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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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Frequency distribution of Young's moduli (E) for stained and unstained structural components.Data were grouped into 3 ‘stiffness’ categories. Number of samples in each category: 0.3<E<0.99 MPa n = 20; 1<E<2.99 MPa n = 32; E>3 MPa n = 37.
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pone-0109089-g004: Frequency distribution of Young's moduli (E) for stained and unstained structural components.Data were grouped into 3 ‘stiffness’ categories. Number of samples in each category: 0.3<E<0.99 MPa n = 20; 1<E<2.99 MPa n = 32; E>3 MPa n = 37.

Mentions: Measurements were conducted on short chains of L. undulatum (2–6 cells per chain). Overall, local elasticity, parameterized as Young's modulus (E), was highly variable, spanning a wide range from 0.25 to 9 MPa (n = 85 locations; 35 cells from 14 chains were analyzed in total). Within a single chain, local stiffness varied by a factor of 3–6. When grouped according to location (girdle at the cell center, valve mantle, valve edge and marginal ridge) there was no significant difference in mean Young's modulus between locations, but variability within each region was high (Figure 3). However, when the elasticity of stained vs. unstained regions was compared, patterns began to emerge. Young's modulus values from all sampling locations were grouped into 3 ‘stiffness’ categories: E≤1 MPa (‘soft’), 1.1<E≤3 MPa (‘intermediate’) and 3<E≤9 MPa (‘stiff’). Within the ‘soft’ group, 80% of the samples were associated with stained regions while the ‘stiff’ group primarily comprised samples from unstained regions (78%, Figure 4). Overall, Young's modulus of stained regions was significantly lower than that of unstained regions (Kruskal Wallis P<0.01, ANOVA P<0.01). For cells that divided during the period of incubation, newly formed thecae and marginal ridges were significantly ‘softer’ than their counterparts inherited from the parent cell (Kruskal Wallis P = 0.03; ANOVA P = 0.02). Values from the latter were not significantly different from values obtained from cells that did not divide (Kruskal Wallis/ANOVA P = 0.25).


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)

Frequency distribution of Young's moduli (E) for stained and unstained structural components.Data were grouped into 3 ‘stiffness’ categories. Number of samples in each category: 0.3<E<0.99 MPa n = 20; 1<E<2.99 MPa n = 32; E>3 MPa n = 37.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0109089-g004: Frequency distribution of Young's moduli (E) for stained and unstained structural components.Data were grouped into 3 ‘stiffness’ categories. Number of samples in each category: 0.3<E<0.99 MPa n = 20; 1<E<2.99 MPa n = 32; E>3 MPa n = 37.
Mentions: Measurements were conducted on short chains of L. undulatum (2–6 cells per chain). Overall, local elasticity, parameterized as Young's modulus (E), was highly variable, spanning a wide range from 0.25 to 9 MPa (n = 85 locations; 35 cells from 14 chains were analyzed in total). Within a single chain, local stiffness varied by a factor of 3–6. When grouped according to location (girdle at the cell center, valve mantle, valve edge and marginal ridge) there was no significant difference in mean Young's modulus between locations, but variability within each region was high (Figure 3). However, when the elasticity of stained vs. unstained regions was compared, patterns began to emerge. Young's modulus values from all sampling locations were grouped into 3 ‘stiffness’ categories: E≤1 MPa (‘soft’), 1.1<E≤3 MPa (‘intermediate’) and 3<E≤9 MPa (‘stiff’). Within the ‘soft’ group, 80% of the samples were associated with stained regions while the ‘stiff’ group primarily comprised samples from unstained regions (78%, Figure 4). Overall, Young's modulus of stained regions was significantly lower than that of unstained regions (Kruskal Wallis P<0.01, ANOVA P<0.01). For cells that divided during the period of incubation, newly formed thecae and marginal ridges were significantly ‘softer’ than their counterparts inherited from the parent cell (Kruskal Wallis P = 0.03; ANOVA P = 0.02). Values from the latter were not significantly different from values obtained from cells that did not divide (Kruskal Wallis/ANOVA P = 0.25).

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