Aged mother cells of Saccharomyces cerevisiae show markers of oxidative stress and apoptosis

Recently, we and others have shown that genetic and environmental changes t hat increase the load of yeast cells with reactive oxygen species (ROS) lea d to a shortening of the life span of yeast mother cells. Deletions of yeas t genes coding for the superoxide dismutases or the catalases, as well as c hanges in atmospheric oxygen concentration, considerably shortened the life span. The presence of the physiological antioxidant glutathione, on the ot her hand, increased the life span of yeast cells. Taken together, these res ults pointed to a role for oxygen in the yeast ageing process. Here, we sho w by staining with dihydrorhodamine that old yeast mother cells isolated by elutriation, but not young cells, contain ROS that are localized in the mi tochondria. A relatively large proportion of the old mother cells shows phe notypic markers of yeast apoptosis, i.e. TUNEL (TdT-mediated dUTP nick end labelling) and annexin V staining. Although it has been shown previously th at apoptosis in yeast can be induced by a cdc48 allele, by expressing pro-a poptotic human cDNAs or by stressing the cells with hydrogen peroxide, we a re now showing a physiological role for apoptosis in unstressed but aged wi ld-type yeast mother cells.