FIG 4 .

Changes in leaf pH in microaerophilic conditions. The pH of detached leaves inoculated with WT P. carotovorum subsp. carotovorum or the P. carotovorum subsp. carotovorum budB mutant and/or S. enterica was determined spectrophotometrically every 24 h for 96 h (A to D). The pH of leaf tissue inoculated with WT P. carotovorum subsp. carotovorum increases toward neutral over time, but this increase was diminished in the presence of S. enterica. Though there was a pH increase in the P. carotovorum subsp. carotovorum budB mutant-inoculated leaves at 24 hpi and 48 hpi (A and B, respectively), the leaf tissue acidified and resembled the water-inoculated control at 72 hpi and 96 hpi (C and D, respectively). At 96 hpi, the pH of leaf tissue inoculated with S. enterica was lower than that of the water-inoculated control, presumably due to accumulation of acids produced in anaerobic conditions (D). Data shown are the averages of five experiments. Vertical bars indicate the standard errors.