Figure 3.

cax1, cax3, and cax1/cax3 mutations impair IAA- but not NAA-inhibition of ABA-induced stomatal closure. A, IAA-inhibition of ABA-triggered stomatal closure is impaired in cax1, cax3, and cax1/cax3. Changes in stomatal aperture in response to 5 µM ABA were scored in the presence and absence of 10 µM IAA. Data are mean ± sem (n = 3 independent experiments, >90 stomata for each data point). B, IAA-inhibition of ABA-induced membrane depolarization is abolished in cax1/cax3 guard cells. Fluorescence ratio (ABA-treated/ABA + IAA-treated) in guard cells is shown for the purpose of clarity, because of the difference in steady-state membrane polarization between the wild type and cax1/cax3 (see Fig. 2C). Changes in guard cell-membrane polarization were assessed by DiBAC₄ fluorescence in response to ABA in the presence and absence of 10 µM IAA. Cells were challenged with 5 µM ABA at 8 min. Data are mean ± sem (793 cells, the wild type; 129 cells, the wild type + IAA; 917 cells, cax1/cax3; 187 cells, cax1/cax3 + IAA). C, 10 µM ACC inhibits ABA-induced stomatal closure in cax1, cax3, and cax1/cax3 as well as in the wild type. Data are mean ± sem (n = three independent experiments, >90 stomata for each data point). D, NAA inhibits ABA-triggered stomatal closure in cax1, cax3, and cax1/cax3 as well as in the wild type (5 µM ABA; 10 µM NAA). Data are mean ± sem (n = three independent experiments, >90 stomata for each data point). E, The AUX1 transporter inhibitor NOA blocks IAA inhibition of ABA-induced stomatal closure in the wild type. Stomatal apertures were measured from epidermal strips treated with 5 µM ABA and 5 µM IAA in the presence or absence of 10 µM NOA. Data are mean ± sem (n = four independent experiments, >82 stomata for each data point). Error bars are smaller than symbols when not visible.