title: An essential role for tomato sulfite oxidase and enzymes of the sulfite network in maintaining leaf sulfite homeostasis.
abstract: Little is known about the homeostasis of sulfite levels, a cytotoxic by-product of plant sulfur turnover. By employing extended dark to induce catabolic pathways, we followed key elements of the sulfite network enzymes that include adenosine-5'-phosphosulfate reductase and the sulfite scavengers sulfite oxidase (SO), sulfite reductase, UDP-sulfoquinovose synthase, and β-mercaptopyruvate sulfurtransferases. During extended dark, SO was enhanced in tomato (Solanum lycopersicum) wild-type leaves, while the other sulfite network components were down-regulated. SO RNA interference plants lacking SO activity accumulated sulfite, resulting in leaf damage and mortality. Exogenous sulfite application induced up-regulation of the sulfite scavenger activities in dark-stressed or unstressed wild-type plants, while expression of the sulfite producer, adenosine-5'-phosphosulfate reductase, was down-regulated. Unstressed or dark-stressed wild-type plants were resistant to sulfite applications, but SO RNA interference plants showed sensitivity and overaccumulation of sulfite. Hence, under extended dark stress, SO activity is necessary to cope with rising endogenous sulfite levels. However, under nonstressed conditions, the sulfite network can control sulfite levels in the absence of SO activity. The novel evidence provided by the synchronous dark-induced turnover of sulfur-containing compounds, augmented by exogenous sulfite applications, underlines the role of SO and other sulfite network components in maintaining sulfite homeostasis, where sulfite appears to act as an orchestrating signal molecule.
authors.affiliation: Plant Stress Laboratory, French Associates Institute for Agriculture and Biotechnology of Drylands, Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
authors.forename: Galina
authors.initials: G
authors.lastname: Brychkova
authors.forename: Vladislav
authors.initials: V
authors.lastname: Grishkevich
authors.forename: Robert
authors.initials: R
authors.lastname: Fluhr
authors.forename: Moshe
authors.initials: M
authors.lastname: Sagi
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology / Q000235:genetics; D003624:Darkness; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006706:Homeostasis; D015151:Immunoblotting; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics; D018515:Plant Leaves / Q000201:enzymology* / Q000235:genetics; D034622:RNA Interference; D013312:Stress, Physiological; D050876:Sulfite Oxidase / Q000235:genetics / Q000378:metabolism*; D013447:Sulfites / Q000378:metabolism*
chemical_list: D013447:Sulfites; D002734:Chlorophyll; D050862:Oxidoreductases Acting on Sulfur Group Donors; D050876:Sulfite Oxidase; C019618:adenylylsulfate reductase