title: Chronological transition of mitochondrial morphology in Chlamydomonas reinhardtii (Chlorophyceae) poststationary phase growth(1).
abstract: In Chlamydomonas reinhardtii P. A. Dangeard, mitochondrial morphology has been observed during asexual cell division cycle, gamete and zygote formation, zygote maturation, and meiotic stages. However, the chronological transition of mitochondrial morphology after the stationary phase of vegetative growth, defined as the poststationary phase, remains unknown. Here, we examined the mitochondrial morphology in cells cultured for 4 months on agar plates to study mitochondrial dynamics in the poststationary phase. Fluorescence microscopy showed that the intricate thread-like structure of mitochondria gradually changed into a granular structure via fragmentation after the stationary phase in cultures of about 1 week of age. The number of mitochondrial nucleoids decreased from about 30 per cell at 1 week to about five per cell after 4 months of culture. The mitochondrial oxygen consumption decreased exponentially, but the mitochondria retained their membrane potential. The total quantity of mitochondrial DNA (mtDNA) of cells at 4 months decreased to 20% of that at 1 week. However, the mitochondrial genomic DNA length was unchanged, as intermediate lengths were not detected. In cells in which the total mtDNA amount was reduced artificially to 16% after treatment with 5-fluoro-2-deoxyuridine (FdUrd) for 1 week, the mitochondria remained as thread-like structures. The oxygen consumption rate of these cells corresponded to that of untreated cells at 1 week of culture. This suggests that a decrease in mtDNA does not directly induce the fragmentation of mitochondria. The results suggest that during the late poststationary phase, mitochondria converge to a minimum unit of a granular structure with a mitochondrial nucleoid.
authors.affiliation: Center of Molecular Biosciences, Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan.|Laboratory of Cell and Functional Biology, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Aoyama
authors.affiliation: Initiative Research Unit, College of Science, Rikkyo University, Nishi-Ikebukuro, Tokyo, 171-8501, Japan.
authors.forename: Tsuneyoshi
authors.initials: T
authors.lastname: Kuroiwa
authors.affiliation: Laboratory of Cell and Functional Biology, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa, 903-0213, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Nakamura
keywords: Chlamydomonas reinhardtii; long-term culture; mitochondrial DNA; mitochondrial fragmentation; mitochondrial morphology; poststationary phase