PLANT GLUTATHIONE PEROXIDASES

Oxidative stress in plants causes the induction of several enzymes, in cluding superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1 .11.1.11)and glutathione reductase (EC 1.6.4.2),. The first two are re sponsible for converting superoxide to H2O2 and its subsequent reducti on to H2O, and the third is involved in recycling of ascorbate. Glutat hione peroxidases (GPWs EC 1.11.1.9) are a family of key enzymes invol ved in scavenging oxyradicals in animals. Only recently. indications f or the existence of this enzyme in plants were reported. Genes with si gnificant sequence homology to one member of the animal GPX family, na mely phospholipid hydroperoxide glutathione peroxidase (PHGPX). were i solated from several plants. Cit-SAP, the protein product encoded by t he citrus csa gene, which is induced by salt-stress, is so far the onl y plant PHGPX that has been isolated and characterized. This protein d iffers from the animal PHGPX in its rate of enzymatic activity and in containing a Cys instead of selenocysteine (Sec) as its presumed catal ytic residue, The physiological role of Cit-SAP and Its homologs in ot her plants is not yet known.