Webster P L, Davidson D
J Cell Biol. 1968 Nov;39(2):332-8. doi: 10.1083/jcb.39.2.332.
Treatments with tritiated thymidine (TdR-(3)H) have revealed the existence of two populations of mitotically active cells in meristems of lateral roots of Vicia faba. A rapidly dividing population, with a cycle time of 14 hr, constitutes about half the cells in the meristem. A second population of cells, with a cycle time in excess of 30 hr, is also present. Estimates of the relative size of this slowly dividing population are more difficult to make, but we calculate that this population includes 27-43% of meristem cells. The remaining fraction of the meristem is made up of cells that divide rarely or not at all. Since, at all times, both populations contribute to the mitotic index, the curve of the percentage of labeled mitoses that can be determined after a pulse label with TdR-(3)H differs from the curve expected of an ideal population in an important way: the peak value of the curve of the percentage of labeled mitoses is always less than 100%, usually between 75 and 80%. This heterogeneity within a meristem must be borne in mind in terms of the response of meristems to disruptive treatments, the mechanisms controlling mitotic cycle duration, and the spatial organization of a heterogeneous population in an organ that shows polarized growth.
用氚标记的胸腺嘧啶核苷（TdR-(3)H）进行的处理揭示了蚕豆侧根分生组织中存在两类有丝分裂活跃细胞。一类是快速分裂的细胞群体，其细胞周期为14小时，约占分生组织细胞的一半。还存在另一类细胞群体，其细胞周期超过30小时。对这个缓慢分裂群体相对大小的估计更难进行，但我们计算得出这个群体包含27% - 43%的分生组织细胞。分生组织的其余部分由很少分裂或根本不分裂的细胞组成。由于在任何时候，这两类细胞群体都对有丝分裂指数有贡献，在用TdR-(3)H进行脉冲标记后可确定的标记有丝分裂百分比曲线与理想群体预期的曲线在一个重要方面有所不同：标记有丝分裂百分比曲线的峰值总是小于100%，通常在75%到80%之间。在考虑分生组织对干扰处理的反应、控制有丝分裂周期持续时间的机制以及在表现出极性生长的器官中异质群体的空间组织时，必须牢记分生组织内的这种异质性。
