Mutual Antagonism of Sulfur Dioxide and Abscisic Acid in Their Effect on Stomatal Aperture in Broad Bean (Vicia faba L.) Epidermal Strips

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Abstract
Abscisic acid (ABA) was found to counteract the stomatal opening in Vicia faba L. caused by SO2. The antagonism between SO2 and ABA was mutual, and their combined effect depended upon which compound was in the greatest concentration. Stomatal apertures were monitored in detached epidermal strips floated in the light on aqueous solutions of SO2 (sulfurous acid) and/or ABA in 0.01 molar sodium citrate buffer (pH 5.8). Low concentrations of sulfurous acid (10−10 to 10−7 molar) increased stomatal aperture, but concentrations greater than 10−5 molar decreased it. A progressive decrease in aperture size occurred as ABA was increased from 10−10 to 10−5 molar.