Figure 4.

Apoplastic pH is altered in cax1, cax3, and cax1/cax3. A, Lower extracellular pH (5.6) restores IAA-inhibition of ABA-induced stomatal closure in cax1, cax3, and cax1/cax3. Data are mean ± sem (n = 3 independent experiments, >86 stomata for each data point). B, Measurements of apoplastic pH reveal that cax1, cax3, and cax1/cax3 plants have a higher pH compared with the wild type. Emission wavelength of HPTS was collected at both 510 and 530 nm. Error bars in the graph represent sem of at least two independent experiments. At least 50 leaves were used for each experiment. C, Western-blot analysis of plasma membrane proteins shows that the P-type AHA protein level is significantly reduced in cax1, cax3, and cax1/cax3 compared with the wild type. Quantification of AHA protein level was normalized to the average protein amount from silver-stained gels. Error bars in the graph represent sem, n = three independent experiments.