Figure 2.

The slac1 mutant of Arabidopsis slows stomatal opening and closing on light-dark transitions. Data are means ± se of n ≥ 12 independent experiments for wild-type (wt; open circles), slac1-1 (closed circles), and pSLAC1 (open triangles) plants. A, Transpiration rates recorded from intact Arabidopsis on transition from dark to 300 μmol m⁻² s⁻¹ light (left) and back to dark (right). Fitted half-times for opening (sigmoid) and closing (single exponential) are as follows: wild type, 22.4 ± 0.5 and 5.5 ± 0.2 min; slac1-1, 65.6 ± 0.4 and 50.7 ± 0.4 min; pSLAC1, 27.1 ± 0.4 and 6.3 ± 0.1 min. B, Stomatal apertures from epidermal peels. Data are normalized to initial and final apertures on transition to 300 μmol m⁻² s⁻¹ light. Opening half-times are as follows: wild type, 38 ± 5 min; slac1-1, 74 ± 8 min; pSLAC1, 34 ± 7 min. Apertures (initial/final, in μm) are as follows: wild type, 2.6 ± 0.2/4.2 ± 0.4; slac1-1, 4.0 ± 0.3/4.8 ± 0.4; pSLAC1, 2.6 ± 0.2/4.0 ± 0.4. C, Stomatal opening and closing recorded in leaves at 3-h intervals over 24 h. Note the slower response in the first three daylight hours for the mutant. slac1-1 apertures are significantly different (P < 0.001) at all times.