Cell Wall Mechanics Research Articles

Anisotropic Motions of Fibrils Dictated by Their Orientations in the Lamella: A Coarse-Grained Model of a Plant Cell Wall.

Plant cell walls are complex systems that exhibit the characteristics of both rigid and soft material depending on their external perturbations. The three main polymeric components in a plant primary cell wall are cellulose fibrils, hemicellulose, and pectins. These components interact in a hierarchical fashion giving rise to mesoscale structural features such as cellulose bundles, lamella stacking, and so on. Although several studies have focused on understanding these unique structural features, a clear picture linking them to cell wall mechanics is still lacking. As a first step toward this goal, a phenomenological model of plant cell wall has been developed in this work by using available experimental data to investigate the underlying connections between mesoscale structural features and the motions of fibrils during deformation. In this model cellulose fibrils exhibit motions such as angular reorientations and kinking upon forced stretching. These motions are dependent on the orientation of fibrils with respect to the stretch direction, i.e., fibrils that are at an angle to the stretch direction exhibit predominant angular reorientations, while fibrils transverse to the stretch direction undergo kinking as a result of transverse compression. Varying the chain length of pectin had negligible effects on these motions. One of the main contributions from this work is the development of a simple model that can be easily fine-tuned to test other hypotheses and extended to include additional experimental knowledge about the structural aspects of cell walls in the future.

Exocytosis and endocytosis: coordinating and fine-tuning the polar tip growth domain in pollen tubes.

Pollen tubes rapidly elongate, penetrate, and navigate through multiple female tissues to reach ovules for sperm delivery by utilizing a specialized form of polar growth known as tip growth. This process requires a battery of cellular activities differentially occurring at the apical growing region of the plasma membrane (PM), such as the differential cellular signaling involving calcium (Ca2+), phospholipids, and ROP-type Rho GTPases, fluctuation of ions and pH, exocytosis and endocytosis, and cell wall construction and remodeling. There is an emerging understanding of how at least some of these activities are coordinated and/or interconnected. The apical active ROP modulates exocytosis to the cell apex for PM and cell wall expansion differentially occurring at the tip. The differentiation of the cell wall involves at least the preferential distribution of deformable pectin polymers to the apex and non-deformable pectin polymers to the shank of pollen tubes, facilitating the apical cell expansion driven by high internal turgor pressure. Recent studies have generated inroads into how the ROP GTPase-based intracellular signaling is coordinated spatiotemporally with the external wall mechanics to maintain the tubular cell shape and how the apical cell wall mechanics are regulated to allow rapid tip growth while maintaining the cell wall integrity under the turgor pressure. Evidence suggests that exocytosis and endocytosis play crucial but distinct roles in this spatiotemporal coordination. In this review, we summarize recent advances in the regulation and coordination of the differential pectin distribution and the apical domain of active ROP by exocytosis and endocytosis in pollen tubes.

Cellular Heterogeneity in Pressure and Growth Emerges from Tissue Topology and Geometry.

Cell-to-cell heterogeneity prevails in many systems, as exemplified by cell growth, although the origin and function of such heterogeneity are often unclear. In plants, growth is physically controlled by cell wall mechanics and cell hydrostatic pressure, alias turgor pressure. Whereas cell wall heterogeneity has received extensive attention, the spatial variation of turgor pressure is often overlooked. Here, combining atomic force microscopy and a physical model of pressurized cells, we show that turgor pressure is heterogeneous in the Arabidopsis shoot apical meristem, a population of stem cells that generates all plant aerial organs. In contrast with cell wall mechanical properties that appear to vary stochastically between neighboring cells, turgor pressure anticorrelates with cell size and cell neighbor number (local topology), in agreement with the prediction by our model of tissue expansion, which couples cell wall mechanics and tissue hydraulics. Additionally, our model predicts two types of correlations between pressure and cellular growth rate, where high pressure may lead to faster- or slower-than-average growth, depending on cell wall extensibility, yield threshold, osmotic pressure, and hydraulic conductivity. The meristem exhibits one of these two regimes, depending on conditions, suggesting that, in this tissue, water conductivity may contribute to growth control. Our results unravel cell pressure as a source of patterned heterogeneity and illustrate links between local topology, cell mechanical state, and cell growth, with potential roles in tissue homeostasis.

Even Visually Intact Cell Walls in Waterlogged Archaeological Wood Are Chemically Deteriorated and Mechanically Fragile: A Case of a 170 Year-Old Shipwreck.

Structural and chemical deterioration and its impact on cell wall mechanics were investigated for visually intact cell walls (VICWs) in waterlogged archaeological wood (WAW). Cell wall mechanical properties were examined by nanoindentation without prior embedding. WAW showed more than 25% decrease of both hardness and elastic modulus. Changes of cell wall composition, cellulose crystallite structure and porosity were investigated by ATR-FTIR imaging, Raman imaging, wet chemistry, 13C-solid state NMR, pyrolysis-GC/MS, wide angle X-ray scattering, and N2 nitrogen adsorption. VICWs in WAW possessed a cleavage of carboxyl in side chains of xylan, a serious loss of polysaccharides, and a partial breakage of β-O-4 interlinks in lignin. This was accompanied by a higher amount of mesopores in cell walls. Even VICWs in WAW were severely deteriorated at the nanoscale with impact on mechanics, which has strong implications for the conservation of archaeological shipwrecks.

Genome Analysis of Lactobacillus plantarum Isolated From Some Indian Fermented Foods for Bacteriocin Production and Probiotic Marker Genes.

In this study, Lactobacillus plantarum strain DHCU70 isolated from dahi, a fermented milk product and L. plantarum strain DKP1 isolated from kinema, a fermented soybean food of India, respectively were evaluated for their bacteriocin production and probiotic properties. Both strains of L. plantarum (DHCU70 and DKP1) were found to have potent antimicrobial activity against Kocuria rhizophila ATCC 9341. Bacteriocin produced by L. plantarum strains DHCU70 and DKP1 did not exhibit inhibition of cell wall, DNA and fatty acids biosynthesis mechanisms as evaluated by whole cell reporter assays. We characterized the bacteriocin encoding genes in L. plantarum strains DHCU70 and DKP1 by whole genome sequence which consisted of a single and circular chromosome with genome size of 3.38 Mb (GC content of 44.3%) and 3.39 Mb, respectively and a GC content of 44.3%. L. plantarum DHCU70 has 3252 number of protein encoding genes comprising 89 number of RNA genes (69tRNA, 16rRNA, 4nc RNA) whereas L. plantarum DKP1 has total of 3277 number of protein encoding genes with 89 number. of RNA genes (69tRNA, 16S rRNA, 4nc RNA). Analysis revealed the presence of 20.5 kb long and 23 numbers of plantaricin encoding locus (pln locus) for production of antimicrobial compound. BAGEL analysis has shown that the pln locus of both the strains of L. plantarum showed maximum sequence similarity with plantaricin NC8 of L. plantarum NC8, originally isolated from grass silage. Annotated whole genome sequence of both strains DHCU70 and DKP1 was analyzed for the presence of probiotic marker genes. The probiotic properties of these strains of were also evaluated in vitro. Due to the presence of genes responsible for antimicrobial activity and probiotic properties, both strains of L. plantarum may be considered as a suitable probiotic candidate in food industry.

Exploring the relation between apical growth, organ formation and cell wall mechanics across land plant species

Exploring the relation between apical growth, organ formation and cell wall mechanics across land plant species

Studying cell wall mechanics using an automated confocal micro-extensometer.

Recently there has been a lot of interest in quantifying mechanical properties and responses to mechanical stress. This type of data can provide insight into how growth is regulated, the processes that enable it to occur and how stresses that build up during development feedback onto development itself. However, quantifying mechanical properties of plant cell walls is difficult as the material is heterogeneous, anisotropic and shows complex time-dependent properties as well as being subject to the complex geometries of plant tissues. It is therefore necessary to have a range of methods to enable the quantification of these properties at different resolutions and time-scales. Here we provide a guide to quantifying mechanical properties in Arabidopsis thaliana hypocotyls using a tensile testing device an automated confocal micro-extensometer (ACME). In contrast to indentation methods, tensile testing provides information on the tissue as a whole and in the plane of the sample. We also detail how to adapt the method to use it for quantifying responses to mechanical stress.

Isolation, cloning and expression analysis of cinnamyl alcohol dehydrogenase (CAD) involved in phenylpropanoid pathway of Erianthus arundinaceus, a wild relative of sugarcane.

In this study we have cloned and characterized cinnamyl alcohol dehydrogenase (CAD) involved in phenylpropanoid pathway which can be utilized for biomass modification for improved saccharification efficiency. The full length gene CAD is of 4kb containing four exons and three introns, among which the exon 1 and 2 of 88 and 116bp were conserved with sorghum and Miscanthus CADs. The coding region of CAD was identified with 1098bp open reading frame (ORF), for 365 amino acids. In the PROSITE analysis, a zinc-containing alcohol dehydrogenase signature (GHEVVGEVVEVGPEV) and an NADP-binding domain motif (GLGGLG) was identified, while the motif analysis showed unique signature sequence of "LEPYLA" at 258-264 aa which was absent in the CAD sequences of other crops. This sequence information on CAD from Erianthus a bioenergy crop might be useful for subsequent research on lignin engineering for improved biomass conversion and for unravelling the impact of lignin on cell wall mechanics.

Effects of saturated steam treatment on the cell-wall mechanics and moisture sorption properties of kenaf fibers

To improve their hygroscopicity, kenaf fibers were thermally modified by saturated steam at 180 °C for 5, 10, 20, and 40 min. The chemical structure, cellulose crystallinity, cell-wall mechanics, and moisture sorption properties of kenaf fibers were analyzed to evaluate the modification effectiveness. Mass loss and Fourier transform infrared spectroscopy spectra (FTIR) changes indicated that the lignin content and cellulose crystallinity (CrI) increased with the reduction in hemicellulose after a steam treatment, especially for a long duration. The increased CrI and relative lignin content resulted in an increased elastic modulus (Er) and hardness (H) of fiber cell walls after the steam treatment. The reduction in hydrophilic groups and increased stiffness of the cell wall after the steam treatment caused an obvious reduction in the equilibrium moisture content (EMC) at the given relative humidity (RH). It also reduced the moisture increment/decrement and sorption hysteresis during the adsorption and desorption process.

Effect of Phenol Formaldehyde Resin Penetration on the Quasi-Static and Dynamic Mechanics of Wood Cell Walls Using Nanoindentation

To evaluate the effects of phenol formaldehyde (PF) resin modification on wood cell walls, Masson pine (Pinus massoniana Lamb.) wood was impregnated with PF resin at the concentrations of 15%, 20%, 25%, and 30%, respectively. The penetration degree of PF resin into wood tracheids was quantitatively determined using confocal laser scanning microscopy (CLSM). The micromechanical properties of the control and PF-modified wood cell walls were then analyzed by the method of quasi-static nanoindentation and dynamic modulus mapping techniques. Results indicated that PF resin with low molecular weight can penetrate deeply into the wood tissues and even into the cell walls. However, the penetration degree decreased accompanying with the increase of penetration depth in wood. Both the quasi-static and dynamic mechanics of wood cell walls increased significantly after modification by the PF resin at the concentration less than 20%. The cell-wall mechanics maintained stable and even decreased as the resin concentration was increased above 20%, resulting from the increasing bulking effects such as the decreased crystallinity degree of cellulose. Furthermore, the mechanics of cell walls in the inner layer was lower than that in the outer layer of PF-modified wood.

Reactive Oxygen Species Alleviate Cell Death Induced by Thaxtomin A in Arabidopsis thaliana Cell Cultures.

Thaxtomin A (TA) is a cellulose biosynthesis inhibitor synthesized by the soil actinobacterium Streptomyces scabies, which is the main causal agent of potato common scab. TA is essential for the induction of scab lesions on potato tubers. When added to Arabidopsis thaliana cell cultures, TA induces an atypical programmed cell death (PCD). Although production of reactive oxygen species (ROS) often correlates with the induction of PCD, we observed a decrease in ROS levels following TA treatment. We show that this decrease in ROS accumulation in TA-treated cells is not due to the activation of antioxidant enzymes. Moreover, Arabidopsis cell cultures treated with hydrogen peroxide (H2O2) prior to TA treatment had significantly fewer dead cells than cultures treated with TA alone. This suggests that H2O2 induces biochemical or molecular changes in cell cultures that alleviate the activation of PCD by TA. Investigation of the cell wall mechanics using atomic force microscopy showed that H2O2 treatment can prevent the decrease in cell wall rigidity observed after TA exposure. While we cannot exclude the possibility that H2O2 may promote cell survival by altering the cellular redox environment or signaling pathways, our results suggest that H2O2 may inhibit cell death, at least partially, by reinforcing the cell wall to prevent or compensate for damages induced by TA.

Multi-Scale Evaluation of the Effect of Phenol Formaldehyde Resin Impregnation on the Dimensional Stability and Mechanical Properties of Pinus Massoniana Lamb.

The local chemistry and mechanics of the control and phenol formaldehyde (PF) resin modified wood cell walls were analyzed to illustrate the modification mechanism of wood. Masson pine (Pinus massoniana Lamb.) is most widely distributed in the subtropical regions of China. However, the dimensional instability and low strength of the wood limits its use. Thus, the wood was modified by PF resin at concentrations of 15%, 20%, 25%, and 30%, respectively. The density, surface morphology, chemical structure, cell wall mechanics, shrinking and swelling properties, and macro-mechanical properties of Masson pine wood were analyzed to evaluate the modification effectiveness. The morphology and Raman spectra changes indicated that PF resin not only filled in the cell lumens, but also penetrated into cell walls and interacted with cell wall polymers. The filling and diffusing of resin in wood resulted in improved dimensional stability, such as lower swelling and shrinking coefficients, an increase in the elastic modulus (Er) and hardness (H) of wood cell walls, the hardness of the transverse section and compressive strength of the wood. Both the dimensional stability and mechanical properties improved as the PF concentration increased to 20%; that is, a PF concentration of 20% may be preferred to modify Masson pine wood.

Modeling the nonlinear elastic behavior of plant epidermis

Cell growth and organ development in plants are often correlated with the tensile behavior of the primary cell wall. To understand the mechanical behavior of plant material, various mechanical testing techniques have been employed, such as tensile testing of excised tissue samples. The onion (Allium cepa L.) epidermis has emerged as a model system for plant tissue mechanics. In this study, we performed tensile tests on strips of adaxial onion epidermis. While the tissue appeared stiffer in the direction along the major growth axis compared with the transverse direction, the tensile strength of tissue was not significantly different between the two orientations, indicating a nontrivial link between the cell wall and tissue mechanical anisotropy. Importantly, we observed the stress–strain behavior of the onion epidermis under tension to be highly nonlinear. Several hyperelastic models were fitted to the test data to evaluate their capacity to describe the nonlinear deformation of onion epidermis. The Yeoh hyperelastic model could successfully simulate the uniaxial tensile test data. This study suggests that accounting for nonlinearity in the deformation of the primary tissue may be essential for the accurate interpretation of mechanical test data, and a better understanding of the mechanics of the primary plant cell wall.

A promising technology based on photoelectrocatalysis against Mycobacterium tuberculosis in water disinfection

ABSTRACT Mycobacterium tuberculosis is highly infectious, persistent and has been detected in more than one quarter of the world’s population. It is notoriously resistant to sterilization and disinfection procedures, largely due to an unusual hydrophobic cell wall and effective defense mechanisms against oxidative stress. This work shows an effective method to reduce M. tuberculosis quantity in water by using Ti/TiO2 nanotubes electrodes bare and coated with Ag nanoparticles by using photoelectrocatalytic oxidation process. The results have indicated 99.999% of inactivation of a solution spiked with standard and resistant strains of 1×104 CFU mL−1 M. tuberculosis after 5 min of treatment at Ti/TiO2 photoanode in 0.05 mol L−1 Na2SO4 (pH 6) under applied potential of + 1.5 V versus Ag/AgCl and UV irradiation. The mycobacteria degradation was monitored by dissolved total organic carbon (TOC) removal, carbohydrate release, chromatography coupled to mass spectroscopy measurements and it is slightly superior to photocatalysis and photolysis processes. All the results corroborated with the complete inactivation and degradation of the byproducts generated during cell lysis.

Methods to quantify primary plant cell wall mechanics.

The primary plant cell wall is a dynamically regulated composite material of multiple biopolymers that forms a scaffold enclosing the plant cells. The mechanochemical make-up of this polymer network regulates growth, morphogenesis, and stability at the cell and tissue scales. To understand the dynamics of cell wall mechanics, and how it correlates with cellular activities, several experimental frameworks have been deployed in recent years to quantify the mechanical properties of plant cells and tissues. Here we critically review the application of biomechanical tool sets pertinent to plant cell mechanics and outline some of their findings, relevance, and limitations. We also discuss methods that are less explored but hold great potential for the field, including multiscale in silico mechanical modeling that will enable a unified understanding of the mechanical behavior across the scales. Our overview reveals significant differences between the results of different mechanical testing techniques on plant material. Specifically, indentation techniques seem to consistently report lower values compared with tensile tests. Such differences may in part be due to inherent differences among the technical approaches and consequently the wall properties that they measure, and partly due to differences between experimental conditions.

Systematic mapping of cell wall mechanics in the regulation of cell morphogenesis

Walled cells of plants, fungi, and bacteria come with a large range of shapes and sizes, which are ultimately dictated by the mechanics of their cell wall. This stiff and thin polymeric layer encases the plasma membrane and protects the cells mechanically by opposing large turgor pressure derived mechanical stresses. To date, however, we still lack a quantitative understanding for how local and/or global mechanical properties of the wall support cell morphogenesis. Here, we combine subresolution imaging and laser-mediated wall relaxation to quantitate subcellular values of wall thickness (h) and bulk elastic moduli (Y) in large populations of live mutant cells and in conditions affecting cell diameter in the rod-shaped model fission yeast. We find that lateral wall stiffness, defined by the surface modulus, σ = hY, robustly scales with cell diameter. This scaling is valid across tens of mutants spanning various functions-within the population of individual isogenic strains, along single misshaped cells, and even across the fission yeasts clade. Dynamic modulations of cell diameter by chemical and/or mechanical means suggest that the cell wall can rapidly adapt its surface mechanics, rendering stretched wall portions stiffer than unstretched ones. Size-dependent wall stiffening constrains diameter definition and limits size variations; it may also provide an efficient means to keep elastic strains in the wall below failure strains, potentially promoting cell survival. This quantitative set of data impacts our current understanding of the mechanics of cell walls and its contribution to morphogenesis.

Coupling water fluxes with cell wall mechanics in a multicellular model of plant development.

The growth of plant organs is a complex process powered by osmosis that attracts water inside the cells; this influx induces simultaneously an elastic extension of the walls and pressure in the cells, called turgor pressure; above a threshold, the walls yield and the cells grow. Based on Lockhart’s seminal work, various models of plant morphogenesis have been proposed, either for single cells, or focusing on the wall mechanical properties. However, the synergistic coupling of fluxes and wall mechanics has not yet been fully addressed in a multicellular model. This work lays the foundations of such a model, by simplifying as much as possible each process and putting emphasis on the coupling itself. Its emergent properties are rich and can help to understand plant morphogenesis. In particular, we show that the model can display a new type of lateral inhibitory mechanism that amplifies growth heterogeneities due e.g to cell wall loosening.

Dynamics of intracellular mannan and cell wall folding in the drought responses of succulent Aloe species.

Plants have evolved a multitude of adaptations to survive extreme conditions. Succulent plants have the capacity to tolerate periodically dry environments, due to their ability to retain water in a specialized tissue, termed hydrenchyma. Cell wall polysaccharides are important components of water storage in hydrenchyma cells. However, the role of the cell wall and its polysaccharide composition in relation to drought resistance of succulent plants are unknown. We investigate the drought response of leaf‐succulent Aloe (Asphodelaceae) species using a combination of histological microscopy, quantification of water content, and comprehensive microarray polymer profiling. We observed a previously unreported mode of polysaccharide and cell wall structural dynamics triggered by water shortage. Microscopical analysis of the hydrenchyma cell walls revealed highly regular folding patterns indicative of predetermined cell wall mechanics in the remobilization of stored water and the possible role of homogalacturonan in this process. The in situ distribution of mannans in distinct intracellular compartments during drought, for storage, and apparent upregulation of pectins, imparting flexibility to the cell wall, facilitate elaborate cell wall folding during drought stress. We conclude that cell wall polysaccharide composition plays an important role in water storage and drought response in Aloe.

Mathematical principles and models of plant growth mechanics: from cell wall dynamics to tissue morphogenesis.

Plant growth research produces a catalogue of complex open questions. We argue that plant growth is a highly mechanical process, and that mathematics gives an underlying framework with which to probe its fundamental unrevealed mechanisms. This review serves to illustrate the biological insights afforded by mathematical modelling and demonstrate the breadth of mathematically rich problems available within plant sciences, thereby promoting a mutual appreciation across the disciplines. On the one hand, we explain the general mathematical principles behind mechanical growth models; on the other, we describe how modelling addresses specific problems in microscale cell wall mechanics, tip growth, morphogenesis, and stress feedback. We conclude by identifying possible future directions for both biologists and mathematicians, including as yet unanswered questions within various topics, stressing that interdisciplinary collaboration is vital for tackling the challenge of understanding plant growth mechanics.

THE ROLE OF POTASSIUM AND CALSIUM IN IMPROVING THE QUALITY AND SHELF LIFE OF TOMATO (Lycopersicum esculentum var. servo)

Tomato has the characteristics natural to damage. Damage fruits are caused by destitute of fruit quality and sensory attributes. The loss of tomato production on harvest in developing countries reached 50% due to the long duration of tomato distribution. Servo varieties of tomatoes are in demand by farmers because of their genetic advantages, high productivity, and abundant fruit weights. The shortage of servo varieties of tomatoes is the short shelf life of fruit, which is seven days after harvest. Short shelf life is influenced by fruit thickness and fruit hardness. In improving the quality and shelf life of tomatoes, potassium (K) nutrition plays a role in photosynthetic translocation, strengthens the cell wall, and involved in the lignification process of sclerenchyma tissue. Tomatoes, as climacteric fruits have a high respiration rate influenced by ethylene. Ethylene production can be inhibited by calcium chloride (CaCl2) application by strengthening the cell wall mechanism, cross-link with pectin, and increase the cell wall regeneration can change the texture of the fruit become harder, and it reduces sensitivity to physiological damage. Based on the treatment of this research, the quality and shelf life of servo varieties of tomato is increased.