ULTRASTRUCTURE OF A CHAIN‐FORMING DIATOM PHAEODACTYLUM TRICORNUTUM1

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Abstract
The ultrastructure of a chain‐forming clone of the polymorphic diatom Phaeodactylum tricornutum Bohlin has been studied by scanning and transmission electron microscopy. Both fusiform and tri‐radiate cells are capable of forming chains. The cells, lacking any silica shell, are attached to each other at the central region of the theca, leaving the arms free. Neither homogenization nor sonication completely disrupts the chains. The attachment is due to fusion of the cell wall in the central region of the cell during cell wall deposition. This fusion results from failure of the cytoplasmic cleavage furrow to separate the plasma membranes of the two daughter cells sufficiently so that a single wall is deposited instead of two separate walls. Possible explanations for this are discussed.