Real-time analyses of chloroplast and mitochondrial division and differences in the behavior of their dividing rings during contraction |
| |
Authors: | Shin-ya Miyagishima Ryuuichi Itoh Kyoko Toda Haruko Kuroiwa Tsuneyoshi Kuroiwa |
| |
Institution: | (1) Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan, JP;(2) Kyoritsu Women's Junior College, Kanda, Tokyo 101-0051, Japan, JP |
| |
Abstract: | The time courses of chloroplast and mitochondrial division and the morphological changes in the plastid-dividing ring (PD
ring) and mitochondrion-dividing ring (MD ring) during chloroplast and mitochondrial division were studied in Cyanidioschyzon merolae De Luca, Taddei and Varano. To accomplish this, chloroplast and cell division of living cells were continuously video-recorded
under light microscopy, and the morphological changes in the PD and MD rings were analyzed quantitatively and three-dimensionally
by transmission electron microscopy (TEM). Under the light microscope, the diameters of the chloroplast and the cell decreased
at uniform velocities, the speed depending on the temperature. To study in detail the sequential morphological change of the
mitochondrion in M phase and the contractile mechanism in the divisional planes of the chloroplast and the mitochondrion,
we observed the PD and MD rings, which are believed to promote contraction, under TEM, using the diameter of the chloroplast
as an index of the time. Three PD rings (an outer PD ring on the cytoplasmic face of the outer envelope, a middle PD ring
in the intermembrane space, and an inner PD ring on the stromal face of the inner envelope) were clearly observed, but only
the outer MD ring could be observed. The PD ring started to contract soon after it formed, while the contraction of the MD
ring did not occur immediately after formation, but was delayed until the contraction of the PD ring was almost complete.
Once the MD ring began to contract, the rate of decrease of its circumference was 4 times as high as that of the PD ring.
As the outer PD and MD rings contracted, they grew thicker and maintained a constant volume, while the thickness of the inner
PD ring did not change and its volume decreased at a constant rate with contraction. In the early stage of contraction, the
widths of the three PD rings increased in order, from the outer to the inner ring. With contraction, their widths changed
at different rates until they came to have much the same width. In cross-section, the MD ring was wider where it was next
to the chloroplast than at the opposite side, adjacent to the nucleus in the early stage of contraction. By the late stage,
the widths of the two sides became equal. In our observations, the microbody elongated along the outer MD ring and touched
the outer PD ring during contraction of the PD and MD rings. These results clearly revealed differences between the mode of
contraction of the outer, middle, and inner PD rings, and between the PD and the MD rings. They also revealed the coordinated
widening of the three PD rings, and suggested that the microbody plays a role in the contraction of the PD and MD rings.
Received: 1 July 1998 / Accepted: 1 September 1998 |
| |
Keywords: | :Cyanidioschyzon Microbody Mito-chondrion-dividing ring Organelle division Plastid-dividing ring |
本文献已被 SpringerLink 等数据库收录! |
|