Ilse Müller

Experiments on ageing in single cells of Saccharomyces cerevisiae

SummaryCells of Saccharomyces cerevisiae have a limited reproductive capacity.The hypothesis, that the limiting factor is the ratio of cell surface to volume, was tested in 2 experiments: The mean number of buds was determined a) in cells of different genotype but the same cell size, and b) in isogenic cells of different size (polyploid strains from 2 n to 6 n). In a) no difference was found, in b) the number of buds was highest in the 4 n cells, which have a lower surface: volume ratio than the diploid cells. These results demonstrate, that this ratio is at least not the sole determinant of life span.In a third experiment it was tested, whether the buds of young and of very old mother cells were genetically and physiologically equivalent. In no case a sign of deterioration with increasing age was detected.

A correlation between shortened life span and UV-sensitivity in some strains of Saccharomyces cerevisiae

SummaryFrom a UV-irradiated sample of diploid cells several clones were isolated, which produced cells with a shortened life span. A closer examination of three of these clones showed among other deviations from the wild type a higher sensitivity to UV-irradiation. Three other clones, which were selected from a haploid strain as UV-sensitive mutants, proved to be shortlived as well. In all these strains photoreactivation and liquid holding reactivation were unimpaired. There was no cross-sensitivity to X-irradiation. The correlation between shortened life span and UV-sensitivity is discussed.

Das somatische Mutantenspektrum vonEphestia kühniella Z. bei verschiedenen Dosen weicher 10 kV- und mittelharter 100 kV-Röntgenstrahlen sowie der harten60Co-Strahlung

Summary1.The dose-effect curves for the four somatic scale mutations ofEphestia, ES 1, 2, 3, and 4, were determined for 10 kV and 100 kV X-rays and60Co γ-rays.2.After double logarithmic transformation the relation between the dose and the mutation rate is expressed by a straight line. The regression coefficients of this line are the same within each treatment series as well as between them for all four somatic mutants.3.In all experiments the mutation rate increased in the same proportion to the dose, although each mutant had a characteristic rate. The dose does not selectively alter the mutation rate. The mutation spectrum remains the same within each series at a particular dose.4.The mutation spectra of the five experimental series showed differences greater than expected by random deviation. These variations in the mutation spectra cannot be attributed to the different wave-length of ionizing radiation here used, but rather result from unknown causes related to the fact that the experiments were not carried out concurrently.5.This investigation showed, that for the interpretation of differences in the relative frequencies of different mutants it is not allowed to compare them with a theoretical random deviation. To avoid on overestimation of small differences, it is necessary to use as a basis for the comparison, the differences between the repetitions of similar experiments.

Über Änderungen im Verlauf von Dosiseffektkurven und ihre Auswirkungen auf das Mutantenspektrum

Dose response curves of 4 somatic mutations ofEphestia kuhniella were established for the dose-range between 100 and 1000r of X-rays after six hours of pretreatment in different temperatures (+3 and +35°C). The curves are non-linear and can be fitted by the equationy=axb, werea is a constant, which is different for each mutant type, whileb is the same for all four mutants. The values ofa andb vary with the pre-irradiation-temperature. The exponentb is higher after a high temperature-treatment than after a low one. The differenceb35o-b3o is the same for all mutants. The sensitivity of the mutation process (a) goes down after the warm treatment compared to the cold one. The direction of the change is the same for all mutants, but the difference between the treatments is proportionally higher in the less frequent types (ES 2 and ES 4) than in the more frequent mutants (ES 1 and ES 3). This leads to differences in the mutational spectrum, which — at certain doses — are as pronounced as to make the different mutant types show different reactions towards the same treatment (cold treatment, for example, yields more ES 2 and less ES 1 than a warm one at doses from about 500 r up to about 1300 r).SummaryDose response curves of 4 somatic mutations ofEphestia kühniella were established for the dose-range between 100 and 1000r of X-rays after six hours of pretreatment in different temperatures (+3 and +35°C). The curves are non-linear and can be fitted by the equationy=axb, werea is a constant, which is different for each mutant type, whileb is the same for all four mutants. The values ofa andb vary with the pre-irradiation-temperature. The exponentb is higher after a high temperature-treatment than after a low one. The differenceb35o-b3o is the same for all mutants. The sensitivity of the mutation process (a) goes down after the warm treatment compared to the cold one. The direction of the change is the same for all mutants, but the difference between the treatments is proportionally higher in the less frequent types (ES 2 and ES 4) than in the more frequent mutants (ES 1 and ES 3). This leads to differences in the mutational spectrum, which — at certain doses — are as pronounced as to make the different mutant types show different reactions towards the same treatment (cold treatment, for example, yields more ES 2 and less ES 1 than a warm one at doses from about 500 r up to about 1300 r).The investigations may serve as an example for the fact, that a change in the mutational spectrum does not necessarily imply a different reaction of the mutant types to the modifying agent, but that it can be brought about as well by an analogous change in the parameters of their dose effect curves.

Über die Auslösung von somatischen Mutationen bei Ephestia kühniella Z. durch weiche und mittelharte Röntgenstrahlen (10–100 kV)

SummaryExperiments were carried out to investigate the effects of different wavelengths of X-rays (10–100 kV, 600 r) on four somatic mutations of the scales on the hind wings of Ephestia kühniella Z.We made three experiments at different times. Each consisted of eight groups for the different voltages of the X-rays.The mutation rates and the relative frequencies of the four mutations were compared.There are no correlations between the mutational spectrum and the qualities of X-rays.The variations between each group of one experiment and between the three experiments are great. It cannot be said which factors may be responsible for this variability.

[Cell volume and dry weight of homo- and heterozygous strains of Saccharomyces cerevisiae during the culture growth cycle and under different environmental conditions].

1. Es wurden Zellvolumen und Trockengewicht in stationaren Kulturen von drei diploiden Stammen von Saccharomyces cerevisiae bestimmt, die in verschiedenen Nahrmedien angezogen wurden. Es handelt sich um zwei nicht verwandte, vollstandig homozygote Stamme und ihren Bastard. In allen Fallen hat der Bastard die kleinsten Zellen. Zellen, die in einem Minimalmedium, das nur eine niedrige Teilungrate erlaubt, angezogen wurden, sind kleiner als die sich schneller teilenden Zellen im Komplettmedium. Die Stamme mit den groseren Zellen haben auch ein groseres Trockengewicht/Zelle. Dagegen spiegelt sich der Grosenunterschied zwischen den Medien nicht im Trockengewicht wider. 2. Im Laufe des Kulturwachstums andert sich das Zellvolumen bei allen Stammen in gleicher Weise: Wahrend der Lag-Phase nimmt das mittlere Volumen zu, vermutlich auf Grund des Heranwachsens einiger kleiner Zellen; wahrend der Log-Phase verringert sich das Volumen wieder. Der Bastard ist in der Log-Phase nicht kleiner als der kleinste Elter. Die Variabilitat der Zellgrose hat ein Maximum in der stationaren Phase und ein Minimum in der fruhen Log-Phase. Es wird uber die Starke der Korrelation zwischen Zellwachstum und-teilung diskutiert.Summary1.In stationary cultures of 3 diploid strains of Saccharomyces cerevisiae (2 completely homozygous ones and their hybrid) cell volume and mean dry weight were determined for growth in different media. In each case the hybrid had the smallest cells. Cells from cultures in minimal medium, where growth was slow, were smaller than cells from complete medium, where cells had a higher division rate. The dry weight per cell was higher in strains with larger cells than in those with smaller cells, but there was no corresponding difference in dry weight for the volume difference between the media.2.During the growth cycle of cultures the cell size of all 3 strains changes in a typical way: the mean volume increases during lag-phase, presumably because of the growth of some small cells to adult size. During log-phase the cells become smaller, and the hybrid is not smaller during this phase than the smallest parent. Variability of cell size is maximal during the stationary phase and minimal in early log-phase. The correlation between cell growth and cell division of discussed.Zusammenfassung1.Es wurden Zellvolumen und Trockengewicht in stationären Kulturen von drei diploiden Stämmen von Saccharomyces cerevisiae bestimmt, die in verschiedenen Nährmedien angezogen wurden. Es handelt sich um zwei nicht verwandte, vollständig homozygote Stämme und ihren Bastard. In allen Fällen hat der Bastard die kleinsten Zellen. Zellen, die in einem Minimalmedium, das nur eine niedrige Teilungrate erlaubt, angezogen wurden, sind kleiner als die sich schneller teilenden Zellen im Komplettmedium. Die Stämme mit den größeren Zellen haben auch ein größeres Trockengewicht/Zelle. Dagegen spiegelt sich der Größenunterschied zwischen den Medien nicht im Trockengewicht wider.2.Im Laufe des Kulturwachstums ändert sich das Zellvolumen bei allen Stämmen in gleicher Weise: Während der Lag-Phase nimmt das mittlere Volumen zu, vermutlich auf Grund des Heranwachsens einiger kleiner Zellen; während der Log-Phase verringert sich das Volumen wieder. Der Bastard ist in der Log-Phase nicht kleiner als der kleinste Elter. Die Variabilität der Zellgröße hat ein Maximum in der stationären Phase und ein Minimum in der frühen Log-Phase. Es wird über die Stärke der Korrelation zwischen Zellwachstum und-teilung diskutiert.

Die Abhängigkeit des somatischen Mutantenspektrums vonEphestia kühniella vom Entwicklungsstadium der bestrahlten Tiere

SummaryMüller (1963) suggested that the differences which were found in the dose effect curves of 4 somatic mutations, affecting scale form and colour, after 6 hrs pretreatment in low and high temperatures, might be due to the fact that the pupae were x-rayed at 2 different developmental stages, each of which exhibiting a different sensitivity pattern for the 4 mutant types. In order to test this suggestion, dose effect curves were established for pupae of the 2 age groups corre-sponding to the stages which were attained by the temperature treatments.The exponent of the dose effect curves is the same for all mutant types and independent of the age at irradiation. The age groups differ in their mutational spectra: The older pupae show significantly more mutants of type ES 1 and less of type ES 2 than the younger group. Both groups have identical frequencies of ES 3, and the differences between the ES 4 — frequencies, which lie in the same direction as those of ES 2, are not significant. The results are discussed with regard to a possible difference in the specific radiosensitivity of epithelial cells and scalestem-cells I.