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Potassium hydrogen exchange transport in plant membrane vesicles is evidence for potassium transport

Plant Science (Shannon) 41(3): 161-168
Potassium hydrogen exchange transport in plant membrane vesicles is evidence for potassium transport
A tonoplast- and a plasma membrane-enriched vesicle fraction [from zucchini, Cucurbita pepo] both active in H+ transport were prepared with sequential centrifugation on a sucrose step gradient and a glycerol density gradient. At pH 6.5 no differential influence of monovalent cations on H+ transport (.DELTA.pH) was observed whereas at higher pHout a cation-specific decrease of apparent H+ transport activity was observed with the order of apparent activities being Li+ = choline+ > Cs+ > Rb+ > Na+ = K+. The apparent passive proton permeabilities in the presence of these cations increased in the order choline+ = Cs+ < Li+ < Rb+ < Na+ = K+. Allowing electroneutral H+/K+ exchange with nigericin uncoupled the .DELTA.pH but increased the steady state membrane potential. The steady state membrane potential without nigericin at pH 6.5 or at pH 8.0 was highest with K+ as compared to the other alkali cations. This shows that the K+-specific decrease of .DELTA.pH and the increase of the apparent passive proton permeability in the presence of K+ was due to electroneutral K+/H+ exchange transport which might indicate the presence of a K+/H+ antiporter in native plant membranes.

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Accession: 006156209

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