PLANT PHYSIOLOGY , Vol 107, Issue 4 1187-1194, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Drought Stress, Permeability to O2 Diffusion, and the Respiratory Kinetics of Soybean Root Nodules
L. D. del Castillo and D. B. Layzell
Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
In legume nodules, treatments such as detopping or nitrate fertilization
inhibit nodule metabolism and N2 fixation by decreasing the nodule's
permeability to O2 diffusion, thereby decreasing the infected cell O2
concentration (Oi) and increasing the degree to which nodule metabolism is
limited by O2 availability. In the present study we used nodule oximetry to
assess and compare the role of O2 limitation in soybean (Glycine max L.
Merr) nodules inhibited by either drought or detopping. Compared to
detopping, drought caused only minor decreases in Oi, and when the external
O2 concentration was increased to raise Oi, the infected cell respiration
rate in the drought-stressed plants was not stimulated as much as it was in
the nodules of the detopped plants. Unlike those in detopped plants,
nodules exposed to moderate drought stress displayed an O2-sufficient
respiration rate that was significantly lower than that in control nodules.
Despite possible side effects of oximetry in altering nodule metabolism,
these results provided direct evidence that, compared to detopping, O2
limitation plays a minor role in the inhibition of nodule metabolism during
drought stress and changes in nodule permeability are the effect, not the
cause, of a drought-induced inhibition of nodule metabolism and the
O2-suffiecient rate of respiration.
