A comparison of normal and cold synchronized cell divisions in Tetrahymena

Abstract

Cell division in exponentially growing cultures of Tetrahymena pyriformis was synchronized with cold shocks according to Zeuthen. The DNA and dry mass of dividing cells from both synchronous and asynchronous populations were determined by quantitative cytochemical methods. The precision of cellular and macronuclear divisions was studied by analyzing the error due to unequal distribution of DNA and dry mass to daughter cells. The following main results were obtained: 1. 1. Dividing cells obtained from synchronized populations differed from normal dividing cells by having a higher dry mass and DNA content. 2. 2. The relative composition of the cold synchronized cells, as reflected by their DNA/dry mass ratio, was abnormal being either higher or lower than normal depending on the type of cold synchronization used and the temperature at which the cells divided. 3. 3. In cold synchrony the division process is as exact as the normal division process as far as the distribution of DNA and dry mass to daughter cells is concerned. In both the normal asynchronous and in the cold synchronized populations, the distribution of DNA to daughter nuclei is markedly a less exact process than is the dry mass distribution to daughter cells.