SINGLE CRYSTALLINE NATURE OF COCCOLITH ELEMENTS OF THE MARINE ALGA EMILIANIA-HUXLEYI AS DETERMINED BY ELECTRON-DIFFRACTION AND HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY
SINGLE CRYSTALLINE NATURE OF COCCOLITH ELEMENTS OF THE MARINE ALGA EMILIANIA-HUXLEYI AS DETERMINED BY ELECTRON-DIFFRACTION AND HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY
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DOI：
10.1098/rspb.1988.0057
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发表时间：
1988-09-22
期刊：
影响因子：
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通讯作者：
SPARKS, NHC
中科院分区：
文献类型：
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作者：
MANN, S;SPARKS, NHC
电子衍射仪和高分辨电子显微镜表明，构成海藻球石的放射状节段是方解石的单个单晶单位。板状下元件的顶面和底面对应于(1210)和(1210)面，并且[0001]方向(c轴)平行于这些面并且沿着下元件和上元件的伸长方向定向。[1010]方向垂直于伸长方向，并对应于锤头延伸部在上部元件中生长的持续时间。从上方观察时，每个放射状部分都显示出惯用手。下部元件的外周边缘被(1014)和(1018)三方面截断，其中(1018)面更广泛地展开，并且当从上方观察时总是位于左侧，表明(1210)面在下层基板表面上的特定生长。能量色散X射线分析(EDXA)显示球石成分中没有局部成分变化的证据。提出了一种生物控制单个放射状晶段发育的机制，即方解石菱面体的初始取向与有机基板平行，然后通过球粒体囊泡膜发育的超微结构所设置的空间限制，在三维方向上对晶体生长进行矢量调控。讨论了(1210)面离子与含多糖基板中的大分子相互作用的几何、立体化学和对称性要求。
Electron diffraction and high-resolution transmission electron microscopy indicate that the radial-segments composing coccoliths of the marine alga Emiliania huxleyi are individual single crystalline units of calcite. The top and bottom surfaces of the plate-like lower element correspond to the (1210) and (1210) faces, and the [0001] direction (c axis) is oriented parallel to these faces and in the direction of elongation of the lower and upper elements. The [1010] direction is perpendicular to the direction of elongation and corresponds to the duraction of growth of the hammer-head extension in the upper element. Each radial segment exhibits handedness when viewed from above. The peripheral edges of the lower element are truncated by (1014) and (1018) rhombohedral faces with the (1018) face being more extensively developed and always positioned to the left when viewed from above, indicating the specific growth of the (1210) face on the surface of underlying base plate. Energy-dispersive X-ray analysis (EDXA) showed no evidence for localized compositional changes in the coccolith components. A mechanism is proposed in which the biological control of the development of individual radial segments is determined by the initial orientation of calcite rhombohedra with the (1210) face parallel to teh organic base plate, followed by vectorial regulation of crystal growth in three dimensions through the spatial restrictions set by the developing ultrastructure of the surrounding coccolith vesicle membrane. The geometric, stereochemical and symmetry requirements of molecular interactions between ions in the (1210) face and macromolecules in the polysaccharide-containing base plate are discussed.