Enhanced nickel tolerance of endocytotic and retromer pathway mutant strains. (a) Nickel accumulation by wild-type (WT) and pathway I mutant strains (see Figure 6a). The indicated mutants were exposed to NiCl2 (1 mmol/l), treated with Newport Green, and visualized using fluorescence microscopy (see 'Materials and methods'). The percentage of fluorescent cells (average ± standard deviation of three independent experiments) is expressed relative to wild-type (WT; 100%). (b) Enhanced nickel tolerance of the Pho88 over-expressing strains. Serial dilution assays comparing the nickel tolerance of smf1Δ and pho88Δ strains transformed with the empty pYX212 vector or with the same vector bearing the SMF1 or the PHO88 coding sequences. (c) Nickel accumulation by WT and the indicated retromer-related (pathway II) mutant strains analyzed by Newport Green staining as in panel a; representative images of WT and mutant cells (100× magnification) are shown in the insets.