Cell cycle synchronization in the root meristem of Allium cepa L.

A high level of cell cycle synchronization in Allium cepa was achieved using a 24 h hydroxyurea block (1.25 mM) followed by 20 h of recovery (without hydroxyurea) and a subsequent 4 h treatment with saturated α-bromonaphthalene solution. This procedure was very effective in producing a synchronously dividing cell population with a 76% mean mitotic index and a 30% frequency of metaphase stages. After release from hydroxyurea arrest, large fractions of cells synchronously entered successive phases: G1, S, and G2. The calculated duration of the cell cycle, 13 h, is in general accordance with previous reports. A detailed protocol for obtaining a high mitotic index and a large portion of cells in a particular cycle phase (G1, S, G2) was prepared.