Figure 7.

Light-induced stomatal aperture was reduced in chx20 mutants. Aperture size is expressed as a ratio of maximal aperture size per length of guard cell (GC) pair. Twenty apertures were measured per treatment. Bar indicates se. A, Three alleles show reduced stomatal opening. Excised leaves of dark-adapted wild type (WT1-2) and three mutants (chx20) were given 150 μE m⁻² s⁻¹ light or dark for 3 h. Leaves were placed in a solution containing 5 mm KCl and 10 mm MES-KOH at pH 6.15. Average light-enhanced pore size is shown from five independent experiments. B, Reduction in aperture size is independent of K⁺ levels. Isolated epidermis from wild type and chx20-3 were incubated separately in 10 mm MES-Tris at pH 6.15 without K⁺ at dark for 3 h. KCl was then added to 0.1, 1, or 10 mm, and the epidermal strips were irradiated for 3 h as in A. Results of dark (gray) and light (white) treatment are from one representative experiment of three. C, Effect of pH on stomatal opening. Isolated epidermis from wild type and chx20-3 were separately incubated 3 h in the dark in 5 mm KCl buffered to pH 6.15, 7.0, 7.5, or 8.0. Epidermal strips were exposed to light for 3 h. Average ratio of light-stimulated aperture/GC length of three independent experiments is shown.