Spore germination in Saccharomyces cerevisiae SK1 strain. (a) Schematic representation of events known to occur during spore germination in S. cerevisiae. See the text for details. (b) Budding index and heat shock resistance of germinating spores. Purified SK1 spores were prepared from a diploid strain (DS1) and suspended in YPD medium at 30°C. Samples were taken at the indicated times. Budding index (blue line) was determined by counting 100 cells under the microscope at each time point, using a hemacytometer. For heat shock analysis (red line) aliquots of this germination reaction were removed, diluted and incubated at 55°C for 12 minutes and then plated on solid rich growth medium to determine the number of colony-forming survivors. The percentage of survivors relative to the number of colony forming cells before the heat shock is plotted. (c,d) Flow cytometry analysis of germinating spores. Purified spores were prepared from a diploid strain (DS1) and suspended in YPD medium at 30°C. Samples were taken at the indicated times for FACS analysis. Haploid cells were grown in YPD medium to log phase and a sample was taken for FACS analysis. (c) Percentage of G1 cells from all cells is plotted. The red line represents the percentage of G1 cells in log phase haploids. (d) FACS profiles of germinating spores and log phase haploids.