Figure 1. The carbonic anhydrases CA1 and CA4 are required for repression of stomatal development at elevated CO₂ concentrations.

a, Confocal images of the abaxial cotyledon epidermis of 10-day-old ca1 ca4 and WT (Col) seedlings grown at 500 p.p.m. CO₂. Scale bar, 100 µm. b, Stomatal index of WT and ca1 ca4 seedlings grown at 150 and 500 p.p.m. CO₂, showing an inverted stomatal development response to elevated CO₂ by the mutant. c, Elevated CO₂-induced changes in the stomatal index (data from b) shown as percentage changes in the stomatal index at 500 p.p.m.CO₂ relative to 150 p.p.m. CO₂. d, Stomatal density (data from c) for WT and ca1 ca4 seedlings. e, Stomatal index for six independent complementation lines of ca1 ca4 transformed with genomic copies of either A. thaliana CA1 (CA1-G) or A. thaliana CA4 (CA4-G). f, Elevated CO₂-induced changes in stomatal development (data from e). b–f, Statistical comparisons were made between CO₂ treatments (b and d) or were compared with the WT (c) or the ca1 ca4 data (f). Stomatal density and index measurements were conducted on 10-day-old seedlings. Error bars show mean ± s.e.m., n = 20 for b–f. ***, P<0.00005; **, P<0.005; *, P<0.05, using analysis of variance (ANOVA) and Tukey’s post-hoc test.