Mitosis and Differentiation in Roots Treated with Actinomycin.

In the presence of actinomycin D (90 microg/ml), mitosis in root meristem of Allium cepa L. ceases after a delay of 36 hours. The block occurs at interphase. Differentiation of prevascular tissue is suppressed, and the evidence suggests it begins to fail before mitosis stops. Autoradiograms of roots treated with tritiated uracil show that synthesis of ribonucleic acid is blocked after mitosis fails. The effects of the antibiotic are reversible.