The effects of aluminum on the influx of calcium, potassium, ammonium, nitrate, and phosphate in an aluminum- sensitive cultivar of barley (Hordeum vulgare L.)

The mechanism by which aluminum interferes with ion influx is not known. In this study, the effects of aluminum on the influx of the cations calcium, potassium, and ammonium and the anions nitrate and phosphate were measured in an aluminum-sensitive cultivar of barley (Hordeum vulgare L). Aluminum (100 micromolar) was found to inhibit the influx of the cations calcium (69%), ammonium (40%), and potassium (13%) and enhancing the influx of the anions nitrate (44%) and phosphate (17%). Aluminum interfered with the binding of the cations in the cell wall by the same order of magnitude as their respective influxes, whereas phosphate binding was strongly enhanced. The results are consistent with a mechanism whereby aluminum binds to the plasma membrane phospholipids, forming a positively charged layer that influences ion movement to the binding sites of the transport proteins. A positive charge layer would retard the movement of cations and increase the movement of anions to the plasma membrane in proportion to the charges carried by these ions.