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Al3+-Ca2+ interactions in aluminum rhizotoxicity. I. Inhibition of root growth is not caused by reduction of calcium uptake



Al3+-Ca2+ interactions in aluminum rhizotoxicity. I. Inhibition of root growth is not caused by reduction of calcium uptake



Planta 92(1): 98-103



The cation Al3+ is toxic to plants at micromolar concentrations and can severely inhibit root growth in solution experiments. The inhibition of Ca2+ uptake in roots by Al3+ has been proposed as a possible mechanism for Al3+ and in this study the hypothesis was tested directly. Root growth and Ca2+ uptake were measured in 5-d-old seedlings of wheat (Triticum aestivum L. Thell) during exposure to Al3+ in a low-Ca2+ basal medium, and to Al3+ in the presence of added cations. Uptake of Ca2+ in whole roots and translocation to the shoot were measured using 45Ca2+, and localized measurements of net Ca2+ flux were also made at the root apex using the technique of microelectrode ion-flux estimation. Treatment with 2.64 micromolar AlCl3 in 226 micromolar CaCl2, at pH 4.5, severely inhibited root growth without affecting Ca2+ uptake. Addition of 30 mM Na+, 3 mM Mg2+ or 50 micromolar tris(ethylenediamine)cobalt(III) to this Al3+ treatment restored root growth but significantly reduced Ca2+ uptake measured over the entire root system and at the root apex. The Al3+ and Ca2+ concentrations were adjusted so that the activities of the Al3+ and Ca2+ ions were constant in all solutions (1.5 micromolar and 200 micromolar, respectively). Root growth can be severely inhibited by Al3+ concentrations that do not affect Ca2+ uptake. while the addition of ameliorating cations depresses Ca2+ uptake. These results argue against the hypothesis that Al3+ inhibits root growth by reducing Ca2+ uptake.

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Accession: 013077513

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DOI: 10.2307/23382580


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