Kinetics of leaf oxygen uptake represent in planta activities of respiratory electron transport and terminal oxidases.
We present, for the first time, the oxygen response kinetics of mitochondrial respiration measured in intact leaves (sunflower and aspen). Low O(2) concentrations in N(2) (9-1500 ppm) were preset in a flow-through gas exchange measurement system, and the decrease in O(2) concentration and the increase in CO(2) concentration as result of leaf respiration were measured by a zirconium cell O(2) analyser and infrared-absorption CO(2) analyser, respectively. The low O(2) concentrations little influenced the rate of CO(2) evolution during the 60-s exposure. The initial slope of the O(2) uptake curve on the dissolved O(2) concentration basis was relatively constant in leaves of a single species, 1.5 mm s(-1) in sunflower and 1.8 mm s(-1) in aspen. The apparent K(0.5)(O(2)) values ranged from 0.33 to 0.67 microM in sunflower and from 0.33 to 1.1 microM in aspen, mainly because of the variation of the maximum rate, V(max) (leaf temperature 22 degrees C). The initial slope of the O(2) response of respiration characterizes the catalytic efficiency of terminal oxidases, an important parameter of the respiratory machinery in leaves. The plateau of the response characterizes the activity of the mitochondrial electron transport chain and is subject to regulations in accordance with the necessity for ATP production. The relatively low oxygen conductivity of terminal oxidases means that in leaves, less than 10% of the photosynthetic oxygen can be reassimilated by mitochondria.
Laisk
Agu
A
Institute for Molecular and Cell Biology, Tartu University, Riia street 23, Tartu 51010, Estonia. alaisk@ut.ee
Oja
Vello
V
Eichelmann
Hillar
H
D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D004579:Electron Transport; D007700:Kinetics; D010088:Oxidoreductases / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism*; D032107:Populus / Q000201:enzymology / Q000378:metabolism / Q000502:physiology
D010940:Plant Proteins; D002245:Carbon Dioxide; D010088:Oxidoreductases; D010100:Oxygen