2</SUB> (FAXX). The resistance of <I>Festuca </I>feruloyl-arabinoxylans to Driselase means that only a very low percentage of the feruloyl groups were released as FAX and FAXX. The feruloylated material was solubilised by Driselase (˜80% as well) but in the form of relatively high molecular weight conjugates. The question of why <I>Festuca </I>feruloyl-arabinoxylan cannot be digested by Driselase to fragments such as FAX and FAXX to any great extent has now been investigated. The major feruloylated oligosaccharide (compound B) released from <I>Festuca arundinacea </I>cell walls by mild acid hydrolysis showed the unusual structure <I>5-O-(E)</I>-feruloyl-[<I>O-β</I>-D-xylopyranosyl-(1→)2]-L-arabinose. The (1→2)- linkage was established by NaIO<SUB>4</SUB>-oxidation and by PE of the NaBH<SUB>4</SUB>-reduced compound in molybdate-buffer alongside marker sugars with (1→2)- and (1→3)-linkages; the (<I>E</I>)-feruloyl ester group by its characteristic fluorescence and UV absorption; the <I>5-0</I>-linkage by partial hydrolysis of compound B to the known compound, 5-<I>O</I>-feruloyl-L-arabinose (compound A); and the β-linkage by hydrolysis with β-xylosidase. The structure was confirmed by NMR spectroscopy and methylation analysis.