Aluminium Effects on Vacuolar Phosphorus in Roots of Beech ( Fagus sylvatica L.)

Abstract

Summary Plants of beech ( Fagus sylvatica L.) were grown on nutrient solutions with various concentrations of phosphate (0, 0.01, 0.1, 1.0 mM) and aluminium (0, 0.1, 1.0 mM) and at low pH (usually 4.2). About half of the supplied Al occurred as Al 3+ under these conditions. The vacuolar inorganic phosphate concentrations, [P] vac , of excised fine roots were determined by 31 P NMR. In roots of plants treated with 0.1 mM AlCl 3 , [P] vac did not change over a period of 21 days. In contrast, plants treated with 1.0 mM AlCl 3 for about one day (18–29 h) generally contained somewhat higher [P] vac in the roots than did control plants. Longer treatments (3–21 days) at the high Al level caused a continuously decreasing [P] vac in the roots; [P] vac was 22 % of control after 21 days. In the presence of 1.0 mM AlCl 3 , plants with different P status showed about the same relative decrease of [P] vac . After transfer of control plants to a P- and Al-free nutrient solution, [P] vac , of roots decreased in a manner similar to that for the 1.0 mM Al treatment. The results show that exposure to 1.0 mM Al initially increases [P] vac , apparently due to a decrease in metabolic fixation of inorganic phosphate in the cytoplasm and subsequent transfer of inorganic phosphate to vacuoles. Al-P complex formation in substrate and root cell walls or specific effects on cell membranes may inhibit phosphate influx. Then, within 2–3 weeks most of the P reserves in the vacuoles are used to maintain growth. Our results are discussed in relation to effects by aluminium on P nutrition of trees growing on acid soils.