Membrane fluxes and comparative toxicities of aluminium, scandium and gallium |
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Authors: | Reid RJ; Rengel Z; Smith FA |
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Abstract: | Measurements were made of the membrane fluxes and toxicitiesof three cations with trivalent forms, Al, Ga and Sc, in internodalcells of the giant alga Chara corallina. With this species itwas possible to separate the cell wall from the cell contentsto obtain membrane fluxes which were not complicated by adsorptionof cations to the cell wall. Net uptake of Al was low, approximately1.5 pmol m2 s1, compared to the influxes of thedivalent cation 45Ca of 82 pmol m2 s1 and themonovalent cation 22Na of 1100 pmol m2 s1 at thesame external concentration. Traditional desorption methodsfor removing cell wall cations were found to be relatively ineffectivein the case of trivalent cations and, consequently, influx measuredwithout separating the cell wall component would greatly overestimatethe true membrane flux, possibly by several orders of magnitude.Al, Ga and Sc all inhibited growth at 20 mmol m3 at pH4.4. Toxicity decreased in the order Sc>Al>Ga. Sc andAl were also toxic to mature non-growing cells. Influx of 46Scincreased with increasing pH, consistent with membrane permeationby hydroxy Sc rather than Sc3+. However, Sc was more toxic atlow pH where Sc3+ was the dominant species and where influxwas low and binding to cell walls was high. These results argueagainst Sc acting intracellularly and favour a toxicity mechanismwhich is initiated extracellularly. Key words: Aluminium toxicity, trivalent cations, Chara corallina, scandium influx, gallium |
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