An official website of the United States government
Abstract Mechanical properties, size and geometry of cells, and internal turgor pressure greatly influence cell morphogenesis. Computational models of cell growth require values for wall elastic modulus and turgor pressure, but very few experiments have been designed to validate the results using measurements that deform the entire thickness of the cell wall. New wall material is synthesized at the inner surface of the cell such that full-thickness deformations are needed to quantify relevant changes associated with cell development. Here, we present an integrated, experimental–computational approach to analyze quantitatively the variation of elastic bending behavior in the primary cell wall of living Arabidopsis (Arabidopsis thaliana) pavement cells and to measure turgor pressure within cells under different osmotic conditions. This approach used laser scanning confocal microscopy to measure the 3D geometry of single pavement cells and indentation experiments to probe the local mechanical responses across the periclinal wall. The experimental results were matched iteratively using a finite element model of the experiment to determine the local mechanical properties and turgor pressure. The resulting modulus distribution along the periclinal wall was nonuniform across the leaf cells studied. These results were consistent with the characteristics of plant cell walls which have a heterogeneous organization. The results and model allowed the magnitude and orientation of cell wall stress to be predicted quantitatively. The methods also serve as a reference for future work to analyze the morphogenetic behaviors of plant cells in terms of the heterogeneity and anisotropy of cell walls.
more »
« less
The semi-automated development of plant cell wall finite element models
Abstract This study presents a methodology for a high-throughput digitization and quantification process of plant cell walls characterization, including the automated development of two-dimensional finite element models. Custom algorithms based on machine learning can also analyze the cellular microstructure for phenotypes such as cell size, cell wall curvature, and cell wall orientation. To demonstrate the utility of these models, a series of compound microscope images of both herbaceous and woody representatives were observed and processed. In addition, parametric analyses were performed on the resulting finite element models. Sensitivity analyses of the structural stiffness of the resulting tissue based on the cell wall elastic modulus and the cell wall thickness; demonstrated that the cell wall thickness has a three-fold larger impact of tissue stiffness than cell wall elastic modulus.
more »
« less
- Award ID(s):
- 1826715
- PAR ID:
- 10390312
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Plant Methods
- Volume:
- 19
- Issue:
- 1
- ISSN:
- 1746-4811
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Stalk lodging in the monocot Zea mays is an important agricultural issue that requires the development of a genome-to-phenome framework, mechanistically linking intermediate and high-level phenotypes. As part of that effort, tools are needed to enable better mechanistic understanding of the microstructure in herbaceous plants. A method was therefore developed to create finite element models using CT scan data for Zea mays. This method represents a pipeline for processing the image stacks and developing the finite element models. 2-dimensional finite element models, 3-dimensional watertight models, and 3-dimensional voxel-based finite element models were developed. The finite element models contain both the cell and cell wall structures that can be tested in silico for phenotypes such as structural stiffness and predicted tissue strength. This approach was shown to be successful, and a number of example analyses were presented to demonstrate its usefulness and versatility. This pipeline is important for two reasons: (1) it helps inform which microstructure phenotypes should be investigated to breed for more lodging-resistant stalks, and (2) represents an essential step in the development of a mechanistic hierarchical framework for the genome-to-phenome modeling of herbaceous plant stalk lodging.more » « less
-
Increasing antibiotic resistance in bacteria is a critical issue that often leads to infections or other morbidities. Mechanical properties of the bacterial cell wall, such as thickness or elastic modulus, may contribute to the ability of a bacterial cell to resist antibiotics. Techniques like atomic force microscopy (AFM) are used to quantify bacterial cell mechanical properties and image cell structures at nanoscale resolutions. An additional benefit of AFM is the ability to probe samples submerged in liquids, meaning that live bacteria can be imaged or evaluated in environments that more accurately simulate in vivo conditions as compared to other methods like electron microscopy. However, because AFM measurements are highly sensitive to small perturbations in the deflection of the tip of a sensor probe brought into contact with the specimen, immobilization of bacteria prior to measurement is essential for accurate measurements. Traditional chemical fixatives crosslink the molecules within the bacterial cell wall, which prevent the bacteria from locomotion. While effective for imaging, chemical crosslinkers are known to affect the measured stiffness of eukaryotic cells and also may affect the measured stiffness of the bacterial cell wall. Alternative immobilization methods include Cell-Tak™, an adhesive derived from marine mussels that does not interact with the bacterial wall and filters with known pore sizes which entrap bacteria. Previous studies have examined the effect of these immobilization methods on successful imaging of bacteria but have not addressed differences in measured modulus. This study compares the effects of immobilization methods including chemical fixatives, mechanical entrapment in filters, and Cell-Tak™ on the stiffness of the bacterial cell wall as measured by force spectroscopy.more » « less
-
null (Ed.)Abstract Plant cell deformations are driven by cell pressurization and mechanical constraints imposed by the nanoscale architecture of the cell wall, but how these factors are controlled at the genetic and molecular levels to achieve different types of cell deformation is unclear. Here, we used stomatal guard cells to investigate the influences of wall mechanics and turgor pressure on cell deformation and demonstrate that the expression of the pectin-modifying gene PECTATE LYASE LIKE12 (PLL12) is required for normal stomatal dynamics in Arabidopsis thaliana. Using nanoindentation and finite element modeling to simultaneously measure wall modulus and turgor pressure, we found that both values undergo dynamic changes during induced stomatal opening and closure. PLL12 is required for guard cells to maintain normal wall modulus and turgor pressure during stomatal responses to light and to tune the levels of calcium cross-linked pectin in guard cell walls. Guard cell-specific knockdown of PLL12 caused defects in stomatal responses and reduced leaf growth, which were associated with lower cell proliferation but normal cell expansion. Together, these results force us to revise our view of how wall-modifying genes modulate wall mechanics and cell pressurization to accomplish the dynamic cellular deformations that underlie stomatal function and tissue growth in plants.more » « less
-
Pulmonary arterial hypertension (PAH) presents a significant challenge to right ventricular (RV) function due to progressive pressure overload, necessitating adaptive remodeling in the form of increased wall thickness, enhanced myocardial contractility and stiffness to maintain cardiac performance. However, the impact of these remodeling mechanisms on RV mechanics in not clearly understood. In addition, there is a lack of quantitative understanding of how each mechanism individually influences RV mechanics. Utilizing experimental data from a rat model of PAH at three distinct time points, we developed biventricular finite element models to investigate how RV stress and strain evolved with PAH progression. The finite element models were fitted to hemodynamic and morphological data to represent different disease stages and used to analyze the impact of RV remodeling as well as the altered RV pressure. Furthermore, we performed a number of theoretical simulation studies with different combinations of morphological and physiological remodeling, to assess and quantify their individual impact on overall RV load and function. Our findings revealed a substantial 4-fold increase in RV stiffness and a transient 2-fold rise in contractility, which returned to baseline by week 12. These changes in RV material properties in addition to the 2-fold increase in wall thickness significantly mitigated the increase in wall stress and strain caused by the progressive increase in RV afterload. Despite the PAH-induced cases showing increased wall stress and strain at end-diastole and end-systole compared to the control, our simulations suggest that without the observed remodeling mechanisms, the increase in stress and strain would have been much more pronounced. Our model analysis also indicated that while changes in the RV’s material properties–particularly increased RV stiffness - have a notable effect on its mechanics, the primary compensatory factor limiting the stress and strain increase in the early stages of PAH was the significant increase in wall thickness. These findings underscore the importance of RV remodeling in managing the mechanical burden on the right ventricle due to pressure overload.more » « less
