These diagrams summarize the rearrangements of the chloroplast during the cell cycle in Sellaphora. Each picture is an equal-area projection of the cell periphery - as if the cell were stretched out flat laterally. The central ellipse is the epivalve and this is flanked by two curved strips representing the two sides of the girdle. In order to show the hypovalve adequately, the half shown on the right is duplicated on the left (beyond the dashed line). The mapping is summarized in a separate diagram.
During interphase (I) the H- shaped chloroplast lies against the epivalve.
In preparation for mitosis (II), the chloroplast moves onto girdle (essentially a translational movement).
During mitosis (III), the chloroplast lies with its major constriction lying along the mid-line of the girdle. This constriction deepens and cuts the chloroplast in two, just before cytokinesis. The distal side of the chloroplast, lying on the opposite side of the chloroplast, develops a wide invagination. At cytokinesis (IV), the invagination is deep, almost reaching the centre of the epivalve.
After cytokinesis and during valve formation (V), a second indentation of the chloroplast begins to develop on the opposite side from the first.
On completion of the new valve (VI), the chloroplast rotates clockwise (as seen from the cell exterior) through 90º and the second invagination continues to deepen.
In newly separated cells (VII), the chloroplasts are often still slightly asymmetrical, reflecting the asynchronous development of the two invaginations.
The chloroplast invaginations that develop during mitosis and early interphase represent the first phase of chloroplast division, but division arrests at a late stage and is not completed until just before the next cell division. Similar arrest is seen also in some Caloneis and Lyrella species.
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