The role of superoxide dismutase in the susceptibility of bean leaves to ozone injury

Abstract

The primary leaves of bush bean plants pretreated daily with very low levels of ozone (0.02 or 0.05 ppm) pass through stages of varying susceptibility to a subsequent acute dose. This variation in response can only partly be accounted for by stomatal behaviour. Present studies indicate that the levels of the oxyradical scavenger, superoxide dismutase (SOD), assayed in leaf homogenates, appear to play no role in the phenomenon. No observed changes in the levels of extracted SOD following various low ozone pretreatment regimes could be related to changes in susceptibility to acute injury, in comparisons with control plants maintained in charcoal-filtered air prior to acute fumigation. The only significant increases in SOD levels which appeared to be directly related to ozone exposure occurred simultaneously with the appearance of visible symptoms of injury from either the cumulative chronic or acute ozone exposures.