title: The existence of phospholipase A(2) activity in plant mitochondria and its activation by hyperosmotic stress in durum wheat (Triticum durum Desf.).
abstract: The activity of mitochondrial phospholipase A(2) (PLA(2)) was shown for the first time in plants. It was observed in etiolated seedlings from durum wheat, barley, tomato, spelt and green seedlings of maize, but not in potato and topinambur tubers and lentil etiolated seedlings. This result was achieved by a novel spectrophotometric assay based on the coupled PLA(2)/lipoxygenase reactions using 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphatidylcholine as substrate; the mitochondrial localisation was assessed by checking recovery of marker enzymes. Durum wheat mitochondrial PLA(2) (DWM-PLA(2)) showed maximal activity at pH 9.0 and 1mM Ca(2+), hyperbolic kinetics (K(m)=90±6μM, V(max)=29±1nmolmin(-1)mg(-1) of protein) and inhibition by methyl arachidonyl fluorophosphonate, 5-(4-benzyloxyphenyl)-4S-(7-phenylheptanoylamino)pentanoic acid and palmityl trifluoromethyl ketone. Reactive oxygen species had no effect on DWM-PLA(2), that instead was activated by about 50% and 95%, respectively, under salt (0.21M NaCl) and osmotic (0.42M mannitol) stress imposed during germination. Contrarily, a secondary Ca(2+)-independent activity, having optimum at pH 7.0, was stress-insensitive. We propose that the activation of DWM-PLA(2) is responsible for the strong increase of free fatty acids recently measured in mitochondria under the same stress conditions [Laus, et al., J. Exp. Bot. 62 (2011) 141-154] that, in turn, activate potassium channel and uncoupling protein, able to counteract hyperosmotic stress.
authors.affiliation: Consiglio per la Ricerca e la sperimentazione in Agricoltura - Centro di Ricerca per la Cerealicoltura, Foggia, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Trono
authors.forename: Mario
authors.initials: M
authors.lastname: Soccio
authors.forename: Maura N
authors.initials: MN
authors.lastname: Laus
authors.forename: Donato
authors.initials: D
authors.lastname: Pastore
mesh_terms: D000222:Adaptation, Physiological; D015415:Biomarkers / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology* / Q000502:physiology; D008962:Models, Theoretical; D009995:Osmosis; D018384:Oxidative Stress; D064801:Phospholipase A2 Inhibitors; D054467:Phospholipases A2 / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012492:Salts; D036226:Seedlings / Q000201:enzymology / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology* / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D015415:Biomarkers; D004791:Enzyme Inhibitors; D064801:Phospholipase A2 Inhibitors; D010940:Plant Proteins; D015221:Potassium Channels; D017382:Reactive Oxygen Species; D012492:Salts; D014867:Water; D054467:Phospholipases A2