title: Effects of water stress on respiration in soybean leaves.
abstract: The effect of water stress on respiration and mitochondrial electron transport has been studied in soybean (Glycine max) leaves, using the oxygen-isotope-fractionation technique. Treatments with three levels of water stress were applied by irrigation to replace 100%, 50%, and 0% of daily water use by transpiration. The levels of water stress were characterized in terms of light-saturated stomatal conductance (g(s)): well irrigated (g(s) > 0.2 mol H(2)O m(-2) s(-1)), mildly water stressed (g(s) between 0.1 and 0.2 mol H(2)O m(-2) s(-1)), and severely water stressed (g(s) < 0.1 mol H(2)O m(-2) s(-1)). Although net photosynthesis decreased by 40% and 70% under mild and severe water stress, respectively, the total respiratory oxygen uptake (V(t)) was not significantly different at any water-stress level. However, severe water stress caused a significant shift of electrons from the cytochrome to the alternative pathway. The electron partitioning through the alternative pathway increased from 10% to 12% under well-watered or mild water-stress conditions to near 40% under severe water stress. Consequently, the calculated rate of mitochondrial ATP synthesis decreased by 32% under severe water stress. Unlike many other stresses, water stress did not affect the levels of mitochondrial alternative oxidase protein. This suggests a biochemical regulation (other than protein synthesis) that causes this mitochondrial electron shift.
authors.affiliation: Grup de Recerca en Biologia de les Plantes en Condicions Mediterrànies, Universitat de les Illes Balears, Spain. mribas@uib.es
authors.forename: Miquel
authors.initials: M
authors.lastname: Ribas-Carbo
authors.forename: Nicolas L
authors.initials: NL
authors.lastname: Taylor
authors.forename: Larry
authors.initials: L
authors.lastname: Giles
authors.forename: Silvia
authors.initials: S
authors.lastname: Busquets
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Finnegan
authors.forename: David A
authors.initials: DA
authors.lastname: Day
authors.forename: Hans
authors.initials: H
authors.lastname: Lambers
authors.forename: Hipólito
authors.initials: H
authors.lastname: Medrano
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Berry
authors.forename: Jaume
authors.initials: J
authors.lastname: Flexas
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis / Q000378:metabolism; D019069:Cell Respiration / Q000187:drug effects*; D004579:Electron Transport / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D024101:Mitochondrial Proteins; D010088:Oxidoreductases / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects* / Q000378:metabolism*; D010940:Plant Proteins; D018526:Plant Transpiration; D013025:Glycine max / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism; D014867:Water / Q000378:metabolism / Q000494:pharmacology*; D000099188:Alternative Oxidase
chemical_list: D000255:Adenosine Triphosphate; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D050994:Voltage-Dependent Anion Channels; D014867:Water; D000099188:Alternative Oxidase