title: The determination of sulfite levels and its oxidation in plant leaves.
abstract: Sulfur is the sixth most abundant element in life and an important building block of proteins and cellular metabolites. Plants like bacteria can synthesize their sulfur-containing biomolecules from sulfate, where sulfite is an intermediate of the sulfur assimilation pathway. Above a certain threshold SO(2)/sulfite is cytotoxic and is rapidly metabolized to avoid damage. However, the existing data show considerable differences in basal sulfite levels both between species and apparent discrepancies in measured levels in the same species. In order to resolve this question we employed a sulfite detection method using chicken sulfite oxidase and developed an independent enzymatic assay, based on the specific detection of sulfite by sulfite reductase and compared those measurements to a modified colorimetric fuchsin-based method, specific for sulfite detection. We show here that when properly used the sulfite levels detected by the three methods can yield identical results. Furthermore, to examine the capacity of the plant to detoxify sulfite we injected sub-lethal sulfite solutions (yet, several folds higher than the basal levels) into Arabidopsis and tomato leaves and monitored the excess sulfite turnover. Within 3h of sulfite injection, more than 80% of the injected sulfite in Arabidopsis and 91% in tomato were oxidized to sulfate, demonstrating the high capacity of the sulfite oxidation mechanism/s in plants.
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. bgalina@bgu.ac.il
authors.forename: Galina
authors.initials: G
authors.lastname: Brychkova
authors.forename: Dmitry
authors.initials: D
authors.lastname: Yarmolinsky
authors.forename: Robert
authors.initials: R
authors.lastname: Fluhr
authors.forename: Moshe
authors.initials: M
authors.lastname: Sagi
mesh_terms: D042931:Aldehyde Oxidase / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D018551:Solanum lycopersicum / Q000187:drug effects / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D010936:Plant Extracts / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D012015:Reference Standards; D013431:Sulfates / Q000378:metabolism; D050876:Sulfite Oxidase / Q000378:metabolism; D013447:Sulfites / Q000378:metabolism* / Q000633:toxicity; D014026:Nicotiana / Q000187:drug effects / Q000378:metabolism
chemical_list: D010936:Plant Extracts; D013431:Sulfates; D013447:Sulfites; D006861:Hydrogen Peroxide; D042931:Aldehyde Oxidase; D050876:Sulfite Oxidase; D005978:Glutathione; D003545:Cysteine