Convergent lifespan reaction norms in the yeast cultures exposed to different environmental stresses

Lifespan extension under mild stress is frequently observed although difficult to quantify and generalize as previous studies differed substantially in specific experimental arrangements. We cultured the budding yeast in several environments defined by different temperature, source of energy, saline concentration or combinations of these factors. Cells obtained under different growth regimes were transferred to identical and generally nonstressful conditions except for an absence of organic carbon. Chronological lifespan (CL) of the starving cells showed an approximately common norm of reaction when plotted against the growth rate which served as a measure of stress intensity. CL increased roughly 50% in cultures raised at moderately slower pace, regardless of what particular single or multiple stress signals were present, and then decreased gradually with a deepening growth deceleration. We suggest that the strongly nonlinear relation between the metabolic rate and longevity can be a potent constraint controlling norms of phenotypic reaction in a variety of environmental gradients