Nanoprobe crystallographic orientation studies of isolated shield elements of the coccolithophore species Emiliania huxleyi
Nanoprobe crystallographic orientation studies of isolated shield elements of the coccolithophore species Emiliania huxleyi
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DOI：
10.1127/0935-1221/2014/0026-2365
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发表时间：
2014-08-01
影响因子：
2.1
通讯作者：
Schmahl, Wolfgang W.
中科院分区：
文献类型：
--
作者：
Hoffmann, Ramona;Wochnik, Angela S.;Schmahl, Wolfgang W.
球石藻类产生由亚微米级方解石晶体组成的结构精细的骨骼。为了了解方解石在纳米尺度球球中的结晶和组装，用透射电子显微镜成像、选区电子衍射和纳米探针电子衍射研究了结构单元的晶体取向和交错。利用聚焦离子束切割法对球石生物体物种埃米利亚纳的球石进行切片，以获得适当取向的靶制备样品。我们能够检测和分析V单元，它被R单元过度生长。对于V形单元，[001]方向点垂直于球石平面，而[110]轴与球石环相切。R单位c轴平行，b轴垂直球石平面，从而证实了基于扫描电子显微镜和光学显微镜的R-和V-模型。此外，我们还证明了单个节段的单个R单位的远端和近端屏蔽元件彼此倾斜了4度+/-1度。这种取向的改变是获得球石的扁平圆顶特征所必需的，这是形成球球所必需的。远端和近端屏蔽元件之间的取向变化是连续的。
Coccolithophore algae produce elaborately structured skeletons composed of sub-micrometer-scale calcite crystals. In order to understand calcite crystallization and assembly in a coccosphere with nanoscale resolution, the crystal orientation and interdigitation of the structural units were investigated by transmission electron microscopy imaging, selected-area and nano-probe electron diffraction. Focused ion beam sectioning of coccoliths of the coccolithophore species Emiliania huxleyi is used to obtain target-prepared specimens in suitable orientation. We were able to detect and analyze the V-unit, which is overgrown by the R-unit. For the V-unit the [001] direction points perpendicular to the coccolith plane while the [110] axis is tangential to the coccolith ring. The R-unit c-axis is parallel and the b-axis is perpendicular to the coccolith plane, thus confirming the R- and V-model which was based on scanning electron microscopy and optical microscopy. Furthermore we show that the distal- and the proximal shield element of an individual R-unit of a single segment are tilted by 4 degrees +/- 1 degrees with respect to each other. This orientation change is required to obtain the flat domed character of the coccoliths, which is necessary to form the coccosphere. The orientation change between the distal- and the proximal shield element appears continuous.