title: Sulfite reductase protects plants against sulfite toxicity.
abstract: Plant sulfite reductase (SiR; Enzyme Commission 1.8.7.1) catalyzes the reduction of sulfite to sulfide in the reductive sulfate assimilation pathway. Comparison of SiR expression in tomato (Solanum lycopersicum 'Rheinlands Ruhm') and Arabidopsis (Arabidopsis thaliana) plants revealed that SiR is expressed in a different tissue-dependent manner that likely reflects dissimilarity in sulfur metabolism between the plant species. Using Arabidopsis and tomato SiR mutants with modified SiR expression, we show here that resistance to ectopically applied sulfur dioxide/sulfite is a function of SiR expression levels and that plants with reduced SiR expression exhibit higher sensitivity than the wild type, as manifested in pronounced leaf necrosis and chlorophyll bleaching. The sulfite-sensitive mutants accumulate applied sulfite and show a decline in glutathione levels. In contrast, mutants that overexpress SiR are more tolerant to sulfite toxicity, exhibiting little or no damage. Resistance to high sulfite application is manifested by fast sulfite disappearance and an increase in glutathione levels. The notion that SiR plays a role in the protection of plants against sulfite is supported by the rapid up-regulation of SiR transcript and activity within 30 min of sulfite injection into Arabidopsis and tomato leaves. Peroxisomal sulfite oxidase transcripts and activity levels are likewise promoted by sulfite application as compared with water injection controls. These results indicate that, in addition to participating in the sulfate assimilation reductive pathway, SiR also plays a role in protecting leaves against the toxicity of sulfite accumulation.
authors.affiliation: Jacob Blaustein Institute for Desert Research, Albert Katz Department of Dryland Biotechnologies, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Yarmolinsky
authors.forename: Galina
authors.initials: G
authors.lastname: Brychkova
authors.forename: Robert
authors.initials: R
authors.lastname: Fluhr
authors.forename: Moshe
authors.initials: M
authors.lastname: Sagi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D055162:Biocatalysis / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D015151:Immunoblotting; D018551:Solanum lycopersicum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D010944:Plants / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013440:Sulfides / Q000378:metabolism; D013447:Sulfites / Q000378:metabolism* / Q000633:toxicity; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D013440:Sulfides; D013447:Sulfites; D050862:Oxidoreductases Acting on Sulfur Group Donors; C488954:SIR protein, Arabidopsis