INCREASE IN CELL SIZE AS A MEASURE OF GROWTH OF SACCHAROMYCES CEREVISIAE

The increase in the length of the major axis of daughter cells as a measure of cell growth was re-examined with special reference to the nuclear behavior, employing a diploid strain of Saccharomyces cerevisiae. The increase in cell size in a cell cycle proceeded in a similar manner either in the synchronous culture or in the single-cell culture as a number of investigators described. Newly established facts concerning the size of daughter cells in a growth process are as follows: The newborn daughter cells had a rather uniform size under definite conditions regardless of the size of their mother cells. The heterogeneity in the cell size was mainly due to its divisional age; the cell increased in size with every budding, and the difference in cell size between age 0 and age 1 was the most prominent. The newborn daughter cells initiated budding some time after the mother cell had initiated budding, during which time the size of daughter cells generally increased. Shape of the bud varied gradually during the growth process. The bud- initial was cylindrical and then gradually became the prolate spheroidal form.Nuclear events such as DNA synthesis and nuclear migration proceeded also in a similar manner as others described. The daughter cells exhibiting migrating nucleus in the Giemsa-stained preparations showed extraordinary uniformity in size distribution. This shows that the migration of nucleus is a very rapid process; it may proceed within a period of 0.1 generation and the cell size at the time of nuclear migration was estimated to be about the fraction of 0.8 of its full size.