Coccolithophores are single-celled marine algae that produce calcified scales called coccoliths. Each scale is composed of anvil-shaped single crystals of calcite that are mechanically interlocked, constituting a remarkable example of the multi-level construction of mineralized structures. Coccolith formation starts with the nucleation of rhombohedral crystals on an organic substrate called base plate. The crystals then grow preferentially along specific directions to generate the mature structure, which is then transported to the outside of the cells. Here, we extracted forming coccoliths from Pleurochrysis carterae cells and used cryo-electron tomography to characterize, in their native, hydrated state, the three-dimensional morphology and arrangement of the crystals. Comparing the crystal morphology across three different stages of coccolith formation, we show that competition for space between adjacent crystals contributes significantly to regulation of morphology by constraining growth in certain directions. We further demonstrate that crystals within a coccolith ring develop at different rates and that each crystalline unit rests directly in contact with the base plate and overgrow the rim of the organic substrate during development.

中文翻译：

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冷冻电子层析成像技术检查了软骨菌的球形发育。

球墨石藻是单细胞海藻，会产生钙化的鳞片，称为球藻。每个刻度都由机械互锁的方解石砧状单晶组成，构成了矿化结构多级构造的显着实例。球石的形成始于菱形晶体在称为基板的有机基板上的形核。然后，晶体优先沿特定方向生长，以生成成熟的结构，然后将其运输到细胞外部。在这里，我们从白屈侧耳软骨细胞中提取了形成的球石，并使用了低温电子层析成像技术来表征其天然水合状态下的三维形态和晶体排列。比较球藻形成三个不同阶段的晶体形态，我们发现，通过限制在某些方向上的生长，相邻晶体之间的空间竞争显着促进了形态的调节。我们进一步证明，在coccolith环内的晶体以不同的速率发展，并且每个晶体单元都直接与基板接触，并在显影过程中使有机基质的边缘过度生长。