The effects of air pollutants on stomatal aperture and epidermal cells of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal opening and the stomatal conductance, measured with a porometer, was examined at different leaf ages.
The stomatal closure was observed during the exposure of SO₂+NO₂+O₃ in low concentrations (0.1 to 0.2μl·l^-1). There was a tendency for the extent of closure to increase in rise of concentration and mixture of these pollutants. The stomatal response to high concentration O₃(1.0μl·l^-1) fluctuated in the region at a distance from veinlet because of stomatal opening induced by water-soaking. The transient opening was less common in stomata near veins and veinlets.
There was a good correlation between actual stomatal opening and stomatal conductance in the same area of the leaf. However, the regression curves varied with the leaf age.
The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants on stomatal behavior.