Activated oxygen and free oxygen radicals in pathology: New insights and analogies between animals and plants

All organisms are subject to diseases and forced to adapt to unfavourable c onditions. In this context, plants, animals and lower organisms are equally concerned. Both diseases and environmental adaptations are frequently conn ected with altered oxygen metabolism chemically characterized as a transiti on from heterolytic (two electron abstraction or donation) to increased hom olytic (one electron transition) processes. Homolytic reactions generate ra dicals which may react in an aggressive manner, thus damaging cellular comp artments, tissues and finally organisms and populations. Therefore, these r eactions generating reactive oxygen species (ROS) are generally counterbala nced by an endogenous increase of antioxidative processes or externally by supportive medication. In the last twenty years, several unexpected similar ities in plants and animals concerning oxygen activation and radical-driven processes have been fc,found. In this review, homologous or corresponding processes and activities in plants and animals are compared. (C) Elsevier, Paris.