Factors Affecting Cell Divison in Plant Cells

Abstract

Tobacco BY-2 cell line has unique characteristics (Nagata et al. 1992; Shibaoka 1993). Amongst, this cell line cultured at the optimal conditions showed very fast growth rate, as it showed a doubling time of 13--14 hrs and this cell line propagated 100--120 fold in a week. As a consequence, high synchrony of ca. 70% in terms of mitotic index (MI) starting from S phase is attained after the release of aphidicolin treatment, while much higher synchrony of ca. 95% MI starting from M phase can be obtained after the release of the sequential treatment of aphidicolin and propyzamide. This high synchrony is frequently being used for the study of various issues of plant cell cycle studies. We are further seeking how the cell cycle progression of this cell line could be stopped and re-started by other procedures than those described above. Then we found that cell cycle progression could be arrested and re-started at least by two treatments. One is phosphate starvation, while the other is auxin starvation. When stationary phase tobacco BY-2 cells were cultured in a medium without phosphate for 3 days, the cell cycle progression was arrested at G0 phase. Subsequently, when phosphate was added to the medium, semi-synchronous cell division was induced. This cell division was preceded by DNA synthesis, indicating that the addition of phosphate regained the meristematic activity in the cells which were blocked at the G0 phase of the cell cycle. Under this condition, a few phosphate up-regulated genes and a down-regulated gene were identified and characterization of these genes are currently being conducted (T. Sano, T. Nagata, unpublished results).