Hydroxyurea-induced mitotic synchronization in Allium sativum root meristems

The synchronized divisions following a treatment with hydroxyurea (HU) - an inhibitor of DNA synthesis - were studied in root meristems of Allium sativum using two methods: autoradiography of median sections and morphological labeling with a cytokinesis inhibitor. It is shown that the second wave of mitoses is heterogeneous: it is composed mostly of cells which have been synchronized in the S phase by the HU treatment, of cells coming from the quiescent center stimulated to enter DNA synthesis and of cells which were not blocked by the 23 h HU treatment (slow cycling cells). It is also shown that the cell cycle following the first synchronized division is considerably shortened by the synchronization procedure.