Radical Production and Scavenging in the Chloroplasts

Abstract

Under the conditions where leaves are exposed to high photon flux densities in excess of their photon-utilizing capacity,excess photons produce active oxygens, radicals and triplet excited pigments, which cause photoinhibition of photosynthesisas a result of oxidation of target molecules. After a brief discussion on the relationship between radicals and active oxygens,the primary target molecules of these reactive molecules are discussed in relation to photoinhibition. Subsequently, the photoproductionof active oxygens and radicals in chloroplasts is described. To avoid photoinhibition, prompt scavenging of active oxygensand radicals at the sites where they are produced is essential in the chloroplasts. The enzymes participating in this scavengingand their microcompartmentation in chloroplasts are reviewed.