Effects of sulfite and pH on abscisic acid-dependent transpiration and on stomatal opening

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Abstract
In rice, alday, wheat and tobacco (Nicotiana tabacum L. Samsun and Samsun NN) plants which contained large amounts of ABA, the transpiration rate decreased rapidly with 2 ppm SO2 fumigation and reached 20 to 65% of the initial level after 5- to 30-min exposure depending on their ABA contents. In the cases of broad bean and tobacco (N. glutinosa L.) with low ABA contents, the rate slightly increased for 20 and 40 min, respectively, after the start of the fumigation and then decreased gradually. The transpiration rates of corn and sorghum, in spite of their extremely low ABA contents, pronouncedly decreased with SO2 fumigation and reached 65 and 50%, respectively, of the initial levels after 40-min exposure. Foliar application of 0.04 N HC1 to N. tabacum L. Samsun NN leaves remarkably depressed the transpiration rate, while the application of 0.04 M Na2SO3 decreased the rate only to the same level as water treatment. Foliar application of either HCl or Na2SO3 to N. glutinosa L. leaves exerted little change in the transpiration rate. When 10−4M ABA was applied to broad bean leaves prior to HCl and Na2SO3 treatment, their transpiration rate was decreased by HCl, but not by Na2SO3 application. In sonicated epidermal strips peeled from broad bean leaves, Na2SO3 produced a slight increase in the stomatal aperture size in the absence of ABA, but showed no effect in the presence of ABA. The aperture size was identical in the pH range of 3.0 to 7.0 in the incubation medium. In the presence of ABA in the medium, the aperture size was small in the acidic region of pH with a minimal value at pH 4.0. ABA decreased the aperture size at concentrations above 10−9 M at pH 4.0 and 10−6 M at pH 7.0 in the medium. [2−14C] ABA uptake by epidermal strips was large in the acidic region, especially at pH 4.0.