Figure 2.

Whole-vacuole recordings of Glc-triggered proton currents in mesophyll vacuoles of wild-type (Wt) and TMT mutant plants. A, The cartoon shows the experimental conditions at pH 5.5 in the vacuolar lumen (pipette) and pH 7.5 in the cytosol (bath) in the absence (left) and presence (right) of 50 mm Glc. Representative current traces recorded from vacuoles of wild-type, TMT1-overexpressing line 4 (35S:tmt1;1-2), and tmt1-2::tDNA plants are given below the cartoon. Cytosolic Glc treatment indicated by the superimposed gray bars resulted in downward deflection of the current trace. B, Sugar-induced changes in current density determined from individual vacuoles under conditions identical to those in A are given as means ± se. Number of experiments was n = 14 for wild-type (gray bar), n = 12 for the TMT1-overexpressing line 4 (striped bar), and n = 9 for tmt1-2::tDNA (white bar) vacuoles. Data comprise Glc-induced current responses from vacuoles isolated from leaves without and with preincubation in 100 mm Glc. Note that similar Glc-induced current densities were recorded under different Glc preconditions (data not shown). C, pH dependence of Glc-triggered proton currents in mesophyll vacuoles of TMT1-overexpressing line 4. Representative current traces recorded at pH 7.5 in the cytosol and either pH 7.5 or 5.5 in the lumen are shown. Cytosolic Glc treatment (50 mm) is indicated by the superimposed gray bars. Current responses were obtained from vacuoles isolated from leaves without Glc preincubation. Average Glc-induced current densities ± se determined under symmetrical and asymmetrical pH conditions are given below the individual current recordings. Number of experiments was n = 6 for pH 5.5 and n = 8 for pH 7.5 in the vacuolar lumen.