Extracellular cross-linking of xylan and xyloglucan in maize cell-suspension cultures: the role of oxidative phenolic coupling

Abstract

Cell-suspension cultures of maize ( Zea mays L.) released soluble extracellular polysaccharides (SEPs) into their medium. Some or all of the SEPs had feruloyl ester groups. Pulse-labelling with [(3)H]arabinose was used to monitor changes in the SEPs' M(r) (estimated by gel-permeation chromatography) with time after synthesis. Newly released (3)H-SEPs were 1.3-1.6 MDa, but between 2 days and 3 days after radiolabelling (in one experiment) or between 5 days and 6 days (in another), the (3)H-SEPs abruptly increased to approximately 17 MDa, indicating extensive cross-linking. The cross-linking involved both [(3)H]xylan and [(3)H]xyloglucan components of the SEPs. The cross-links could be cleaved by alkali, returning the SEPs to their original M(r). In 0.1 M NaOH at 37 degrees C, 58% cleavage was effected within 24 h. The requirement for such prolonged alkali treatment indicates that ester-bonded (e.g. diferuloyl) groups were not solely responsible for the cross-linking. Bonds cleaved only by relatively severe alkali could include benzyl ether linkages formed between sugar residues and oxidised phenolics that had quinone methide structures. The ability of alkali to cleave the cross-links was independent of the age of the (3)H-SEP molecules. Cross-linking of (3)H-SEPs in vivo was delayed (up to approx. 7 days after radiolabelling) by exogenous sinapic acid, chlorogenic acid or rutin-agents predicted to compete with the oxidative coupling of feruloyl-polysaccharides. The cross-linking was promoted by exogenous ferulic acid or l-tyrosine, possibly because these compounds acted as precursors for polysaccharide feruloylation, thus providing additional partner substrates for the oxidative coupling of previously formed (3)H-SEPs. The ability of certain phenolics to prevent the cross-linking of (3)H-SEPs supports the idea that the cross-linking involved phenolic oxidation.

Ca2+ Regulates Reactive Oxygen Species Production and pH during Mechanosensing inArabidopsisRoots

“…While long-term effects likely include regulation of gene expression (Apel and Hirt, 2004), rapid ROS production to the apoplast should rigidify and strengthen the cell wall through oxidative cross-linking of cell wall components (Campbell and Sederoff, 1996;Brady and Fry, 1997;Kerr and Fry, 2004). Such a role in enhancing cell wall stability is supported by the observation that defects in ROS production lead to bursting of growing root hairs, as does scavenging of extracellular ROS.…”

A Genomics Approach to Deciphering Lignin Biosynthesis in Switchgrass

“…Therefore, we have used both the cell suspension system and the stem internode section system to make predictions. Maize cell culture systems have been used previously to study cell wall cross-linking through ferulic acid or p-coumaric acids (Grabber et al, 1995;Fry et al, 2000;Kerr and Fry, 2004;Grabber et al, 2009), and it will be interesting to pursue such features of cell wall biosynthesis in the switchgrass cell culture system. (A, C, E) Transcript levels of the target genes in the C4H1-, CCR1-, and CCoAOMT-RNAi lines.…”

Progressive Inhibition by Water Deficit of Cell Wall Extensibility and Growth along the Elongation Zone of Maize Roots Is Related to Increased Lignin Metabolism and Progressive Stelar Accumulation of Wall Phenolics

“…Even if stress-induced increases in levels of phenolic dimers and trimers could be ascertained, it would still be necessary to show that they actually cross-linked the load-bearing polymers in the expanding walls. For example, it has been noted that ferulic acid trimers might also take the form of intrapolymer loops, and these would be unlikely to affect wall extensibility (Kerr and Fry, 2004).…”