title: Salt stress-induced cell death in the unicellular green alga Micrasterias denticulata.
abstract: Programmed cell death (PCD) is a key element in normal plant growth and development which may also be induced by various abiotic and biotic stress factors including salt stress. In the present study, morphological, biochemical, and physiological responses of the theoretically immortal unicellular freshwater green alga Micrasterias denticulata were examined after salt (200 mM NaCl or 200 mM KCl) and osmotic stress induced by iso-osmotic sorbitol. KCl caused morphological changes such as cytoplasmic vacuolization, extreme deformation of mitochondria, and ultrastructural changes of Golgi and ER. However, prolonged salt stress (24 h) led to the degradation of organelles by autophagy, a special form of PCD, both in NaCl- and KCl-treated cells. This was indicated by the enclosure of organelles by ER-derived double membranes. DNA of NaCl- and KCl-stressed cells but not of sorbitol-treated cells showed a ladder-like pattern on agarose gel, which means that the ionic rather than the osmotic component of salt stress leads to the activation of the responsible endonuclease. DNA laddering during salt stress could be abrogated by addition of Zn(2+). Neither cytochrome c release from mitochondria nor increase in caspase-3-like activity occurred after salt stress. Reactive oxygen species could be detected within 5 min after the onset of salt and osmotic stress. Respiration, photosynthetic activity, and pigment composition indicated an active metabolism which supports programmed rather than necrotic cell death in Micrasterias after salt stress.
authors.affiliation: Plant Physiology Division, Cell Biology Department, University of Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria.
authors.forename: Matthias Josef
authors.initials: MJ
authors.lastname: Affenzeller
authors.forename: Anza
authors.initials: A
authors.lastname: Darehshouri
authors.forename: Ancuela
authors.initials: A
authors.lastname: Andosch
authors.forename: Cornelius
authors.initials: C
authors.lastname: Lütz
authors.forename: Ursula
authors.initials: U
authors.lastname: Lütz-Meindl
mesh_terms: D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D000460:Chlorophyta / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D045304:Cytochromes c / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D009997:Osmotic Pressure / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010788:Photosynthesis / Q000187:drug effects; D010860:Pigments, Biological / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects*; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology
chemical_list: D010860:Pigments, Biological; D017382:Reactive Oxygen Species; D012965:Sodium Chloride; D045304:Cytochromes c; D053148:Caspase 3; D015032:Zinc