Effect of EBR treatment on basal thermotolerance of Arabidopsis WT and SA, ET, JA and ABA mutant seedlings. (A and B) WT and mutant seedlings grown on a nutrient medium in the absence (C) or presence of 1 μM EBR (E) were exposed to 43°C for 4 h. Photographs of the seedlings were taken after recovery at 22°C for 7 days. (C-F) Proportion of WT and mutant seedlings surviving the lethal heat stress (43°C for 4 h). Seedlings grown and treated as described in methods were scored as dead or surviving after 7 days of recovery at 22°C. WT controls were Ler for abi1-1 and aba 1-1, Col-6 for aos, and Col for all other mutants. Data shown are average of three replicates. Error bars represent standard error (SE) of mean for three replicates. Asterisks above the histograms indicate the significance of differences between untreated and EBR-treated genotypes as analyzed by Student's t-test (**p < 0.01; *p < 0.05).