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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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Frustule and chain morphology.(A) A schematic structure of the frustule (modified after [1]). The frustule consists of two overlapping elements, or thecae, that fit together like the two halves of a Petri dish. Each theca is capped with a distinctive structure called a valve. A series of thin, overlapping bands of silica, termed girdle elements (or girdle bands), extends from the rim of the valve forming the sidewall of the theca. The two thecae are identically shaped but differ slightly in diameter; one fits within the other, with their girdle elements partially overlapping, to form an enclosed structure around the cell's protoplasm. The frustule is perforated with nanometer-scale pores arranged in species-specific, ornate patterns that allow the exchange of solutes between the cell and the environment. (B) A light-microscope image of L. undulatum. (C) SEM image of L. undulatum. (D) Epifluorescence image of L. undulatum after staining with PDMPO. The green region indicates a valve and marginal ridges that were formed during the incubation time with PDMPO.
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pone-0109089-g001: Frustule and chain morphology.(A) A schematic structure of the frustule (modified after [1]). The frustule consists of two overlapping elements, or thecae, that fit together like the two halves of a Petri dish. Each theca is capped with a distinctive structure called a valve. A series of thin, overlapping bands of silica, termed girdle elements (or girdle bands), extends from the rim of the valve forming the sidewall of the theca. The two thecae are identically shaped but differ slightly in diameter; one fits within the other, with their girdle elements partially overlapping, to form an enclosed structure around the cell's protoplasm. The frustule is perforated with nanometer-scale pores arranged in species-specific, ornate patterns that allow the exchange of solutes between the cell and the environment. (B) A light-microscope image of L. undulatum. (C) SEM image of L. undulatum. (D) Epifluorescence image of L. undulatum after staining with PDMPO. The green region indicates a valve and marginal ridges that were formed during the incubation time with PDMPO.

Mentions: Diatoms have long been recognized as one of the most important groups of photosynthetic organisms in aquatic environments. They contribute significantly to primary production in oceans and lakes and consequently play significant roles in food-web dynamics and biogeochemical cycling. Diatoms' hallmarks are the intricate, silicified cell walls, or frustules, that they form (Figure 1). The frustule is a composite material, made primarily of amorphous, hydrated silica and organic compounds that are tightly associated with the silica [1]. The structure and biochemical composition of the organic matrix has not been fully characterized, but several organic compounds have been identified. These include highly modified peptides (silafins), long-chain polyamines and acidic polypeptides [1], [2], polysaccharides [3], [4], [5] and chitin [6].


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)

Frustule and chain morphology.(A) A schematic structure of the frustule (modified after [1]). The frustule consists of two overlapping elements, or thecae, that fit together like the two halves of a Petri dish. Each theca is capped with a distinctive structure called a valve. A series of thin, overlapping bands of silica, termed girdle elements (or girdle bands), extends from the rim of the valve forming the sidewall of the theca. The two thecae are identically shaped but differ slightly in diameter; one fits within the other, with their girdle elements partially overlapping, to form an enclosed structure around the cell's protoplasm. The frustule is perforated with nanometer-scale pores arranged in species-specific, ornate patterns that allow the exchange of solutes between the cell and the environment. (B) A light-microscope image of L. undulatum. (C) SEM image of L. undulatum. (D) Epifluorescence image of L. undulatum after staining with PDMPO. The green region indicates a valve and marginal ridges that were formed during the incubation time with PDMPO.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0109089-g001: Frustule and chain morphology.(A) A schematic structure of the frustule (modified after [1]). The frustule consists of two overlapping elements, or thecae, that fit together like the two halves of a Petri dish. Each theca is capped with a distinctive structure called a valve. A series of thin, overlapping bands of silica, termed girdle elements (or girdle bands), extends from the rim of the valve forming the sidewall of the theca. The two thecae are identically shaped but differ slightly in diameter; one fits within the other, with their girdle elements partially overlapping, to form an enclosed structure around the cell's protoplasm. The frustule is perforated with nanometer-scale pores arranged in species-specific, ornate patterns that allow the exchange of solutes between the cell and the environment. (B) A light-microscope image of L. undulatum. (C) SEM image of L. undulatum. (D) Epifluorescence image of L. undulatum after staining with PDMPO. The green region indicates a valve and marginal ridges that were formed during the incubation time with PDMPO.
Mentions: Diatoms have long been recognized as one of the most important groups of photosynthetic organisms in aquatic environments. They contribute significantly to primary production in oceans and lakes and consequently play significant roles in food-web dynamics and biogeochemical cycling. Diatoms' hallmarks are the intricate, silicified cell walls, or frustules, that they form (Figure 1). The frustule is a composite material, made primarily of amorphous, hydrated silica and organic compounds that are tightly associated with the silica [1]. The structure and biochemical composition of the organic matrix has not been fully characterized, but several organic compounds have been identified. These include highly modified peptides (silafins), long-chain polyamines and acidic polypeptides [1], [2], polysaccharides [3], [4], [5] and chitin [6].

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