Fig. 1.

Hypersensitive ABA responses of fer mutant plants. (A–C) ABA sensitivity in seedlings. Approximately 150 seeds from four independent seed lots of simultaneously grown WT (Columbia-0 and C24), fer-4, fer-5, and srn mutants were sown on agar plates supplemented with ABA (mixed isomers; Sigma-Aldrich A1049). (A) The images of plants were taken on day 9 after germination on MS agar medium supplemented with 0 μM (a) or 0.25 μM ABA (b). (B) Close-up images show Col-0 WT (Top), fer-4 (Middle), and fer-5 (Bottom) seedlings taken from Ab. (C) Images indicate srn mutant and WT C24 plants on day 8 after germination on MS agar medium supplemented with 0 μM (MS) or 0.5 μM ABA (MS+ABA). (D) ABA-induced growth inhibition in roots. Five-day-old seedlings grown on the MS medium were transferred to MS medium containing 3 μM ABA. Root length was measured 4 d after transfer. Each data point is the average ± SE of three independent experiments with 10 plants each. (E) Stomatal aperture before and after ABA treatment of fer-4 and WT leaves. Data are presented as average ± SE of three replicates with 10 apertures each. Three independent experiments yielded similar results. (F) Quantification of ROS production in guard cells of the WT and fer-4 plants after ABA treatment. Confocal fluorescence intensities were quantified as average pixel intensities in three random regions of each guard cell by using the OLYMPUS FV1000 software. The relative ROS production of each treatment was normalized to untreated WT (100%). Data are average values ± SE of nine guard cells per genotype in one experiment. Four independent experiments were conducted with similar results.