Cell Wall Mechanics Research Articles

Analysis of Cell Wall Mechanics in Fission Yeast.

The growth and shape of fungal cells, such as fission yeast, are strongly constrained by the mechanics of their cell wall (CW). The cell wall encases the plasma membrane and defines instantaneous cell shapes by opposing turgor pressure-derived stress on the cell surface. Measuring cell wall mechanical properties may thus bring key insights into the regulation of cell morphogenesis, cell growth, but also cell surface integrity and survival. The fission yeast cell wall has a thickness of a few tens to hundreds of nanometers, and bulk elasticity similar to that of rubber (tens of MPa). These mechanical properties vary locally around single cells, for instance, at the new vs. old growing ends, or birth scars, and may also largely depend on growth conditions and life cycle phases. While cell wall thickness and mechanics have been traditionally measured by complex methodologies including electron microscopy and atomic force microscopy, we here propose a method based on light microscopy to infer with medium-throughput cell wall mechanical properties, as well as turgor pressure in time and space in living cells. This analysis will enhance our appreciation of the mechanical regulation of fission yeast cell morphogenesis and may be directly transferable to the study of other fungal cells.

EFFECT OF PHENOL FORMALDEHYDE RESIN IMPREGNATION ON NANODYNAMIC VISCOELASTICITY OF PINUS MASSONIANA LAMB IN WET STATE

We evaluated the effects of phenol formaldehyde (PF) resin modification on Masson pine (Pinus massoniana Lamb.) wood cell wall in wet states. The penetration degree of PF resin into wood cell was determined using confocal laser scanning microscopy (CLSM). The micromechanical properties of PF-modified wood cell walls in wet state were analyzed by quasi-static nanoindentation and dynamic modulus mapping techniques. Results showed that the PF resin significantly affected the static viscoelasticity and nanodynamic viscoelasticity of wood cell walls in oven-dried and wet states. The cell-wall mechanics increased at a PF resin concentration due to the increased bulking effects, such as decreased crystallinity of cellulose. Furthermore, the microfibrillar angle (MFA) of cell walls was lower than that of the control wood cell wall. The cell-wall mechanics of PF resin-modified sample decreased small than control sample in wet states.

Antifungal Mechanism of Natural Products Derived from Plants: A Review

Fungal resistance to the limited existing antifungal agents has become a considerable public health problem in the past few decades. However, natural products with multiple bioactivities are important sources for developing new therapeutic agents against fungi. Consequently, there is an urgent need to grasp the antifungal mechanism of natural products. In this review, the primary antifungal mechanisms of natural products derived from plants, including targeting the cell wall, cell membrane, mitochondria, biofilm and other mechanisms, are elaborated. This article critically describes the compounds with high antifungal activity, revealing opportunities for future research such as clinical trials or utilization as environmental disinfectants.

Architecture and functions of stomatal cell walls in eudicots and grasses.

Like all plant cells, the guard cells of stomatal complexes are encased in cell walls that are composed of diverse, interacting networks of polysaccharide polymers. The properties of these cell walls underpin the dynamic deformations that occur in guard cells as they expand and contract to drive the opening and closing of the stomatal pore, the regulation of which is crucial for photosynthesis and water transport in plants. Our understanding of how cell wall mechanics are influenced by the nanoscale assembly of cell wall polymers in guard cell walls, how this architecture changes over stomatal development, maturation and ageing and how the cell walls of stomatal guard cells might be tuned to optimize stomatal responses to dynamic environmental stimuli is still in its infancy. In this review, we discuss advances in our ability to probe experimentally and to model the structure and dynamics of guard cell walls quantitatively across a range of plant species, highlighting new ideas and exciting opportunities for further research into these actively moving plant cells.

Xyloglucan deficiency leads to a reduction in turgor pressure and changes in cell wall properties, affecting early seedling establishment

Xyloglucan is believed to play a significant role in cell wall mechanics of dicot plants. Surprisingly, Arabidopsis plants defective in xyloglucan biosynthesis exhibit nearly normal growth and development. We investigated a mutant line, cslc-Δ5, lacking activity in all five Arabidopsis cellulose synthase like-C (CSLC) genes responsible for xyloglucan backbone biosynthesis. We observed that this xyloglucan-deficient line exhibited reduced cellulose crystallinity and increased pectin levels, suggesting the existence of feedback mechanisms that regulate wall composition to compensate for the absence of xyloglucan. These alterations in cell wall composition in the xyloglucan-absent plants were further linked to a decrease in cell wall elastic modulus and rupture stress, as observed through atomic force microscopy (AFM) and extensometer-based techniques. This raised questions about how plants with such modified cell wall properties can maintain normal growth. Our investigation revealed two key factors contributing to this phenomenon. First, measurements of turgor pressure, a primary driver of plant growth, revealed that cslc-Δ5 plants have reduced turgor, preventing the compromised walls from bursting while still allowing growth to occur. Second, we discovered the conservation of elastic asymmetry (ratio of axial to transverse wall elasticity) in the mutant, suggesting an additional mechanism contributing to the maintenance of normal growth. This novel feedback mechanism between cell wall composition and mechanical properties, coupled with turgor pressure regulation, plays a central role in the control of plant growth and is critical for seedling establishment in a mechanically challenging environment by affecting shoot emergence and root penetration.

Lytic Activity Spectra of Bacteriophages

One of the central topics in bacteriophage research is the host specificity. It depends on the success of completing viral life cycle stages, including adsorption, penetration of the genetic material of the virus into the cell and its replication, assembly of phage particles and cell lysis. Laboratory assessments of the spectrum of lytic activity of phages are inextricably linked to significant methodological biases, and the often used spot test method can be associated with a large percentage of false-positive results. Along with the variety of types of phage specificity, there is temporal variability. The co-evolution of phages and bacteria leads to the acquisition of resistance to viruses by bacteria and the accumulation of mutations in the genomes of bacteriophages aimed at overcoming this resistance. At the same time, the adaptation of bacteriophages to bacteria that are evolutionarily distant from the isolation hosts is barely possible. This barrier is based on the peculiarities of metabolism, cell wall structures and mechanisms for the implementation of matrix processes. The spatial factor of phage specificity is manifested in the greater breadth of the spectra of lytic activity of bacteriophages on local samples of bacteria compared to the spectra assessed on samples of isolates from habitats geographically distant from the place of virus isolation.

A self-regulatory cell-wall-sensing module at cell edges controls plant growth.

Morphogenesis of multicellular organs requires coordination of cellular growth. In plants, cell growth is determined by turgor pressure and the mechanical properties of the cell wall, which also glues cells together. Because plants have to integrate tissue-scale mechanical stresses arising through growth in a fixed tissue topology, they need to monitor cell wall mechanical status and adapt growth accordingly. Molecular factors have been identified, but whether cell geometry contributes to wall sensing is unknown. Here we propose that plant cell edges act as cell-wall-sensing domains during growth. We describe two Receptor-Like Proteins, RLP4 and RLP4-L1, which occupy a unique polarity domain at cell edges established through a targeted secretory transport pathway. We show that RLP4s associate with the cell wall at edges via their extracellular domain, respond to changes in cell wall mechanics and contribute to directional growth control in Arabidopsis.

Dynamic Structural Change of Plant Epidermal Cell Walls under Strain.

The molecular foundations of epidermal cell wall mechanics are critical for understanding structure-function relationships of primary cell walls in plants and facilitating the design of bioinspired materials. To uncover the molecular mechanisms regulating the high extensibility and strength of the cell wall, the onion epidermal wall is stretched uniaxially to various strains and cell wall structures from mesoscale to atomic scale are characterized. Upon longitudinal stretching to high strain, epidermal walls contract in the transverse direction, resulting in a reduced area. Atomic force microscopy shows that cellulose microfibrils exhibit orientation-dependent rearrangements at high strains: longitudinal microfibrils are straightened out and become highly ordered, while transverse microfibrils curve and kink. Small-angle X-ray scattering detects a 7.4nm spacing aligned along the stretch direction at high strain, which is attributed to distances between individual cellulose microfibrils. Furthermore, wide-angle X-ray scattering reveals a widening of (004) lattice spacing and contraction of (200) lattice spacing in longitudinally aligned cellulose microfibrils at high strain, which implies longitudinal stretching of the cellulose crystal. These findings provide molecular insights into the ability of the wall to bear additional load after yielding: the aggregation of longitudinal microfibrils impedes sliding and enables further stretching of the cellulose to bear increased loads.

The nonlinear mechanics of highly extensible plant epidermal cell walls.

Plant epidermal cell walls maintain the mechanical integrity of plants and restrict organ growth. Mechanical analyses can give insights into wall structure and are inputs for mechanobiology models of plant growth. To better understand the intrinsic mechanics of epidermal cell walls and how they may accommodate large deformations during growth, we analyzed a geometrically simple material, onion epidermal strips consisting of only the outer (periclinal) cell wall, ~7 μm thick. With uniaxial stretching by >40%, the wall showed complex three-phase stress-strain responses while cyclic stretching revealed reversible and irreversible deformations and elastic hysteresis. Stretching at varying strain rates and temperatures indicated the wall behaved more like a network of flexible cellulose fibers capable of sliding than a viscoelastic composite with pectin viscosity. We developed an analytic framework to quantify nonlinear wall mechanics in terms of stiffness, deformation, and energy dissipation, finding that the wall stretches by combined elastic and plastic deformation without compromising its stiffness. We also analyzed mechanical changes in slightly dehydrated walls. Their extension became stiffer and more irreversible, highlighting the influence of water on cellulose stiffness and sliding. This study offers insights into the structure and deformation modes of primary cell walls and presents a framework that is also applicable to tissues and whole organs.

Antifungal activity of Annona crassiflora Mart. dichloromethane fraction against strains of C. albicans.

Products derived from medicinal plants with antimicrobial activity are considered a promising alternative in the treatment of fungal infections. In this perspective, this study proposed to evaluate the antifungal activity of the dichloromethane fraction of Annona crassiflora Mart. against C. albicans strains. Tests were carried out to determine Minimum Inhibitory Concentration (MIC), Minimum Fungicide Concentration (MFC), microbial growth kinetics, fungal cell wall and membrane mechanisms of action, antifungal biofilm activity, and cytotoxic effects on human erythrocytes. The extract presented MIC and MFC values that ranged from 256 µg/mL to 1,024 µg/mL, with fungicidal activity in the microbial growth kinetics assay. The mechanism of action did not occur through damage to the cell wall or via binding to ergosterol in the membrane, though the fraction presents activity against biofilm and is not cytotoxic in human erythrocytes. The dichloromethane fraction of Annona crassiflora Mart. presented antifungal activity and reduced biofilm growth, without toxicity against human erythrocytes; however, further studies are needed to define its mechanism of action.

Regiospecific Cellulose Orientation and Anisotropic Mechanical Property in Plant Cell Walls.

Cellulose microfibrils (CMFs) are a major load-bearing component in plant cell walls. Thus, their structures have been studied extensively with spectroscopic and microscopic characterization methods, but the findings from these two approaches were inconsistent, which hampers the mechanistic understanding of cell wall mechanics. Here, we report the regiospecific assembly of CMFs in the periclinal wall of plant epidermal cells. Using sum frequency generation spectroscopic imaging, we found that CMFs are highly aligned in the cell edge region where two cells form a junction, whereas they are mostly isotropic on average throughout the wall thickness in the flat face region of the epidermal cell. This subcellular-level heterogeneity in the CMF alignment provided a new perspective on tissue-level anisotropy in the tensile modulus of cell wall materials. This finding also has resolved a previous contradiction between the spectroscopic and microscopic imaging studies, which paves a foundation for better understanding of the cell wall architecture, especially structure-geometry relationships.

Antibacterial Effect of Black Ethanol Extract (Camellia sinensis) on The Growth of Porphyromonas gingivalis Bacteria

Background: Chronic periodontitis is one of the inflammatory diseases in the oral cavity that can cause damage to the structure of the supporting tissues of the teeth. The bacterium Porphyromonas gingivalis is the cause of chronic periodontitis which has specific virulence factors that produce lipopolysaccharides by destroying the host cell wall mechanism. Black tea with the Latin name Camellia sinensis contains theaflavins with antibacterial effects. Materials and methods: This study was an in vitro experimental laboratory study with disc diffusion method (Kirby Bauer), minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). The samples of this study were black tea ethanol extract with a concentration of 10%, 20%, 40%, 60%, 80%, and 100% with positive control group is chlorhexidine 0,2%, and negative control group is BHI broth, which tested Porphyromonas gingivalis. The Kruskal Wallis test results showed that there were statistically significant differences between the diameter of the bacterial inhibitory zone produced from the concentration group of black tea ethanol extract (7 mm), 40% (8,6 mm), 60% (10 mm), 80% (10,6 mm), and 100% (11,2 mm) (P <0.05). The Spearman correlation test results (r=0.431) showed a positive correlation with moderate strength between an increase in the concentration of black tea ethanol extract to the diameter of the bacterial inhibitory zone. Result: The MIC value in this study is 10% and the result of MBC is 20%. Conclusion: the ethanol extract of black tea has an antibacterial effect on Porphyromonas gingivalis. There is an increase in inhibition zone diameter along with an increase in the concentration of black tea extract, which indicates black tea ethanol extract has concentration-dependent antibacterial properties.

Brassinosteroid coordinates cell layer interactions in plants via cell wall and tissue mechanics.

Growth coordination between cell layers is essential for development of most multicellular organisms. Coordination may be mediated by molecular signaling and/or mechanical connectivity between cells, but how genes modify mechanical interactions between layers is unknown. Here we show that genes driving brassinosteroid synthesis promote growth of internal tissue, at least in part, by reducing mechanical epidermal constraint. We identified a brassinosteroid-deficient dwarf mutant in the aquatic plant Utricularia gibba with twisted internal tissue, likely caused by mechanical constraint from a slow-growing epidermis. We tested this hypothesis by showing that a brassinosteroid mutant in Arabidopsis enhances epidermal crack formation, indicative of increased tissue stress. We propose that by remodeling cell walls, brassinosteroids reduce epidermal constraint, showing how genes can control growth coordination between layers by means of mechanics.

Plant polygalacturonase structures specify enzyme dynamics and processivities to fine-tune cell wall pectins.

Polygalacturonases (PGs) fine-tune pectins to modulate cell wall chemistry and mechanics, impacting plant development. The large number of PGs encoded in plant genomes leads to questions on the diversity and specificity of distinct isozymes. Herein, we report the crystal structures of 2 Arabidopsis thaliana PGs, POLYGALACTURONASE LATERAL ROOT (PGLR), and ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE2 (ADPG2), which are coexpressed during root development. We first determined the amino acid variations and steric clashes that explain the absence of inhibition of the plant PGs by endogenous PG-inhibiting proteins (PGIPs). Although their beta helix folds are highly similar, PGLR and ADPG2 subsites in the substrate binding groove are occupied by divergent amino acids. By combining molecular dynamic simulations, analysis of enzyme kinetics, and hydrolysis products, we showed that these structural differences translated into distinct enzyme-substrate dynamics and enzyme processivities: ADPG2 showed greater substrate fluctuations with hydrolysis products, oligogalacturonides (OGs), with a degree of polymerization (DP) of ≤4, while the DP of OGs generated by PGLR was between 5 and 9. Using the Arabidopsis root as a developmental model, exogenous application of purified enzymes showed that the highly processive ADPG2 had major effects on both root cell elongation and cell adhesion. This work highlights the importance of PG processivity on pectin degradation regulating plant development.

Slits in the wall! Pulvinar slits confer unique cell wall mechanics for leaf movement.

Slits in the wall! Pulvinar slits confer unique cell wall mechanics for leaf movement.

DEFECTIVE KERNEL1 regulates cellulose synthesis and affects primary cell wall mechanics.

The cell wall is one of the defining features of plants, controlling cell shape, regulating growth dynamics and hydraulic conductivity, as well as mediating plants interactions with both the external and internal environments. Here we report that a putative mechanosensitive Cys-protease DEFECTIVE KERNEL1 (DEK1) influences the mechanical properties of primary cell walls and regulation of cellulose synthesis. Our results indicate that DEK1 is an important regulator of cellulose synthesis in epidermal tissue of Arabidopsis thaliana cotyledons during early post-embryonic development. DEK1 is involved in regulation of cellulose synthase complexes (CSCs) by modifying their biosynthetic properties, possibly through interactions with various cellulose synthase regulatory proteins. Mechanical properties of the primary cell wall are altered in DEK1 modulated lines with DEK1 affecting both cell wall stiffness and the thickness of the cellulose microfibril bundles in epidermal cell walls of cotyledons.

Role of cell wall anisotropy on guard cell mechanics in Arabidopsis thaliana.

The function of plant stomata is regulated by nanoscale cellular components and turgor pressure in flanking guard cells that control stomatal pore size to facilitate gas exchange and photosynthesis. Cell wall nanostructure plays a critical role in stomatal behavior. Stomatal aperture is regulated by tuning the mechanical properties of guard cell walls and by water uptake or release by the cells. However, the specific mechanical roles of different wall components, especially in newly maturing guard cells, are unclear. Here, we used a combination of molecular genetics, nanoindentation in normal and lateral directions, computational modeling, and microscopy to investigate the influences of wall components and maturation on wall mechanics and turgor pressure in stomatal guard cells. Lateral indentation measurements allow the unique anisotropic properties of each guard cell to be quantified with respect to age and genotype, including mutants with lower cellulose content and with lower or higher pectin molecular weight. Our results highlight the significance of cellulose in modulating the dynamics of guard cells by affecting wall anisotropy and emphasize the role of pectin modification for tuning stomatal responses to environmental stimuli. Our nanoindentation measurements when combined with finite element modeling allow the wall modulus, anisotropy, and turgor pressure to be measured. We also found that both cell wall mechanics and turgor pressure undergo significant changes during stomatal maturation. The role of cell wall architecture in determining anisotropic wall mechanics is also discussed. Together, these results provide new insights of wall mechanics and their effect on stomatal function and growth in plants.

Structure of fungal cell walls and remodeling by antifungal drugs elucidated using solid-state NMR.

Understanding the cell wall structure, dynamics, and mechanisms of adaptations are important for the development of cell wall-targeted drugs for the treatment of fatal infections caused by fungi. We first combined ssNMR, and functional genomics analysis to identify the functionality of cell wall carbohydrates in Aspergillus fumigatus and four mutants depleted of major structural polysaccharides. We revealed a rigid inner core of the cell wall formed by tightly associated chitin and α-1,3-glucan, which are embedded in a soft matrix of β-glucans and capped by a mobile outer shell rich in galactosaminogalactan and galactomannan. The distribution of α-1,3-glucan in chemically and dynamically distinct domains supports its dual functionality in structure and pathogenicity. Also, ssNMR revealed the modification of polymer dynamics which suggests that fungi produce a denser and hydrophobic cell wall as a response to structural defects. Second, we characterized the structural responses of A. fumigatus cell walls to the treatment of antifungal drugs. The drug-treated cell walls are highly hydrophobic and stiff to resist external stress. The fungi also increased the content of chitin and produced new forms of α-glucans to compensate for the loss of β-glucan due to drug inhibition. Third, we found that the crystalline structure of chitin bears intrinsic heterogeneity, which is resistant to caspofungin treatment. We documented the unique structural fingerprints of chitin across different fungal species. Finally, we used an innovative approach combing the ssNMR with the dynamic nuclear polarization technique to characterize the cell wall organization in different morphotypes varied along with the life cycle, revealing a highly conserved carbohydrate core in both conidia and mycelia. These studies and the biophysical techniques yield essential information that can serve as potential targets for discovering novel antifungal compounds with broad spectrums.

Polymer-Antimicrobial Peptide Constructs with Tailored Drug-Release Behavior

Microbial resistance is one of the main problems of modern medicine. Recently, antimicrobial peptides have been recognized as a novel approach to overcome the microbial resistance issue, nevertheless, their low stability, toxicity, and potential immunogenic response in biological systems have limited their clinical application. Herein, we present the design, synthesis, and preliminary biological evaluation of polymer-antibacterial peptide constructs. The antimicrobial GKWMKLLKKILK-NH2 oligopeptide (PEP) derived from halictine, honey bee venom, was bound to a polymer carrier via various biodegradable spacers employing the pH-sensitive or enzymatically-driven release and reactivation of the PEP's antimicrobial activity. The antibacterial properties of the polymer-PEP constructs were assessed by a determination of the minimum inhibitory concentrations, followed by fluorescence and transmission electron microscopy. The PEP exerted antibacterial activity against both, gram-positive and negative bacteria, via disruption of the bacterial cell wall mechanism. Importantly, PEP partly retained its antibacterial efficacy against Staphylococcus epidermidis, Escherichia coli, and Acinetobacter baumanii even though it was bound to the polymer carrier. Indeed, to observe antibacterial activity similar to the free PEP, the peptide has to be released from the polymer carrier in response to a pH decrease. Enzymatically-driven release and reactivation of the PEP antimicrobial activity were recognized as less effective when compared to the pH-sensitive release of PEP.

Revisiting the relationship between turgor pressure and plant cell growth.

Growth is central to plant morphogenesis. Plant cells are encased in rigid cell walls, and they must overcome physical confinement to grow to specific sizes and shapes. Cell wall tension and turgor pressure are the main mechanical components impacting plant cell growth. Cell wall mechanics has been the focus of most plant biomechanical studies, and turgor pressure was often considered as a constant and largely passive component. Nevertheless, it is increasingly accepted that turgor pressure plays a significant role in plant growth. Numerous theoretical and experimental studies suggest that turgor pressure can be both spatially inhomogeneous and actively modulated during morphogenesis. Here, we revisit the pressure-growth relationship by reviewing recent advances in investigating the interactions between cellular/tissular pressure and growth.