Figure 1.

Effects of UVA Radiation on Stomatal Opening and δ-FlincG Fluorescence

(A) UVA radiation inhibits blue- and red-light-induced stomatal opening. Isolated Arabidopsis epidermis were illuminated with a combination of 10 μmol m⁻² s⁻¹ blue (λmax = 470 nm) and 50 μmol m⁻² s⁻¹ red (λmax = 660 nm) light in the presence or absence of 10 μmol m⁻¹ s⁻¹ UVA (λmax = 380 nm) in 10 mM MES/KOH, 50 mM KCl, pH 6.15. Stomatal apertures were measured after 3 h and 6 h illumination. Data represent means (+/− SEM) of 90 stomatal aperture measurements from three replicates. Statistical analyses were performed by one-way ANOVA with Tukey post hoc analysis, and letters show significant differences at p < 0.05.

(B) A representative graph (n = 50) of the reversible decrease of δ-FlincG fluorescence observed in mesophyll protoplasts when illuminated with 10 μmol m⁻¹ s⁻¹ UVA (λmax = 380 nm). In the presence of UVA, the fluorescence decreases within seconds and reaches a plateau. In the absence of UVA, the fluorescence rapidly returns to its initial level. The lines labeled 380 nm represent the length of time the protoplasts were illuminated with UVA.

(C) A representative measurement (n = 5) of δ-FlincG fluorescence from a guard cell on an isolated epidermal strip illuminated with UVA radiation (10 μmol m⁻¹ s⁻¹ [λmax = 380 nm]). The line labeled 380 nm represents the length of time the epidermal strip was illuminated with UVA.

(D) Effect of light quality on δ-FlincG fluorescence. Fluorescence of mesophyll protoplasts from plant expressing δ-FlincG was measured when illuminated with UVA (λmax = 380 nm, 10 μmol m⁻¹ s⁻¹), blue (λmax = 470 nm, 20 μmol m⁻¹ s⁻¹), red (λmax = 680 nm, 15 μmol m⁻¹ s⁻¹) or far-red (λmax = 730 nm, 5 μmol m⁻¹ s⁻¹) light. Far-red and red light did not have a significant effect on the fluorescence levels. UVA decreases the fluorescence by 15%, and blue increases it by 2.5% (n = 3, p < 0.05). The lines represent the length of time the protoplasts were illuminated with UVA, far-red (FR), red (R), UVA, and blue (B) together or blue alone. The graph shown is representative of 3 independent experiments.

See also Figures S1 and S3.