Studies on Molecular Basis for Reactive Nitrogen Metabolism in Plants

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(1)Arabidopsis 2-Cys Peroxiredoxin as Metabolic Enzyme for Reactive Nitrogen SpeciesPurified recombinant proteins of a thiol-dependent peroxidase called 2-Cys peroxiredoxin (2CPRX) from Arabidopsis were shown to metabolically scavenge peroxynitrite, a reactive nitrogen species (RNS) known as a potent oxidizing and nitrating agent. The Arabidopsis 2CPRX cDNA was functionally able to complement the hypersensitivity of a yeast mutant to nitrite-derived RNS. These results demonstrated a new role of plant 2CPRX as a critical determinant of the resistance to RNS, and support the existence of a plant enzymatic basis for RNS metabolism.(2)Functional relevance of Arabidopsis Non-Symbiotic Hemoglobin to Reactive Nitrogen SpeciesPlants ubiquitously contain non-symbiotic hemoglobins whose physiological role remains obscure. Purified recombinant proteins of an Arabidopsis non-symbiotic hemoglobin (AtGLB1) were shown to possess peroxidase-like activity that can oxidize nitrite as electron donor to f … More orm nitrogen dioxide radicals. AtGLB1 mRNA significantly accumulated in Arabidopsis seedlings that had been exposed to nitrite. These results support the physiological relevance of the function of AtGLB1 to nitrite and nitrite-derived RNS, and suggest a new possible route for RNS production in plants, apart from nitric-oxide (NO) biogenesis.(3)Plant-Physiological Impact of Molecular-Genetic Alteration in S-Nitrosothiol MetabolismS-Nitrosothiols (RSNO), a major form of RNS, are NO-adducts of thiol compounds such as S-nitrosoglutathione (GSNO) that is a representative RSNO with biological relevance. Overexpression of Arabidopsis GSNO reductase (GSNOR), the only known plant enzyme possibly involved in RSNO metabolism, led to a significant RSNO reduction in transgenic Arabidopsis. In contrast, knocking out the GSNOR gene resulted in RSNO over-accumulation. Metabolic studies of NO_2 assimilation in transgenic Arabidopsis overexpressing GSNOR suggested the existence of a crosstalk between RNS metabolism and the primary nitrogen assimilation. These results strongly indicate GSNOR as a key enzyme in RSNO metabolism and its potential importance in plant nitrogen metabolism. Less