Figure 1.

Sulfate Induces Closure of Arabidopsis Stomata in a Dose- and Time-Dependent Manner and by Activation of NADPH Oxidases.

(A) Stomatal apertures of epidermal peels from 5-week-old soil-grown Arabidopsis wild-type plants incubated for 180 min with water containing up to 20 mM MgSO₄. The apertures of 50 stomata were determined from peels of five individual plants (n = 5). Images illustrate typical stomatal apertures in response to the treatments. The applied sulfate concentration (mM) is indicated in white in the photographs.

(B) Time course of sulfate-induced stomatal closure in detached leaves fed via the petiole with 2 mM sulfate (white, MgSO₄) or water (black, n = 50, from leaves of five individual plants).

(C) Water loss of detached leaves from 5-week-old wild-type plants that were preincubated for 180 min in water (black circles) or 2 mM MgSO₄ (white circles, sulfate).

(D) Stomatal apertures of epidermal peels treated with different nutrient salts (15 mM).

(E) Quantification of hydrogen peroxide production after fluorescent-labeling with H₂DCF-DA. Epidermal peels were treated with water (control), ABA (50 μM), or sulfate (15 mM) for 180 min before analysis (n ≥ 100).

(F) Impact of the selective NADPH-oxidase inhibitor DPI (10 μM, red dash) on ABA-induced and sulfate-induced production of hydrogen peroxide in guard cells of epidermal peels (ABA, 50 μM, sulfate, 15 mM MgSO₄ and DPI, 10 μM, n ≥ 100).

(G) Impact of NADPH-oxidase inhibition by DPI on sulfate-induced stomatal closure (n = 50, from peels of five individual plants). Bars represent mean ± sd in (A) to (E) and (G) and mean ± se in (E) and (F).

Letters indicate statistically significant differences between groups determined with one-way ANOVA (P < 0.05).