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Plant Physiology 58:304-308 (1976)
© 1976 American Society of Plant Biologists

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Characterization of Passive Ion Transport in Plasma Membrane Vesicles of Oat Roots 1

Heven Sze2 and Thomas K. Hodges

a Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907

The passive influx and efflux of inorganic ions across plasma membrane vesicles purified from extracts of Avena sativa roots were investigated. Uptake was measured by incubating the vesicles in a radioisotope for various times. The "loaded" vesicles were separated from the external solution by gel filtration. Efflux was measured by dialyzing the preloaded vesicles.

Ion transport was differentiated from superficial ion binding by (a) the time course of association of radioisotope with the vesicles; (b) the rate of loss of radioisotope from the vesicles; (c) the linear increase in isotope associated with the vesicles as the external concentration was increased; (d) the enhanced loss of radioisotope from the vesicles induced by Triton X-100; and (e) the low amount of isotope associated with the vesicles at low temperatures.

The plasma membrane vesicles were differentially permeable to the alkali cations with the order of decreasing permeation being K+ > Rb+ > Cs+ > Na+ > Li+. The relative transport of Rb+, Na+, and Cl– across the plasma membrane vesicles was about 1.0:0.50:0.18. The permeability coefficient (P) for Rb+ was estimated to be 0.29 ± 0.15 x 10–8 cm/sec.

ATP (and ADP) decreased the passive uptake of Rb+ into the vesicles, however, this effect did not appear to be related to the ATPase of the plasma membrane.

2 Present address: Biophysical Laboratory, Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts 02115.

1 This research was supported by National Science Foundation Grant GB-31052X. Purdue Agricultural Experiment Station Journal Paper No. 6186.






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Copyright © 1976 by the American Society of Plant Biologists