Figure 4.

The duration of light exposure after infection affects the requirement for MeSA during SAR development. Immediately following 1° and 2° inoculations, 3- to 4-week-old wild-type (wt) and bsmt1-3 plants were subjected to 8, 5.5, 3.5, 1.5, and 0 h of light. The growth of virulent Pst in uninoculated, distal tissues was monitored at 2 d post 2° inoculation in plants that previously received a mock inoculation with MgCl₂ (black bars) or were infected with Psm AvrRpt2 cor⁻ (SAR induction; white bars). Means of six replicates ± sd of the combined results from two experiments are presented. Asterisks directly above each set of white/black bars indicate statistically significant differences (** P < 0.01, Student’s t test) between Pst growth in plants induced for SAR by Psm AvrRpt2 cor⁻ versus growth on mock-inoculated control plants for each genotype and duration of light exposure. Letters within the white bars indicate whether there was a statistically significant differences (P < 0.05) in Pst growth in Psm AvrRpt2 cor⁻-inoculated wild-type and bsmt1-3 plants that were subjected to different times (am and pm) of inoculation, using ANOVA and posthoc tests. Bars with the same letter indicate no significant difference, while bars with different letters indicate significantly different levels of Pst growth.