title: The different fates of mitochondria and chloroplasts during dark-induced senescence in Arabidopsis leaves.
abstract: Senescence is an active process allowing the reallocation of valuable nutrients from the senescing organ towards storage and/or growing tissues. Using Arabidopsis thaliana leaves from both whole darkened plants (DPs) and individually darkened leaves (IDLs), we investigated the fate of mitochondria and chloroplasts during dark-induced leaf senescence. Combining in vivo visualization of fates of the two organelles by three-dimensional reconstructions of abaxial parts of leaves with functional measurements of photosynthesis and respiration, we showed that the two experimental systems displayed major differences during 6 d of dark treatment. In whole DPs, organelles were largely retained in both epidermal and mesophyll cells. However, while the photosynthetic capacity was maintained, the capacity of mitochondrial respiration decreased. In contrast, IDLs showed a rapid decline in photosynthetic capacity while maintaining a high capacity for mitochondrial respiration throughout the treatment. In addition, we noticed an unequal degradation of organelles in the different cell types of the senescing leaf. From these data, we suggest that metabolism in leaves of the whole DPs enters a 'stand-by mode' to preserve the photosynthetic machinery for as long as possible. However, in IDLs, mitochondria actively provide energy and carbon skeletons for the degradation of cell constituents, facilitating the retrieval of nutrients. Finally, the heterogeneity of the degradation processes involved during senescence is discussed with regard to the fate of mitochondria and chloroplasts in the different cell types.
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE-901 87 Umeå, Sweden.
authors.forename: Olivier
authors.initials: O
authors.lastname: Keech
authors.forename: Edouard
authors.initials: E
authors.lastname: Pesquet
authors.forename: Abdul
authors.initials: A
authors.lastname: Ahad
authors.forename: Anna
authors.initials: A
authors.lastname: Askne
authors.forename: Dag
authors.initials: D
authors.lastname: Nordvall
authors.forename: Sharvani Munender
authors.initials: SM
authors.lastname: Vodnala
authors.forename: Hannele
authors.initials: H
authors.lastname: Tuominen
authors.forename: Vaughan
authors.initials: V
authors.lastname: Hurry
authors.forename: Pierre
authors.initials: P
authors.lastname: Dizengremel
authors.forename: Per
authors.initials: P
authors.lastname: Gardeström
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D002736:Chloroplasts / Q000502:physiology*; D003624:Darkness; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate