Abstract
The effects of SO2 on stomatal aperture 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 aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO2.
A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO2 for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets.
There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO2. This correlation continued in leaves exposed to SO2 until visible, irreversible injury occurred, but then it disappeared.
The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO2 on stomatal behavior.
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