Ultrastructural observations of the isthmus of dividing chloroplasts

点击翻译按钮获取中文摘要

Ultrastructure of the isthmus of constricting chloroplasts of a green alga Closterium ehrenbergii was three-dimensionally observed by transparent electron microscopy of serial sections. The isthmus was encircled outside (cytoplasmic side) by a large number of concentrically orientated electron-opaque fibrous structures. Three-dimensional reconstruction showed that these structures as a whole form belts turning around the isthmus several times. This type of the distribution of electron-opaque fibrous structures around the isthmus of the dividing chloroplasts is quite different from those described for the other plants. No electron-opaque ring-like structures were detected on the stromal surface of the inner envelope membrane as observed in higher plants. Microtubule inhibitor amiprophos methyl (APM) which was observed not to inhibit plastokinesis (Hashimoto, 1992) did not disrupt the electron-opaque fibrous structures, indicating the structures be not relevant with microtubules. The ring-like distribution of the electron-opaque fibrous structure apparently coincide with the observation that the isthmus region of the dividing chloroplast was stained with rhodamine-conjugated phalloidin.Endoplasmic reticulum (ER) covers almost all over the surface of 'interphase' chloroplasts. When the chloroplast entered division phase, ER was separated at the isthmus region of the dividing chloroplast. As chloroplasts constricted. daughter nuclei moved into the groove the chloroplasts. Such nuclear migration was suggested to be driven by a rodshaped microtubule center. These observations suggest that in Closterium the cycle of chloroplast division and other organelles may be cooperatively regulated.