Cadmium transport across tonoplast of vesicles from oat roots. Evidence for a Cd2+/H+ antiport activity.
Cadmium accumulates in the vacuole of plant cells, but the mechanism driving its transport across the vacuole membrane is not understood. Here we present evidence for Cd2+ transport via a Cd2+/H+ antiport activity into tonoplast-enriched vesicles isolated from oat roots. Experimentally, accumulation of Cd2+ into vesicles could be driven by delta pH generated by either V-type ATPase or artificially using nigericin to exchange K+ and H+ in K(+)-loaded vesicles. When tonoplast-enriched vesicles were separated on a linear sucrose gradient, NO3(-)-sensitive ATPase, total MgATPase, and delta pH-dependent Cd2+ transport equilibrated at 1.11 g/ml, the density of tonoplast membrane. Cd2+ accumulation in vesicles was accompanied by efflux of protons in a Cd2+ concentration-dependent manner characteristic of an antiport activity. The delta pH-dependent Cd2+ accumulation process showed saturation kinetics with a Km(app) of 5.5 microM. Thus the process is a candidate for transport of Cd2+ from the cytoplasm to the vacuolar sap under conditions of low as well as high Cd2+ exposure.
Agronomy Department, University of Kentucky, Lexington 40546-0091.
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D000251:Adenosine Triphosphatases / Q000378:metabolism*; D017920:Antiporters; D001692:Biological Transport; D002104:Cadmium / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D002523:Edible Grain / Q000201:enzymology / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009550:Nigericin / Q000378:metabolism; D015388:Organelles / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism
D017920:Antiporters; D002352:Carrier Proteins; D002104:Cadmium; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D006859:Hydrogen; D000251:Adenosine Triphosphatases; D009550:Nigericin; D011188:Potassium