Biochemical mechanisms of plant defense a central role for reactive oxygen species

In general mechanics stress is clearly defined as the point or degree of bending of an elastic system at the very point of just symptomless reversibility and irreversible deformation or break. In medicine and botany, stress is supposed to indicate all situations beyond normal, defined by the observer. All organs of higher plants (with some exceptions) perform aerobic metabolism and are thus subject to activated oxygen species. Oxygen oversaturation and thus oxygen stress may occur under various different conditions. Since most abiotic and biotic stress situations in plants result in the accelerated production of ROS oxidative stress is a common signaling event in plant stress and redox regulation therefore plays a central role in the stress signaling network (PASTORI & FOYER 2002). In this review basic reactions operating during stress and defence will be discussed where certain prooxidative situations and antioxidative processes in plants will be dealt with.