Ultrastructure and Topochemistry of Plant Cell Wall by Transmission Electron Microscopy

Abstract

Plant cell walls are typically described as complex macromolecular composites consisting of an ordered array of cellulose microfibrils embedded in a matrix of noncellulosic polysaccharides and lignin. Generally, the plant cell wall can be divided into three major layers: middle lamella, primary cell wall, and secondary cell wall. Investigation of plant cell walls is complicated by the heterogeneous and complex hierarchical structure, as well as variable chemical composition between different sublayers. Thus, a complete understanding of the ultrastructure of plant cell walls is necessary. Transmission electron microscopy (TEM) has proven to be a powerful tool in elucidating fine details of plant cell walls at nanoscale. The present chapter describes the layering structure and topochemistry of plant cell wall revealed by TEM.

Cell wall microstructure, pore size distribution and absolute density of hemp shiv

“…The dark staining of the middle lamella indicates that it is strongly lignified. Previous reports suggest that the secondary wall of hardwood consists of an outer layer (S1), a middle layer (S2) and an inner layer (S3) [ 12 , 27 ]. These could not be distinguished by CM because of the similarity in their chemical composition and the low resolution of CM.…”

Fluorescent Nano-Probes to Image Plant Cell Walls by Super-Resolution STED Microscopy

“…Both confocal and STED profiles seem noisy with no clear trend. In contrast, the STED-deconvolved image shows a well-defined profile corresponding to the CC architecture: two maximum intensity peaks corresponding to the ML of two adjacent cells and a minor peak in between, probably revealing the heterogeneity of lignin distribution in the CC structure, in accordance with the architecture imaged by transmission electron microscopy [ 24 , 25 ]. Interestingly, the use of fluorescent probes like PEG-R, which interacts with lignin, gives a chemical mapping of lignin distribution in the cell wall, revealing a high lignin density in CCs and to a lesser extent in the primary and secondary cell walls, in accordance, for example, with chemical imaging realized by confocal Raman microscopy [ 26 ].…”

“…Interestingly, the use of fluorescent probes like PEG-R, which interacts with lignin, gives a chemical mapping of lignin distribution in the cell wall, revealing a high lignin density in CCs and to a lesser extent in the primary and secondary cell walls, in accordance, for example, with chemical imaging realized by confocal Raman microscopy [ 26 ]. Overall, although it does not reach the high resolution of electron microscopy [ 24 ], STED microscopy and in particular the deconvolution process provide images with largely reduced signal-to-noise ratios, and allows the easier identification of plant cell wall fine structures.…”

“…Interestingly, the STED technique provides a gain in image resolution when used in combination with deconvolution treatment. Even if the STED contrast and resolution cannot reach those of transmission electron microscopy [ 24 ], STED benefits from the simplicity of sample preparation since even relatively thick specimens (several tens of µm) can be observed, contrary to transmission electron microscopy, which requires ultra-thin samples (10–100 nm thickness) [ 24 ]. Moreover, STED microscopy is versatile since different types of chemical features can be observed depending on the type of extrinsic fluorescent probes that are used for imaging.…”

Formation of a subero-lignified apical deposit in root tip of radish (Raphanus sativus) as a response to copper stress

“…Lignin deposition stiffens the cell wall and make it impermeable, but it is often associated with cell death (Voxeur et al, 2015). During development of tissues, lignification is regarded as a final step in cell differentiation (Zhou et al, 2015) and, like suberization, developmentally determined lignification can be enhanced by stress-induced lignification of disturbed tissues (Caño-Delgado et al, 2003;Voxeur et al, 2015). A shift in the normal development of xylem lignification to early deposition of phenolics into metaxylem vessels occurs in the elongation zone of maize roots subjected to water deficit.…”