INFLUENCE OF HYDROXYUREA ON CELL DIVISIONS AND MICROTUBULAR CYTOSKELETON IN ALLIUM-CEPA ROOT-MERISTEM

In onion roots, hydroxyurea (HU) causes a gradual depression of mitoti c activity which ceases after 24-36 hrs. The effect is reversible; div isions begin after several hours of recovery and after 12-14 hrs about 90% cells undergo mitosis. Mitotic activity commences in the distal r egion of the apical meristem, and as a wave it spreads towards the ape x. In the roots treated with HU for a short time, the tubulin immunofl uorescence method reveals normal arrays of microtubules (MTs). After 3 6 hrs of HU treatment there are only cortical and endocytoplasmatic MT s. In the recovering roots, pre prophase bands (PB) mitotic spindles a nd phragmoplasts appear. Some PBs are split into two parallel rings. T hese abnormal PBs mostly occur in elongated cells. Apart from this, HU does not appear to have any significant influence on microtubular org anization.