title: Autophagy plays a role in chloroplast degradation during senescence in individually darkened leaves.
abstract: Chloroplasts contain approximately 80% of total leaf nitrogen and represent a major source of recycled nitrogen during leaf senescence. While bulk degradation of the cytosol and organelles in plants is mediated by autophagy, its role in chloroplast catabolism is largely unknown. We investigated the effects of autophagy disruption on the number and size of chloroplasts during senescence. When leaves were individually darkened, senescence was promoted similarly in both wild-type Arabidopsis (Arabidopsis thaliana) and in an autophagy-defective mutant, atg4a4b-1. The number and size of chloroplasts decreased in darkened leaves of wild type, while the number remained constant and the size decrease was suppressed in atg4a4b-1. When leaves of transgenic plants expressing stroma-targeted DsRed were individually darkened, a large accumulation of fluorescence in the vacuolar lumen was observed. Chloroplasts exhibiting chlorophyll fluorescence, as well as Rubisco-containing bodies, were also observed in the vacuole. No accumulation of stroma-targeted DsRed, chloroplasts, or Rubisco-containing bodies was observed in the vacuoles of the autophagy-defective mutant. We have succeeded in demonstrating chloroplast autophagy in living cells and provide direct evidence of chloroplast transportation into the vacuole.
authors.affiliation: Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Wada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ishida
authors.forename: Masanori
authors.initials: M
authors.lastname: Izumi
authors.forename: Kohki
authors.initials: K
authors.lastname: Yoshimoto
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ohsumi
authors.forename: Tadahiko
authors.initials: T
authors.lastname: Mae
authors.forename: Amane
authors.initials: A
authors.lastname: Makino
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D001343:Autophagy; D016922:Cellular Senescence / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism / Q000502:physiology; D002736:Chloroplasts / Q000235:genetics / Q000502:physiology*; D004269:DNA, Bacterial / Q000235:genetics; D016254:Mutagenesis, Insertional; D018515:Plant Leaves / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D010940:Plant Proteins; C036483:T-DNA; D002734:Chlorophyll; D012273:Ribulose-Bisphosphate Carboxylase