Dynamics of silica cell wall morphogenesis in the diatom Cyclotella cryptica: Substructure formation and the role of microfilaments

Compartmental Analysis Suggests Macropinocytosis at the Onset of Diatom Valve Formation

“…It remains to be shown whether or not this process takes place by: 1) 'classical' pinocytosis in which multiple smaller vesicles are involved, or 2) macropinocytosis in which one larger vesicle is formed which transforms to become the initial SDV. The macropinocytosis hypothesis is supported by recent 3-D ultrastructural studies on SDV transformations [16] in which actin filaments are specifically involved in molding and/or compressing the SDV at the cleavage furrow [17]; SDV transformation agrees well with an earlier observed high membrane activity in dividing diatom cells [22,23]. Furthermore, in plants a similar uptake mechanism for silicon has been observed [24].…”

“…The results prompted us to further focus on macropinocytosis-mediated Si uptake ( If this mechanism is applicable, the larger vesicle formed intracellularly subsequently may be compressed towards the cleavage furrow by cellular and membrane activity [16,17,22,23]; especially when simultaneously water is expelled [20,35] the concentration of silicic acid to the threshold for autopolymerization would be achieved [14,15]. For T. pseudonana it is demonstrated that silica is formed in the most compressed region of the SDV [16].…”

“…Ionic strength determines the degree of condensation of the silica and affects the nanostructure of the solid silica formed in diatoms [7]. Noteworthy is that in diatoms early valve formation coincides with nanostructuring of the primer two-dimensional silica base [16,17]. The impact of reaction conditions on silica polymerization in diatom frustule formation suggests that cellular transport routes during which polymerization of accumulated silicon species could occur are not likely to be involved in valve formation [4,7].…”

“…Silicon in diatom cells (excluding the silica of the frustule) has been proposed to be present in a precondensed silica sol-like form [18], while during valve formation organo-silicon interactions occur [19]. The exact localization of these silicon species and their accumulation outside the SDV is under debate; distinct intracellularly confined silicon pools have never been detected [17,20,21], except the one in the SDV and the random distribution of very low silicon levels inside various cellular compartments [4,5,20,21]. Thus, the absence of distinctive larger intracellular silicon pools is certainly not in line with an expected high uptake and intracellular transport of silicon required for valve formation.…”

Developmental plasticity and genotype–environment interactions influence valve morphology in theCyclotella meneghinianaspecies complex (Bacillariophyceae)

“…striae, fultoportulae) are not yet completely understood, microtubules and microfilamentous actin are known to play significant roles in the positioning of pattern elements of the valve. Tesson & Hildebrand (2010) revealed that valve formation proceeds with actin and the silica deposition vesicle interdigitated. They also revealed that misalignment of ribs and mispositioning of portulae occurs under the influence of microtubule inhibitors in C. cryptica.…”