Studies on the Growth of Tobacco Roots : VI. Effect of oxygen concentration on the mitosis of root apex

Abstract

Intact or excised tobacco root tips and tobacco anthers were incubated in various gas conditions, in order to determine the effect of exygen concentration upon the mitosis of root apex. The results obtained were as follows: 1. The mitotic index of root apex cells showed that the rate of cell division was highest at the position of the differentiation of sieve tube cells in transverse sections. 2. The optimum concentration of O2 for the cell division in root apex of the intact seedlings was around 7ppm, but in the media of 24 ppm and 1 ppm the mitosis was arrested. Furthermore, some differences in the diurnal variation of cell division was found among the concentration of O2. 3. In the air or in the gas containing l00% oxygen, the mitotic ratio of excised root tip rapidly decreased in 4 hours after the treatment, but in the atmosphere of industrial nitrogen the decrease of mitotic index was obviously retarded. Exchange of nitrogen to air accelerated cell division, and in consequence, decreased mitotic index rapidly. 4. Meiosis was quickly accomplished in oxygen, whereas in nitrogen it proceeded slowly.The auther concluded from the experiment descrived above that the exposure to oxygenlack or surplus, all have the effect of preventing cells from entering mitosis, i.e. passing from interphase into prophase, and that the former represent an arrest of the proceeding of nuclear division phase.