Advances in determination of polymer structure and in preservation of structure for electron microscopy provide the best view to date of how polysaccharides and structural proteins are organized into plant cell walls. The walls that form and partition dividing cells are modified chemically and structurally from the walls expanding to provide a cell with its functional form. In grasses, the chemical structure of the wall differs from that of all other flowering plant species that have been examined. Nevertheless, both types of wall must conform to the same physical laws. Cell expansion occurs via strictly regulated reorientation of each of the wall's components that first permits the wall to stretch in specific directions and then lock into final shape. This review integrates information on the chemical structure of individual polymers with data obtained from new techniques used to probe the arrangement of the polymers within the walls of individual cells. We provide structural models of two distinct types of walls in flowering plants consistent with the physical properties of the wall and its components.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.1993.tb00007.x

Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth

Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.

/pdf/growth-of-the-plant-cell-wall-4k81okl2ih.pdf

Growth of the plant cell wall

Gene families are growing rapidly, but standard methods for inferring phylogenies do not scale to alignments with over 10,000 sequences. We present FastTree, a method for constructing large phylogenies and for estimating their reliability. Instead of storing a distance matrix, FastTree stores sequence profiles of internal nodes in the tree. FastTree uses these profiles to implement neighbor-joining and uses heuristics to quickly identify candidate joins. FastTree then uses nearest-neighbor interchanges to reduce the length of the tree. For an alignment with N sequences, L sites, and a different characters, a distance matrix requires O(N^2) space and O(N^2 L) time, but FastTree requires just O( NLa + N sqrt(N) ) memory and O( N sqrt(N) log(N) L a ) time. To estimate the tree's reliability, FastTree uses local bootstrapping, which gives another 100-fold speedup over a distance matrix. For example, FastTree computed a tree and support values for 158,022 distinct 16S ribosomal RNAs in 17 hours and 2.4 gigabytes of memory. Just computing pairwise Jukes-Cantor distances and storing them, without inferring a tree or bootstrapping, would require 17 hours and 50 gigabytes of memory. In simulations, FastTree was slightly more accurate than neighbor joining, BIONJ, or FastME; on genuine alignments, FastTree's topologies had higher likelihoods. FastTree is available at http://microbesonline.org/fasttree.

/pdf/fast-tree-computing-large-minimum-evolution-trees-with-4grq0gwfpy.pdf

Fast Tree: Computing Large Minimum-Evolution Trees with Profiles instead of a Distance Matrix

Pectin structure and biosynthesis

Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

Enzymatic Synthesis and Purification of [3H]Uridine Diphosphate Galacturonic Acid for Use in Studying Golgi-Localized Transporters

Visualizing pectin polymer-polymer entanglement produced by interfacial water movement.

Plants are aggressive in their development. They can overcome severe injuries, such as removal of a limb or decapitation, by forming new centers of cell division called meristems that develop into roots, vegetative shoots or flowers. A major, albeit elusive, goal in plant developmental biology is to understand the molecular basis for the plasticity that allows differentiated cells to embark upon new developmental programs.

Novel Experimental Systems for Determining Cellular Competence and Determination

The discoveries that complex carbohydrates are tissue-specific cell-surface antigens and the receptors for hormones, toxins, bacteria, and viruses have created considerable interest in complex carbohydrates. Furthermore, the complex carbohydrate portions of some glycoprotein hormones are required for their biological activity, and the complex carbohydrates of some glycoprotein enzymes keep the enzymes stable, while the carbohydrates of some glycoproteins direct the glycoproteins to their proper locations. Moreover, the immune response to glycoproteins is often directed to their carbohydrate side chains, and the carbohydrate chains have been shown to affect the activity and residence time of glycoprotein pharmaceuticals. Still another discovery that has generated considerable interest in complex carbohydrate research is that these molecules perform regulatory functions in plants and animals, often at the level of controlling gene expression.

Oligosaccharins ― Plant regulatory molecules

Pectin binds the mesothelial glycocalyx of visceral organs, suggesting its potential role as a mesothelial sealant. To assess the mechanical properties of pectin films, we compared pectin films with a less than 50% degree of methyl esterification (low-methoxyl pectin, LMP) to films with greater than 50% methyl esterification (high-methoxyl pectin, HMP). LMP and HMP polymers were prepared by step-wise dissolution and high-shear mixing. Both LMP and HMP films demonstrated a comparable clear appearance. Fracture mechanics demonstrated that the LMP films had a lower burst strength than HMP films at a variety of calcium concentrations and hydration states. The water content also influenced the extensibility of the LMP films with increased extensibility (probe distance) with an increasing water content. Similar to the burst strength, the extensibility of the LMP films was less than that of HMP films. Flexural properties, demonstrated with the 3-point bend test, showed that the force required to displace the LMP films increased with an increased calcium concentration (p < 0.01). Toughness, here reflecting deformability (ductility), was variable, but increased with an increased calcium concentration. Similarly, titrations of calcium concentrations demonstrated LMP films with a decreased cohesive strength and increased stiffness. We conclude that LMP films, particularly with the addition of calcium up to 10 mM concentrations, demonstrate lower strength and toughness than comparable HMP films. These physical properties suggest that HMP has superior physical properties to LMP for selected biomedical applications.

https://www.mdpi.com/1420-3049/25/1/75/pdf

Debra Mohnen

Papers

Enzymatic Synthesis and Purification of [3H]Uridine Diphosphate Galacturonic Acid for Use in Studying Golgi-Localized Transporters

Visualizing pectin polymer-polymer entanglement produced by interfacial water movement.

Novel Experimental Systems for Determining Cellular Competence and Determination

Oligosaccharins ― Plant regulatory molecules

The Effect of Calcium on the Cohesive Strength and Flexural Properties of Low-Methoxyl Pectin Biopolymers.