ABSTRACT
The advantage of elevated Superoxide Dismutases (SOD) levels is obvious: more efficient scavenging of the superoxide radical would result in less superoxide-mediated damage. Superoxide radicals are mainly produced by the univalent reduction of O2 with electrons from the electron transport chains of chloroplasts, mitochondria, and cytosol and consequently, most of the SOD activity is localized in these compartments. In plants, the herbicide paraquat is often used as a model system to study the effects of superoxide-mediated damage in the chloroplasts. The sulfur trioxide radical is more important for the propagation of radical production than the superoxide radical, which could explain why SO2 damage takes place even at relatively low light intensities. Elevated SOD levels may impair an adequate defense response against oxidative stress, as superoxide may function as a second messenger triggering the induction of certain defense mechanisms.
