Figure 4.

Arabidopsis plants impaired in jasmonic acid (JA) and salicylic acid (SA) biosynthesis and signaling demonstrate pronounced abscisic acid (ABA)-induced stomatal closure.

Plants 3–4 weeks old were sprayed with 5 μM ABA at time 0 (marked with the arrows). Single mutants with impaired JA (a) and SA (b, c) signaling and biosynthesis, as well as double mutants (d), were studied. Time courses for stomatal conductance in the mutants and the corresponding wild-type Col-0 plants studied are shown (average ± SE, n = 6–10). Stomatal conductance is shown in relative values calculated from the data presented in Figure S7. (e) Reduction of stomatal conductance at 28 and 64 min after ABA spraying. (f) The initial rates of ABA-induced stomatal closure in npr1–1 and Col-0 were calculated as slopes of the stomatal conductance curve within 12 min after spraying with ABA. The boxes extend from the 25th to the 75th percentiles, with the horizontal lines plotted at the median values. The individual data points are shown as dots, whereas the whiskers are the minimum and maximum values (n = 6–10). Asterisks show significant differences between mutant lines and the wild type (one-way ANOVA, followed by Dunnett’s post hoc test; P < 0.05).