Colonies were scored after a 48-h incubation at 28 °C. In antioxidant protection tests, a reactive oxygen species (ROS) scavenger viz. 1.0 M glycerol learn more or 10 mM pyruvate (Patikarnmonthon et al., 2010) was added to bacterial cultures 10 min before heat treatment. All experiments were repeated independently three times. The exponential cultures of X. campestris pv. campestris wild-type and katA-katG double-mutant strains (Jittawuttipoka et al., 2009) were subjected to heat shock at 37 °C for 15 min. Cells were collected by centrifugation at 5000 g for 10 min for total RNA preparation. RT-PCR was carried out to synthesize cDNA as described

previously (Jittawuttipoka et al., 2010). Reverse transcription reaction was performed using 5 μg total RNA, the

RevertAid™ M-MuLV Reverse transcriptase Kit (Fermentas), and random hexamers according to the manufacturer’s recommendation. The specific primer pairs for heat shock genes were BT3194 (5′CCACCAAGGGTGAAGTCG3′)-BT3195 (5′CGCAGCACCTTGTACTCG3′) for groES, BT3190 (5′ATGGCGAGAAGCAGTTCG3′)-BT3191 (5′CGAGGTCGACAGCTCGAT3′) for dnaK, and BT3188 (5′AGCACTACGGCGAAGACG3′)-BT3189 (5′GTCGCGGTGGTACAGGTC3′) Doxorubicin for hptG. The primer pair for the 16S rRNA gene, which was used as the normalizing gene, was BT2781 (5′GCCCGCACAAGCGGTGGAG3′)-BT2782 (5′ACGTCATCCCCACCTTCCT3′). Real-time PCR was conducted using 20 ng cDNA, a specific primer pair, and SYBR® green PCR Master Mix (Applied Biosystems), and run on an Applied Biosystems StepOne Plus under the following conditions: denaturation at 95 °C for 30 s, annealing at 60 °C for 30 s, and extension at 72 °C for 30 s, for 40 cycles. To monitor the level of the katA transcript old in the ahpC mutant and the wild-type strains, the ahpC-specific primers BT2684 (5′CGCAGCGTCTCGGTGACG3′)-BT2685 (5′AGTGGAAGACGCCGCTGA3′) were used in the real-time RT-PCR reactions under the following conditions: 40 cycles of denaturation

at 95 °C for 30 s, annealing at 55 °C for 20 s, and extension at 72 °C for 30 s. Relative expression analysis was carried out using stepone software v2.1 and expressed as folds of expression relative to the level of an X. campestris pv. campestris wild type grown under untreated conditions. Experiments were repeated independently three times. Flow cytometric analysis was performed as described previously (Fuangthong et al., 2011). Exponential-phase cultures of X. campestris pv. campestris were washed twice with a phosphate-buffer saline (PBS) solution and resuspended in PBS to yield a cell density of 104 cell mL−1. The cell suspension (500 μL) was mixed with 1 μL of 2 mg mL−1 dihydrorhodamine-123 (DHR) (Molecular Probe) before heat treatment for at 45 °C for 2 min.