Rates of cell entrance into different periods of the cell cycle sustain that negative exponential cell age distribution occurs in Allium cepa L. meristems

The rates of cell entrance into three cell cycle periods, G sub(1), S and metaphase, have been measured in meristems of Allium cepa) L. roots. The objective was to study, in a direct way, the question of cell age distribution in a tissue formed by proliferating cells with different average generation times. Entrance rates significantly changed from one period to another: the number of cells entering into G sub(1) per unit time almost doubled the entry rate into metaphase. These data rules out a linear cell age distribution.