Biohistory journal, Winter, 2006Research
The cell walls of Trebouxiophyceae generate a diversity
of cellular division
An enlargement
An electron microscope photo of the binary division type Nanochloris during division
Even after division, it can be seen that the mother cell wall does not become detached but adheres. An enlarged photo is on the right. Those areas that have become thicker are where the Mother cell wall has overlapped.
Stichococcus becoming multicellular
With the binary dividing Stichococcus, after division the mother cell wall does not become detached but adheres in sequence to the Mother cell, daughter cell, and other progeny cells, becoming multicellular.
The Trebouxiophyceae family are unicellular algae that live in such close environments as rivers, lakes, and block walls. They have many means for cell division, and in addition to endospore formation, they have binary division, like bacteria, and the budding type, like yeast. The binary division type and the budding type are closely related in phylogenetic tree based on actine, which creates a constriction, and the DNA sequence of the 18SrRNA gene that all living creatures have. This is located at the end of the phylogenetic tree. Binary division and budding division, which are seen primordially, have branched off from endospore formation.
Examination using a microscope permits the observation that with all types of division, cytoplasmic division and the mother cell wall cleavage occur in the same way. The difference is that with binary division and budding division, there is no separation from the daughter cell after the mother cell wall cleavage. If the mother cell wall is not discarded, it is possible for the mother cell, the daughter cell, and the granddaughter cells to become linked beyond generations. It is also possible for them to become multicellular. In fact, with the binary dividing Stichococcus, the cells become linked in one row and appear multicellular. It might be that among the Trebouxiophyceae family there are some members that are taking the first step toward becoming multicellular. We hope to use observation of the cell walls to consider the significance of the diversity of cellular division and its evolution.
Dr. Yamamoto received a Ph.D. from the University of Tokyo's School of Science. She has served as an associate professor at the same university's Graduate School of Frontier Sciences and a special research fellow at the Japan Society for the Promotion of Science. She has been a professor at Senshu University since 2006.
Shigeyuki Kawano
After graduating with a degree in science from Okayama University in 1975, Dr. Kawano served as an engineering official and assistant at the National Institute for Basic Biology. He was named a teaching assistant and associate professor at the University of Tokyo in 1988, and a professor at that university's Graduate School of Frontier Sciences in 1999.
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