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Judging diatoms by their cover: variability in local elasticity of Lithodesmium undulatum undergoing cell division.

Karp-Boss L, Gueta R, Rousso I - PLoS ONE (2014)

Bottom Line: Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells.This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle.Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle.

View Article: PubMed Central - PubMed

Affiliation: School of Marine Sciences, University of Maine, Orono, Maine, United States of America.

ABSTRACT
Unique features of diatoms are their intricate cell covers (frustules) made out of hydrated, amorphous silica. The frustule defines and maintains cell shape and protects cells against grazers and pathogens, yet it must allow for cell expansion during growth and division. Other siliceous structures have also evolved in some chain-forming species as means for holding neighboring cells together. Characterization and quantification of mechanical properties of these structures are crucial for the understanding of the relationship between form and function in diatoms, but thus far only a handful of studies have addressed this issue. We conducted micro-indentation experiments, using atomic force microscopy (AFM), to examine local variations in elastic (Young's) moduli of cells and linking structures in the marine, chain-forming diatom Lithodesmium undulatum. Using a fluorescent tracer that is incorporated into new cell wall components we tested the hypothesis that new siliceous structures differ in elastic modulus from their older counterparts. Results show that the local elastic modulus is a highly dynamic property. Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells. This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle. Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle.

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Related in: MedlinePlus

Measuring the stiffness of the cell using indentation type experiments.Averaged force distance curves for deflection of the cantilever (reference on a glass slide; red curve) and for a cell (black curve) measured in the marginal ridge (A) and valve (B) regions. To set the tip-sample contact point (Z0) to a distance of zero, the curves were shifted along the Z-axis. Approximately 100 consecutive curves were acquired for each experiment. The indentation depth is defined as the difference between the Z position of the cell and cantilever deflection at a given loading force. The Young's modulus of the sample was determined by fitting the data with the Hertz model (see Methods).
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pone-0109089-g002: Measuring the stiffness of the cell using indentation type experiments.Averaged force distance curves for deflection of the cantilever (reference on a glass slide; red curve) and for a cell (black curve) measured in the marginal ridge (A) and valve (B) regions. To set the tip-sample contact point (Z0) to a distance of zero, the curves were shifted along the Z-axis. Approximately 100 consecutive curves were acquired for each experiment. The indentation depth is defined as the difference between the Z position of the cell and cantilever deflection at a given loading force. The Young's modulus of the sample was determined by fitting the data with the Hertz model (see Methods).

Mentions: Prior to analysis, each set of successive curves was carefully reviewed and examined for shifts in behavior that might indicate potential damage to the sampled area in the course of the measurement. Sets for which shifts in the shape of the curve were detected and/or the spread between curves was large were discarded from the analysis. Only the approaching part of the force-distance curves was used for analysis. Each curve from a set of successive force-distance curves was shifted to set the deflection in the non-contact mode to zero. Averaged force-distance curves were then converted from deflection units (V) to loading forces (N) by multiplying by the deflection sensitivity (in nm/V, derived from a force-distance curve performed on glass) and the spring constant of the cantilever (N/m). Example of force-distance curves from valve and marginal ridge regions are presented in Figure 2. Young's moduli (elastic moduli, E) were estimated by fitting a modified Hertz model, for a spherical probe [27], to the averaged force-distance curves, using a custom MATLAB code. Samples that did not show good fit to the model were discarded because their E could not be estimated. E values for the different structural features, as well as stained and non-stained regions were grouped. Statistical differences between means and medians, respectively, were tested using parametric (ANOVA) and nonparametric (Kruskal-Wallis) statistics at a level of ≤0.05.


Judging diatoms by their cover: variability in local elasticity of Lithodesmium undulatum undergoing cell division.

Karp-Boss L, Gueta R, Rousso I - PLoS ONE (2014)

Measuring the stiffness of the cell using indentation type experiments.Averaged force distance curves for deflection of the cantilever (reference on a glass slide; red curve) and for a cell (black curve) measured in the marginal ridge (A) and valve (B) regions. To set the tip-sample contact point (Z0) to a distance of zero, the curves were shifted along the Z-axis. Approximately 100 consecutive curves were acquired for each experiment. The indentation depth is defined as the difference between the Z position of the cell and cantilever deflection at a given loading force. The Young's modulus of the sample was determined by fitting the data with the Hertz model (see Methods).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4206279&req=5

pone-0109089-g002: Measuring the stiffness of the cell using indentation type experiments.Averaged force distance curves for deflection of the cantilever (reference on a glass slide; red curve) and for a cell (black curve) measured in the marginal ridge (A) and valve (B) regions. To set the tip-sample contact point (Z0) to a distance of zero, the curves were shifted along the Z-axis. Approximately 100 consecutive curves were acquired for each experiment. The indentation depth is defined as the difference between the Z position of the cell and cantilever deflection at a given loading force. The Young's modulus of the sample was determined by fitting the data with the Hertz model (see Methods).
Mentions: Prior to analysis, each set of successive curves was carefully reviewed and examined for shifts in behavior that might indicate potential damage to the sampled area in the course of the measurement. Sets for which shifts in the shape of the curve were detected and/or the spread between curves was large were discarded from the analysis. Only the approaching part of the force-distance curves was used for analysis. Each curve from a set of successive force-distance curves was shifted to set the deflection in the non-contact mode to zero. Averaged force-distance curves were then converted from deflection units (V) to loading forces (N) by multiplying by the deflection sensitivity (in nm/V, derived from a force-distance curve performed on glass) and the spring constant of the cantilever (N/m). Example of force-distance curves from valve and marginal ridge regions are presented in Figure 2. Young's moduli (elastic moduli, E) were estimated by fitting a modified Hertz model, for a spherical probe [27], to the averaged force-distance curves, using a custom MATLAB code. Samples that did not show good fit to the model were discarded because their E could not be estimated. E values for the different structural features, as well as stained and non-stained regions were grouped. Statistical differences between means and medians, respectively, were tested using parametric (ANOVA) and nonparametric (Kruskal-Wallis) statistics at a level of ≤0.05.

Bottom Line: Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells.This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle.Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle.

View Article: PubMed Central - PubMed

Affiliation: School of Marine Sciences, University of Maine, Orono, Maine, United States of America.

ABSTRACT
Unique features of diatoms are their intricate cell covers (frustules) made out of hydrated, amorphous silica. The frustule defines and maintains cell shape and protects cells against grazers and pathogens, yet it must allow for cell expansion during growth and division. Other siliceous structures have also evolved in some chain-forming species as means for holding neighboring cells together. Characterization and quantification of mechanical properties of these structures are crucial for the understanding of the relationship between form and function in diatoms, but thus far only a handful of studies have addressed this issue. We conducted micro-indentation experiments, using atomic force microscopy (AFM), to examine local variations in elastic (Young's) moduli of cells and linking structures in the marine, chain-forming diatom Lithodesmium undulatum. Using a fluorescent tracer that is incorporated into new cell wall components we tested the hypothesis that new siliceous structures differ in elastic modulus from their older counterparts. Results show that the local elastic modulus is a highly dynamic property. Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells. This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle. Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle.

Show MeSH
Related in: MedlinePlus