Chemistry Reference
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Figure 2.
Coccolithogenesis in
Pleurochrysis carterae.
Schematic section, based on TEM images,
through a coccolithophore showing coccolith formation within Golgi-derived vesicles. Reproduced with
permission from van der Wal et al. 1983.
cisternae, derived from the Golgi body. The process commences with formation of an
organic scale. These scales have a distinctive microfibrillar ultrastructure that is
characteristic of scales in the haptophytes, and homologous non-calcified scales occur in
most non-coccolithophorid haptophytes (e.g.
,
Billard 1994). In some cases, the scales are
exocytosed without further development, to form an inner layer of body scales. In others,
the vesicle develops a rather complex form, with extensions containing dense particles
termed coccolithosomes. Nucleation of calcite then occurs around the periphery of the
base-plate scale followed by crystal growth upward and outward to form the complete
coccolith. During coccolith growth, the vesicle gradually expands, remaining in rather
close contact with the developing coccolith. After completion of the coccolith, the vesicle
dilates and at this stage, a dense organic coating is visible around and between the
coccolith crystals. Exocytosis then occurs, apparently by fusion of the vesicle membrane
and cell membrane. In this species the coccolithosomes appear to play a key role in
