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ROLE OF MULTIPLE FTSZ RINGS IN CHLOROPLAST DIVISION UNDER OLIGOTROPHIC AND EUTROPHIC CONDITIONS IN THE UNICELLULAR GREEN ALGA NANNOCHLORIS BACILLARIS (CHLOROPHYTA, TREBOUXIOPHYCEAE)1
Article first published online: 23 JUL 2012
© 2012 Phycological Society of America
Journal of Phycology
Volume 48, Issue 5, pages 1187–1196, October 2012
How to Cite
Sumiya, N., Owari, S., Watanabe, K. and Kawano, S. (2012), ROLE OF MULTIPLE FTSZ RINGS IN CHLOROPLAST DIVISION UNDER OLIGOTROPHIC AND EUTROPHIC CONDITIONS IN THE UNICELLULAR GREEN ALGA NANNOCHLORIS BACILLARIS (CHLOROPHYTA, TREBOUXIOPHYCEAE). Journal of Phycology, 48: 1187–1196. doi: 10.1111/j.1529-8817.2012.01204.x
Received 29 August 2011. Accepted 13 June 2012.
- Issue published online: 4 OCT 2012
- Article first published online: 23 JUL 2012
- Accepted manuscript online: 21 JUN 2012 12:23PM EST
- chloroplast division;
- chloroplast DNA synthesis;
- chloroplast nucleoid;
- FtsZ ring;
- Nannochloris bacillaris
Chloroplasts of the unicellular green alga Nannochloris bacillaris Naumann cultured under nutrient-enriched conditions have multiple rings of FtsZ, a prokaryote-derived chloroplast division protein. We previously reported that synthesis of excess chloroplast DNA and formation of multiple FtsZ rings occur simultaneously. To clarify the role of multiple FtsZ rings in chloroplast division, we investigated chloroplast DNA synthesis and ring formation in cells cultured under various culture conditions. Cells transferred from a nutrient-enriched medium to an inorganic medium in the light showed a drop in cell division rate, a reduction in chloroplast DNA content, and changes in the shape of chloroplast nucleoids as cells divided. We then examined DNA synthesis by immunodetecting BrdU incorporated into DNA strands using the anti-BrdU antibody. BrdU-labeled nuclei were clearly observed in cells 48 h after transfer into the inorganic medium, while only weak punctate signals were visible in the chloroplasts. In parallel, the number of FtsZ rings decreased from 6 to only 1. When the cells were transferred from an inorganic medium to a nutrient-enriched medium, the number of cells increased only slightly in the first 12 h after transfer; after this time, however, they started to divide more quickly and increased exponentially. Chloroplast nucleoids changed from punctate to rod-like structures, and active chloroplast DNA synthesis and FtsZ ring formation were observed. On the basis of our results, we conclude that multiple FtsZ ring assembly and chloroplast DNA duplication under nutrient-rich conditions facilitate chloroplast division after transfer to oligotrophic conditions without further duplication of chloroplast DNA and formation of new FtsZ rings.