PLANT PHYSIOLOGY , Vol 108, Issue 1 235-240, Copyright © 1995 by American Society of Plant Biologists
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PLANT-MICROBE AND PLANT-INSECT INTERACTIONS |
Oxygen-Induced Membrane Depolarizations in Legume Root Nodules (Possible Evidence for an Osmoelectrical Mechanism Controlling Nodule Gas Permeability)
R. F. Denison and T. B. Kinraide
Appalachian Soil and Water Conservation Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Beckley, West Virginia 25802
Various stresses trigger rapid and reversible decreases in the O2
permeability (PO) of legume root nodules. Several possible mechanisms have
been proposed, but no supporting data have previously been presented that
meet the requirements for both rapidity and reversibility. Stomatal
regulation of gas permeability in leaves involves electrically driven
fluxes of inorganic osmoticants, so we investigated the possibility of a
somewhat similar mechanism in nodules. We used microelectrodes to monitor
membrane potential in intact, attached nodules of Glycine max, Medicago
sativa, Lotus corniculatus, and Trifolium repens while controlling external
O2 concentration and, in the case of G. max, measuring PO with a nodule
oximeter. A 1- to 2-min exposure to 100 kPa O2 was found to induce rapid
and reversible membrane depolarizations in nodules of each species. This
depolarization (which, to our knowledge, is unique to nodules) is
accompanied by reversible decreases in PO in G. max nodules. An
osmoelectrical mechanism for control of nodule gas permeability, consistent
with these data, is presented.