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Calcium fluxes at the root of aluminium responses A key issue in land use for agriculture is the response of plants to soil-borne toxic substances. In acid soils, for example, aluminium toxicity may be a problem, especially if the soils are derived from aluminiumrich minerals. Plants vary considerably in their response to aluminium ions and it is of interest to know why, for example, rye (Secale cereale) is much less sensitive to aluminium than wheat (Triticum aestivum). It has been suggested that disruption of calcium fluxes may be a primary or at least an early event in aluminium toxicity. Considering the roles of calcium in signal transduction and in cell growth and division, it would indeed be unsurprising if disruption of calcium fluxes led to an inhibition of growth. To examine further the relationship between aluminium toxicity and calcium physiology, Ma et al. (University of Western Australia, pp. 241-244) have studied the timing of different aspects of the response to aluminium in intact roots of rye. Roots exposed to 100 [mu]M aluminium show an increase in cytosolic calcium concentration within 10 min (as measured by the fluorescence of a calcium-sensitive dye, preloaded into the root cells). Inhibition of root elongation was apparent within 1 h and by 6 h the rate was one-third of the control rate. Aluminium at 50 [mu]M had much less effect; for example, there was no significant effect on root elongation rate for at least 5 h. Thus, effects on calcium fluxes occur very early in exposure to toxic aluminium concentrations and precede effects on root growth, consistent with the view that disruptions to calcium physiology lead to growth inhibition. However, we are still some way from understanding how aluminium induces calcium release to the cytosol or why it takes higher concentrations of aluminium to induce these changes in rye than in wheat.
Professor J.A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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