Antisense suppression of 2-cysteine peroxiredoxin in arabidopsis specifically enhances the activities and expression of enzymes associated with ascorbate metabolism but not glutathione metabolism

The aim of this study was to characterize the effect of decreased 2-cystein e peroxiredoxin (2-CP) on the leaf anti-oxidative system in Arabidopsis. At three stages of leaf development, two lines of transgenic Arabidopsis muta nts with decreased contents of chloroplast 2-CP were compared with wild ty- pe and a control line transformed with an empty vector. Glutathione content s and redox state were similar in all plants, and no changes in transcript levels for enzymes involved in glutathione metabolism were observed. Transc ript levels for chloroplastic glutathione peroxidase were much lower than t hose for 2-CP, and both cytosolic and chloroplastic glutathione peroxidase were not increased in the mutants. In contrast, the foliar ascorbate pool w as more oxidized in the mutants, although the difference decreased with pla nt age. The activities of thylakoid and stromal ascorbate peroxidase and pa rticularly monodehydroascorbate reductase were increased as were transcript s for these enzymes. No change in dehydroascorbate reductase activity was o bserved, and effects on transcript abundance for glutathione reductase, cat alase, and superoxide dismutase were slight or absent. The results demonstr ate that 2-CP forms an integral part of the anti-oxidant network of chlorop lasts and is functionally interconnected with other defense systems. Suppre ssion of 2-CP leads to increased expression of other anti-oxidative genes p ossibly mediated by increased oxidation state of the leaf ascorbate pool.