The effect of salicylic acid (SA) on stomatal aperture of 3～4 weeks' Vicia faba L. under different conditions was investigated. It was shown that stomatal closure responded to SA after 3 hours treatment. The concentration and pH of SA solution at different media affeeted SA to different extents. The degree of effects was concentration-dependent. With increasing SA concentration, the promotion effect on stomatal closure was enhanced. At 10 -3 mol L -1 SA exerted the most effect. The effect of SA was dependent on the pH of the solution. In the range of 10 -6 ～10 -3 mol L -1 as pH decreased, the effect of SA on stomatal closure was enhanced. SA 10 -4 mol L -1 in distilled water at pH 4 the percentage of inhibition on the stomatal aperture was 67%, while at pH 7 the percentage of inhibition was only 20%. The degrees of SA effect on stomatal aperture in distilled water、MES buffer solution and citric acid buffer solution were different. In MES buffer the effect of SA was lower than that in distilled water, or in citric acid buffer.
