Some Effects of Abscisic Acid and Water Stress on Stomata ofVicia fabaL.

Vicia faba seedlings grown under a plastic tent in the laboratory were either watered well throughout their growth period or were subjected to a water stress treatment for several days prior to an experimental treatment. The effects of a further water stress treatment or an application of an aqueous solution of abscisic acid (ABA) on the stomata of these plants were determined. Stomata of previously water-stressed plants proved to be more sensitive than stomata of well watered plants to ABA applied through the petiole via the transpiration stream and sprayed onto leaf surfaces. Stomata of previously water-stressed plants closed more rapidly and to a greater degree than stomata of well watered plants. The hormone had only a small effect when applied directly to epidermal fragments removed from both groups of plants. Stomata of plants which had received a water stress pretreatment were less sensitive to a subsequent period of water stress than were stomata of previously well watered plants. It is proposed that stomatal adaptation to water stress may be related to changes in the hormonal balance of the plant.