Age Effects on Hypocotyl Mechanics.

Numerous studies deal with composition and molecular processes involved in primary cell wall formation and alteration in Arabidopsis. However, it still remains difficult to assess the relation between physiological properties and mechanical function at the cell wall level. The thin and fragile structure of primary cell walls and their large biological variability, partly related to structural changes during growth, make mechanical experiments challenging.

Cooperative behavior of a sacrificial bond network and elastic framework in providing self-healing capacity in mussel byssal threads.

The dissipative and self-healing properties of mussel byssal threads are critical for their function as anchoring fibers in wave-battered habitats and central to their emergence as an exciting model system for bio-inspired polymers. Much is now understood about the structure-function relationships defining this remarkable proteinaceous bio-fiber; however, the molecular mechanisms underlying the distinctive tough, viscoelastic and self-healing behavior are still unclear. Here, we investigate elastic and dissipative contributions from the primary load-bearing proteins in the distal region of byssal threads (the preCols) using X-ray diffraction (XRD) combined with in situ tensile testing.

Role of Sacrificial Protein-Metal Bond Exchange in Mussel Byssal Thread Self-Healing.

Marine mussels tether to seashore surfaces with byssal threads, proteinaceous fibers that effectively dissipate energy from crashing waves. Protein-metal coordination bonds have been proposed to contribute to the characteristic mechanical and self-healing properties of byssal threads; however, very little is understood about how these cross-links function at the molecular level. In the present study, combined Raman and X-ray absorption spectroscopy (XAS) measurements were employed to confirm the presence of protein-Zn(2+) coordination bonds in the mussel byssus and to monitor transitions in the coordination structure during thread deformation and self-healing.

Metal-mediated molecular self-healing in histidine-rich mussel peptides.

Mussels withstand high-energy wave impacts in rocky seashore habitats by fastening tightly to surfaces with tough and self-healing proteinaceous fibers called byssal threads. Thread mechanical behavior is believed to arise from reversibly breakable metal coordination cross-links embedded in histidine-rich protein domains (HRDs) in the principle load-bearing proteins comprising the fibrous thread core. In order to investigate HRD behavior at the molecular level, we have synthesized a histidine-rich peptide derived from mussel proteins (His5-bys) and studied its reversible adhesive self-interaction in the presence and absence of metal ions using PEG-based soft-colloidal probes (SCPs).

Pectin may hinder the unfolding of xyloglucan chains during cell deformation: implications of the mechanical performance of Arabidopsis hypocotyls with pectin alterations.

Plant cell walls, like a multitude of other biological materials, are natural fiber-reinforced composite materials. Their mechanical properties are highly dependent on the interplay of the stiff fibrous phase and the soft matrix phase and on the matrix deformation itself. Using specific Arabidopsis thaliana mutants, we studied the mechanical role of the matrix assembly in primary cell walls of hypocotyls with altered xyloglucan and pectin composition.

Disrupting two Arabidopsis thaliana xylosyltransferase genes results in plants deficient in xyloglucan, a major primary cell wall component.

Xyloglucans are the main hemicellulosic polysaccharides found in the primary cell walls of dicots and nongraminaceous monocots, where they are thought to interact with cellulose to form a three-dimensional network that functions as the principal load-bearing structure of the primary cell wall. To determine whether two Arabidopsis thaliana genes that encode xylosyltransferases, XXT1 and XXT2, are involved in xyloglucan biosynthesis in vivo and to determine how the plant cell wall is affected by the lack of expression of XXT1, XXT2, or both, we isolated and characterized xxt1 and xxt2 single and xxt1 xxt2 double T-DNA insertion mutants. Although the xxt1 and xxt2 mutants did not have a gross morphological phenotype, they did have a slight decrease in xyloglucan content and showed slightly altered distribution patterns for xyloglucan epitopes.

In situ investigation of complex BaSO4 fiber generation in the presence of sodium polyacrylate. 2. Crystallization mechanisms.

The formation mechanisms of complex BaSO(4) fiber bundles and cones in the presence of polyacrylate sodium salt via a bioinspired approach at ambient temperature in an aqueous environment are reported. These complex organic-inorganic hybrid structures assemble after heterogeneous nucleation of amorphous precursor particle aggregates on polar surfaces, and the crystallization area can be patterned. In contrast to earlier reports, three different mechanisms based on the oriented attachment of nanoparticles were revealed for the formation of typical fibrous superstructures depending on the supersaturation or on the number of precursor particles.

Molecular changes during tensile deformation of single wood fibers followed by Raman microscopy.

Raman spectra were acquired in situ during tensile straining of mechanically isolated fibers of spruce latewood. Stress-strain curves were evaluated along with band positions and intensities to monitor molecular changes due to deformation. Strong correlations (r = 0.