Peroxisomes as a source of reactive oxygen species and nitric oxide signalmolecules in plant cells

The important role of plant peroxisomes in a variety of metabolic reactions such as photorespiration, fatty acid beta -oxidation, the glyoxylate cycle and generation-degradation of hydrogen peroxide is well known. In recent y ears, the presence of a novel group of enzymes, mainly involved in the meta bolism of oxygen free-radicals, has been shown in peroxisomes. In addition to hydrogen peroxide, peroxisomes can generate superoxide-radicals and nitr ic oxide, which are known cellular messengers with a variety of physiologic al roles in intra- and inter-cellular communication. Nitric oxide and hydro gen peroxide can permeate the peroxisomal membrane and superoxide radicals can be produced on the cytosolic side of the membrane. The signal molecule- generating capacity of peroxisomes can have important implications for cell ular metabolism in plants, particularly under biotic and abiotic stress.