VOLUME GROWTH OF DAUGHTER AND PARENT CELLS DURING THE CELL-CYCLE OF SACCHAROMYCES-CEREVISIAE A ALPHA AS DETERMINED BY IMAGE CYTOMETRY/

The pattern of volume growth of Saccharomyces cerevisiae a/alpha was d etermined by image cytometry for daughter cells and consecutive cycles of parent cells. An image analysis program was specially developed to measure separately the volume of bud and mother cell parts and to qua ntify the number of bud scars on each parent cell. All volumetric data and cell attributes (budding state, number of scars) were stored in s uch a way that separate volume distributions of cells or cell parts wi th any combination of properties-for instance, buds present on mothers with two scars or cells without scars (i.e., daughter cells) and with out buds-could be obtained. By a new method called intersection analys is, the average volumes of daughter and parent cells at birth and at d ivision could be determined for a steady-state population. These volum es compared well with those directly measured from cells synchronized by centrifugal elutriation. During synchronous growth of daughter cell s, the pattern of volume increase appeared to be largely exponential. However, after bud emergence, larger volumes than those predicted by a continuous exponential increase were obtained, which confirms the rep orted decrease in buoyant density. The cycle times calculated from the steady-state population by applying the age distribution equation dev iated from those directly obtained from the synchronized culture, prob ably because of inadequate scoring of bud scars. Therefore, for the co nstruction of a volume-time diagram, we used volume measurements obtai ned from the steady-state population and cycle times obtained from the synchronized population. The diagram shows that after bud emergence, mother cell parts continue to grow at a smaller rate, increasing about 10% in volume during the budding period. Second-generation daughter c ells, i.e., cells born from parents left with two scars, were signific antly smaller than first-generation daughter cells. Second- and third- generation parent cells showed a decreased volume growth rate and a sh orter budding period than that of daughter cells.