Arrest of mitosis in roots by oxygen-lack or cyanide

Excised pea-root tips were incubated in various conditions, in order to determine the effect upon mitosis. In air the mitotic index rapidly decreased, but in an atmosphere of oxygen-free nitrogen (containing less than 0$\cdot $001% oxygen) mitotic figures persisted for up to 24 h. Counts of the total number of cells showed that the persistence of mitotic figures represented an arrest of mitosis by anaerobiosis, and not a continuation of cell division as had previously been surmized. The effects of oxygen-lack were simulated by 10$^{-2}$ M-sodium cyanide. Mitotic arrest persisted for only about 4 h if industrial nitrogen (containing about 0$\cdot $05% oxygen) was used, or if 10$^{-3}$ M-cyanide was employed. The cells thus partially arrested slowly continued the normal course of mitosis, and did not merely revert directly to interphase. Similar results were obtained with different kinds of roots, and with intact seedlings. The results were in accordance with an hypothesis that all stages of cell division depend upon the presence of oxygen, but that the visible stages of mitosis are less dependent than is the stage of entering mitosis.