Modifying effects of a non-toxic level of aluminium on phosphate fluxes and compartmentation in root cortex cells of intact ryegrass seedlings

From compartmental analysis of 32P elution measurements, concentrations and fluxes of phosphate were estimated for root cortical cells of intact Lolium perenne L. plants, when in complete nutrient solution containing 0.1 mol m-3 phosphate with and without 37 mmol m-3 Al during loading and elution. Failure of the data, when plotted as ct. min-1 remaining in the tissue as a function of time, to meet the criteria for first order kinetics led to a discussion of the relative importance of transport to the shoot, assimilation, and complexation in the vacuole, in causing this discrepancy. It was concluded that complexation was the most important factor. Transformation of the data to meet the criteria for first order kinetics gave corrected values for compartmental concentrations and fluxes of phosphate, and estimates of the size of the otherwise unresolved slowly exchanging compartment within the vacuole equated with condensed phosphate. In the control this was 2.5 mol m-3 P but in Al treatments a much larger amount of phosphate was complexed with Al (6.5 mol m-3 P). Phosphate transport to the shoot was unaffected by Al. Instead, levels of Al, common in solution in upland soils, sequestered in the root vacuoles quantities of phosphate significant for stressing the phosphate economy of nutrient-poor grassland.