Fig. 4.

CO₂ does not rapidly elevate ABA concentration in guard cells. (A and B) Time-resolved ABAleon2.15 emission ratios in guard cells in response to CO₂ changes and ABA application. Intact leaf epidermes were perfused with buffer containing 115 ppm CO₂ or 535 ppm CO₂ (21) and then switched to a 10 μM ABA containing buffer as indicated. Data in A and B are averages of normalized emission ratios each from six guard cells. Error bars represent SEM. (C) Representative images of pRAB18::GFP promoter reporter expression in guard cells in intact leaves in response to ABA or EtOH as control treatment. Rosette leaves of 4-wk-old plants were sprayed with 10 μM ABA or 0.01% EtOH solutions and observed after 24 h. (D) Average pRAB18::GFP promoter reporter. emission intensity in guard cells under the imposed treatments in C. (E) Representative images of pRAB18::GFP promoter reporter expression in guard cells in intact leaves in response to the indicated CO₂ concentration treatments. Four-week-old plants were grown in a growth chamber at 150 ppm CO₂ for 2 d and then either shifted to 900 ppm CO₂ or maintained at 150 ppm CO₂ for 24 and 48 h. (F) Average pRAB18::GFP promoter reporter emission intensities in guard cells under the imposed treatments in E. GFP intensities were calculated by averaging at least 50 pairs of guard cells in the fourth-youngest leaf of each plant. (Scale bar, 50 μm.) Data represent mean ± SEM. n = 6 plants for each treatment. **P < 0.01 by Student t test.