A flood-inoculation method that we have previously developed to infect the cotyledonary leaves of tomato [15 (link)] was modified to develop an Arabidopsis seedling flood-inoculation technique with reproducible disease symptoms. To perform uniform inoculation, 40 ml of bacterial suspension made in sterile distilled H2O containing 0.025% Silwet L-77 (OSI Specialties Inc., Danbury, CT, U.S.A.) was dispensed into the plate containing 2-week-old Arabidopsis seedlings, and the plates were incubated for 2-3 min at room temperature. After the bacterial suspension was removed by decantation, plates containing inoculated plants were sealed with 3 M Micropore 2.5 cm surgical tape (3 M, St. Paul, MN, U.S.A.) and incubated at 24°C with a light intensity of 150-200 μE m-2 sec-1 and a 12 h light/12 h dark photoperiod. Symptom development was observed at 1 and 3 dpi. In each experiment, 16 plants were evaluated, and each experiment was repeated at least three times.
To determine the bacterial growth in Arabidopsis leaves, we measured internal bacterial population at several time points (0, 1, 2, 3 and 4 dpi). Internal bacterial populations were evaluated from four biological replicates and each replicate represented a pooled sample of four independent seedlings from a single experiment grown in a single Petri-dish. Inoculated seedlings were collected by cutting the hypocotyls to separate the above agar parts (whole rosette) from the Phytagel plate, and the total weight of inoculated seedlings was measured. After measurement of the seedlings' weight, the seedlings were surface-sterilized with 5% H2O2 for 3 min. After washing three times with sterile distilled water, a pooled sample of four seedling were homogenized in 10 mL sterile distilled water using a mortar and pestle, and diluted samples were plated onto MG or LB medium containing the appropriate antibiotics. Two days after plating of diluted samples, the bacterial colony forming units (CFU) were counted using proper diluted samples. The CFU was normalized as CFU/mg using total weight of inoculated seedlings. Bacterial populations were evaluated in three independent experiments.
To determine the bacterial growth in Arabidopsis leaves, we measured internal bacterial population at several time points (0, 1, 2, 3 and 4 dpi). Internal bacterial populations were evaluated from four biological replicates and each replicate represented a pooled sample of four independent seedlings from a single experiment grown in a single Petri-dish. Inoculated seedlings were collected by cutting the hypocotyls to separate the above agar parts (whole rosette) from the Phytagel plate, and the total weight of inoculated seedlings was measured. After measurement of the seedlings' weight, the seedlings were surface-sterilized with 5% H2O2 for 3 min. After washing three times with sterile distilled water, a pooled sample of four seedling were homogenized in 10 mL sterile distilled water using a mortar and pestle, and diluted samples were plated onto MG or LB medium containing the appropriate antibiotics. Two days after plating of diluted samples, the bacterial colony forming units (CFU) were counted using proper diluted samples. The CFU was normalized as CFU/mg using total weight of inoculated seedlings. Bacterial populations were evaluated in three independent experiments.
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