One hundred-milliliter cultures of Xanthomonas campestris strains were grown overnight in peptone, yeast, and malt extract medium. Bacteria were centrifuged for 30 min at 6,000g. The supernatant was transferred to a new centrifuge bottle and centrifuged for 90 min at 20,000g. The supernatant was transferred to 50-mL Falcon tubes and was extracted with one-third volume of ethyl acetate. Phases were separated by centrifugation for 15 min at 13,000g. The organic phase was evaporated using a Speedvac concentrator and was resuspended in 500 μL of water. For stomatal bioassays, 6 μL of extracts were used for every milliliter of incubation buffer.