Effects of water stress on respiration in soybean leaves.
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.
Ribas-Carbo
Miquel
M
Grup de Recerca en Biologia de les Plantes en Condicions Mediterrànies, Universitat de les Illes Balears, Spain. mribas@uib.es
Taylor
Nicolas L
NL
Giles
Larry
L
Busquets
Silvia
S
Finnegan
Patrick M
PM
Day
David A
DA
Lambers
Hans
H
Medrano
Hipólito
H
Berry
Joseph A
JA
Flexas
Jaume
J
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
D000255:Adenosine Triphosphate; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D050994:Voltage-Dependent Anion Channels; D014867:Water; D000099188:Alternative Oxidase