CELL PHISIOLOGICAL AND MOLECULAR BIOLOGICA STUDIES ON THE DIVIDING APPARATUS OF PLASTIDS AND MITOCHONDRIA

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Plastidokinesis makes use of organelle dividing apparatuses such as plastid-dividing ring (PD ring) and mitochondrion-dividing ring (MD ring). The plastid-dividing apparatus (PD apparatus) is composed of three electron-dense rings (the outer, middle and inner), while the mitochondrion-dividing apparatus (MD apparatus) is triple electron-dense rings in cytoplasm, inter-space between inner and outer envelopes and inner ring in the mitochondrial matrix.The behaviors of both the PD and MD apparatuses throughout organelle division in Cyanidioschyzon merolae has been revealed in detail by electron microscopy. When cells enter mitosis, the inner PD ring forms first, followed by the outer and middle rings and finally the MD rings. The PD rings begin to contract before the MD rings. However, the MD rings start to contract at about 4 times the speed of the PD rings and catch up to the PD rings. The cross-sectional areas of both the outer PD and MD rings increase as contraction in the plane of division progress. This suggests that the outer rings of organelle dividing apparatuses (OD apparatus) provide the motive forse for contractian. Recently the dividing chloroplasts with a PD ring have been isolated from the cells and it is essential for isolation of the intact PD ring and identification of proteins in the PD ring. The FtsZ genes of both mitochondrial and plastid types were isolated from the cell and their antibodies were obtained from mouse. Immuno-electron microscopy using their antibodies showed that the FtsZ proteins were not located on the PD ring and the MD ring, respectively.