Effect of Abscisic Acid on the Transpiration of Zea mays

Intact plants of Zea mays L. were treated with foliar sprays of cis-trans-abscisic acid (ABA) at concentrations from 10^?9 to 10^?4M. Even the lowest concentration caused a reduction of the transpiration rate as measured between 1 and 33 h after spraying. With increasing ABA concentrations, there was a nearly linear relationship between the logarithm of the ABA concentration and the (decreasing) transpiration rate within that period. Subsequently a partial recovery of the transpiration rate set in, beginning progressively later as the ABA concentration was increased. After 5 1/2 days the transpiration rate of plants treated with 10^?9 and 10^?8M was nearly back to normal, whereas plants treated with 10^?4M transpiration at only about 2/3 their normal rate. In experiments with detached maize leaves supplied with water or ABA solutions (10^?8 to 10^?5M) through their cut bases, the transpiration of control leaves decreased gradually to a low level in 24 h. ABA caused a marked and rapid reduction of the transpiration rate compared to that of the controls. After a few hours, the transpiration of the treated leaves decreased at a slower rate than that of the controls, thus approaching the control values. After 35 h, the transpiration of leaves treated with 10^?5M ABA was nearly the same as in untreated leaves. Exchanging the ABA solution for distilled water after 24 h had little effect on the subsequent course of the transpiration rate.