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Membrane potential depolarization of root cap cells precedes aluminum tolerance in snapbean

Olivetti, G.P., Cumming, J.R., Etherton, B.
Plant physiology 1995 v.109 no.1 pp. 123-129
Phaseolus vulgaris, cultivars, metal tolerance, aluminum, ionic strength, nutrient solutions, potassium, cations, membrane potential, phytotoxicity, resistance mechanisms, line differences
Two cultivars of snapbean (Phaseolus vulgaris L.) that differ in their sensitivity to aluminum (Al) exhibited significantly different electrical responses in root cap cells when exposed toAl. Membrane potentials of the Al-tolerant cultivar Dade rapidly and significantly depolarized upon exposure to increasing Al concentrations, to a maximum depolarization of 55 mV at 150 micromolar AlCl3. In contrast membrane potentials of the Al-sensitive cultivar Romano were only slightly depolarized by increasing Al concentrations, with none of the recorded depolarizations being statistically different from controls. Further experiments with 100 micromolar AlCl3 suggested that Al significantly decreased passive potassium efflux in Dade root cap cells but not in those of Romano. The addition of the K+ channel blocker tetraethylammonium chloride depolarized the membrane potential of Dade by 69 mV, in 0.1 mM K+, but did not change the membrane potential of Romano. At higher K+ concentrations, tetraethylammonium chloride-induced depolarizations were decreased in Dade and small hyperpolarizations were found in Romano. Experiments with cyanide suggested that the membrane potential in Romano is more electrogenic in origin than in Dade. These data are consistent with a model in which Al reduces K+ efflux channel conductance in Dade root cap cells, but does not affect K+ efflux channel conductance in Romano.