Die Sulfitolyse von Thioredoxinen Eine Schlüsselreaktion für die Phytotoxizität von Schwefeldioxid in Pflanzen

Ample evidence exists that the phytotoxic action of sulfur dioxide in plants is initiated and propagated by impairment of their thioredoxin systems, which by their redox status control the light-dark regulation and productivity of chloroplast metabolism. We have shown that oxidized thioredoxin reacts readily with sulfite ions under sulfitolysis of its exposed disulfide bond and formation of an inactive S-sulfonyl thioredoxin. Accumulation of such modified proteins is suggested to mark the specific threshold concentration of SO₂ toxicity in a plant. The adverse effects are potentiated intracellularly by an induction of excess H₂O₂ synthesis which will oxidize additional SH groups and make them susceptible to further sulfitolysis and incapacitation.     

Haloacetic acids,phytotoxic secondary air pollutants

Haloacetic acids are atmospheric oxidation products of airborne C₂-halocarbons which are important solvents and propellants. Levels of trichloroacetate (TCA) in conifer needles from mountain ranges in Germany (Black Forest, Erzgebirge) and from two sites in Finland are compared; TCA is present in conifer needles at concentrations up to 0.7 μmol/kg, MCA up to 0.2 μmol/kg. At the Finnish sites, TCA-concentrations and branch degeneration symptoms of Scots pine are correlated. Monochloroacetate (MCA) has been determined in needle samples from Southern Germany in concentrations exceeding its phytotoxicity threshold towards photoautotrophic organisms. Data on atmospheric chloroacetate levels in Germany are also given; ambient air levels of chloroacetic acids range from about 2 pmol/m³ (TCA) to 390 pmol/m³ (MCA). TCA and dichloroacetic acid (DCA) arise from atmospheric oxidation of airborne C₂-chlorocarbons, while the source of MCA is not yet known; several tentative pathways are suggested.