Effects of sulphur dioxide and ozone, singly or in combination, on membrane permeability

Abstract

The effects of 0.15 ppm SO2 and (or) 0.15 ppm O3 on membrane permeability, measured by electrical conductivity of solute leakage, were determined for soybean, white bean, cucumber and radish. Solute leakage increased significantly prior to visible injury for soybean and white bean exposed to 0.15 ppm O3 alone. This results in water-soaked lesions on the upper leaf surface prior to visible colored necrotic lesions and is representative of a leaky plasmalemma. The SO2-O3 mixture did not increase solute leakage above that of the control for white bean and soybean. The presence of SO2 in combination with O3 attenuates or reduces the effects of O3 on increasing membrane permeability of white bean and soybean. O3 alone did not affect membrane permeability in cucumber and radish. The SO2-O3 mixture, which produced more injury than O3 alone, increased membrane permeability temporarily for radish and cucumber, but this occurred only after visible injury symptoms appeared. Overall, the effects of the pollutants singly or in combination on membrane permeability apparently explain differences in species responses.