title: Compartment-specific investigations of antioxidants and hydrogen peroxide in leaves ofArabidopsis thalianaduring dark-induced senescence.
abstract: The aim of this study was to gain insight into the compartment-specific roles of ascorbate and glutathione in leaf senescence inArabidopsis thaliana. The subcellular distribution of ascorbate, glutathione, and hydrogen peroxide (H2O2) was analyzed by transmission electron microscopy and correlated with the activity of antioxidative enzymes in wildtype plants and the ascorbate- and glutathione-deficient mutantsvtc2-1andpad2-1, respectively. Both mutants showed earlier and stronger senescence than the wildtype indicating the importance of a functioning ascorbate and glutathione cycle in the induction and regulation of senescence. Glutathione levels dropped drastically and up to 93 % in all cell compartments of wildtype plants and thevtc2-1mutant within the first day of dark-induced senescence while ascorbate contents remained unchanged until the very end. Glutathione contents in mitochondria ofpad2-1mutants decreased more slowly over the first 7 days than compared to the other plants indicating an important role of glutathione in mitochondria in this mutant during senescence. The strongest decrease (84 %) of glutathione contents in wildtype plants at this time point was found in mitochondria indicating an important role of mitochondria for the induction of senescence and cell death events. Due to the general decrease of the antioxidative capacity, a strong accumulation of H2O2was observed in cell walls, plastids, and the cytosol in all plants. Activities of glutathione reductase, dehydroascorbate reductase and catalase were strongly reduced while ascorbate peroxidase and monodehydroascorbate reductase were increased. The initial rapid drop of glutathione levels seemed to be the trigger for senescence, while ascorbate appeared to be the key factor in regulating senescence through controlling H2O2levels by the oxidation of reduced ascorbate to monodehydroascorbate and the subsequent reduction to ascorbate by monodehydroascorbate reductase.
authors.affiliation: University of Teacher Education Styria, Hasnerplatz 12, 8010 Graz, Austria.
authors.forename: Nora
authors.initials: N
authors.lastname: Luschin-Ebengreuth
authors.affiliation: Center for Microscopy and Imaging, Baylor University, One Bear Place #97046, Waco, TX 76798 USA.
authors.forename: Bernd
authors.initials: B
authors.lastname: Zechmann
keywords: Arabidopsis; Ascorbate; Glutathione; Hydrogen peroxide; Senescence; Transmission electron microscopy