Figure 4. Sod2p Is Upregulated Specifically in Stationary Phase in tor1 Null Cells and Contributes to Stress Resistance, but Not to Life-Span Extension.
(A) Western blot analysis of Sod2p levels in wild-type and tor1 null cells at day 1 and day 2 of stationary phase. Shown at top is a pair of representative samples, and shown below is quantification of Sod2p relative to actin from three biological replicates.
(B) ROS levels of wild-type and tor1 null cells at day 1 postinoculation, measured with the ROS-sensitive fluorescent dye dihydroethidium (DHE) and flow cytometry. The y axis shows the number of cells measured at a given point on the x axis, which is a logarithmic scale of arbitrary fluorescence units. The black line represents the fluorescence profile of the wild-type strain, and the filled gray curve represents that of the tor1 null strain.
(C) Serial 10-fold dilutions of wild-type and tor1 null cells treated with the indicated levels of hydrogen peroxide (H2O2) at either day 1 or day 2 of stationary phase.
(D) Life-span curves of sod2 mutants (closed squares), tor1 sod2 double mutants (closed circles), and tor1 sod2 double mutants transformed with a plasmid bearing wild-type SOD2 (open circles) compared to appropriate empty-vector control strains.