Morphological Study on the Chloroplast Division of a Chromophytic Alga, Heterosigma akashiw

点击翻译按钮获取中文摘要

Summary. The plastokinesis (kinesis of chloroplast) of a raphidophyte alga, Heterosigma akashiwo was studied by electron microscopy using rapid freezing and freeze-substitution techniques. The chloroplasts are enveloped by two pairs of tightly appressed double membranes, the inner and the cytoplasmic outer pair. The inner pair constricts to divide in advance of the outer pair. By observation of serial sections and electron-opaque, annular structure (plastid dividing-ring) was observed at the isthmus of constricting chloroplasts, girdling the periplastidal outer surface of the inner pair of the four surrounding membranes. These observations suggest that the mechanism underlying the constriction of the inner and outer pair may differ from each other. The localization of the annular structure (plastid-dividing ring) suggests that the inner pair of the surrounding membranes may be homologous to the double envelope membranes of the chleroplasts of Chlorophyta and Rhodophyta. In addition these findings provide a new evidence supporting the secondary endosymbiosis hypothesis for the origin of the chleroplasts in chromophyte algae.