The Wood Cell Wall at the Ultrastructural Scale - Formation and Topochemical Organization

Abstract

The macromolecular organization of the secondary wall of the cells from tree xylem is in large part responsible for the mechanical and physiological properties of wood. Modeling secondary walls of wood is difficult because information about their macromolecular architecture at the ultrastructural scale is missing. Numerous microscopic studies have provided views of the lignocellulosic composite material, but nanoscale distribution of the polymers and their interaction in muro is still not clearly understood. The intimate macromolecular organization of cell walls is defined during their differentiation. It is at the stage of wall thickening corresponding to secondary wall development that the topochemical organization and the interactions between cellulose, hemicelluloses and lignin are established.Using the conjunction of the high resolution of transmission electron microscopy (TEM) and the specificity of immunological probes directed against the main cell wall polymers, we investigated the deposition of hemicelluloses and lignins from the early stage of cambium differentiation to the mature fiber and vessel walls in growing model plants of Arabidopsis thaliana and poplar. TEM examination of differentiating cells as well as various wood and wood -derived materials and genetic plant mutants brought multiple evidence of the lamellar sub-organization of the secondary walls. Immuno-gold labeling showed that two structurally different xylan types were deposited at different stages in the wall thickening. Similarly two different types of lignin molecules were shown to be differentially polymerized at different steps of the building of the wall, lignin molecules of the condensed type being first deposited at the earliest stage of secondary thickening before the non-condensed types. This process may be modified in response to environmental factors, as in tension wood.The spatio-temporal relationships occurring between hemicelluloses, lignin and cellulose microfibrils (CMFs) during the secondary wall development suggest that xylans with less substituted chains would be more directly interacting with CMFs than those with higher substitution patterns. It also suggests that lignin molecules of the non-condensed type have a function in bringing cohesion between the lamellae of CMFs. A model of wall assembly during secondary thickening is proposed.

Temporal Alterations in the Secretome of the Selective Ligninolytic Fungus Ceriporiopsis subvermispora during Growth on Aspen Wood Reveal This Organism's Strategy for Degrading Lignocellulose

“…This sequential enzyme secretion may be in response to the challenging ultrastructure of plant cell walls, in which cellulose fibrils are surrounded by hemicellulose and lignin (48). Further support of this view will require biochemical analyses of specific enzymes (e.g., Araf) as well as microscopic localization of the enzymes in relation to cell wall decay over time.…”

Impact of Lignin and Carbohydrate Chemical Structures on Degradation Reactions during Hardwood Kraft Pulping Processes

“…Hemicelluloses in the matrix have been reported to be associated with condensed type lignin and in a more advanced stage of cell wall growth, to non-condensed lignin moieties also. This association is believed to be an indication of lignin-carbohydrate complex formation in which lignin-to-hemicellulose bonds establish an essential element of secondary cell wall formation (Ruel et al 2006). …”

Quantitative Evaluation of Hybrid Aspen Xylem and Immunolabeling Patterns Using Image Analysis and Multivariate Statistics

“…It has been used extensively over the last decade to study the development and topochemistry of primary and secondary cell walls in plant and xylem tissues, including in genetically modified trees (e.g. Awano et al 2000;Willats et al 2000;Grunwald et al 2001Grunwald et al , 2002aZhang et al 2003;Joseleau et al 2004;Knox et al 2005;Hosoo et al 2006;Ruel et al 2006;Altaner et al 2007a, b;Daniel et al 2006;Nishikubo et al 2007;Bowling and Vaughn 2008;Mast et al 2009;Sandquist et al 2010;Kim and Daniel 2013). It is an outstanding observational aid to highlight the presence and availability of epitopes, within limits of the specificity determined for each antibody.…”