Free space uptake and influx of Ni²⁺ in excised barley roots

The free space uptake and influx of Ni 2+ ( 63 Ni 2+ ) was characterized in excised roots of 7‐day‐old, dark‐grown barley ( Hordeum vulgare L. cv. Møyar). Most of the Ni 2+ ( 63 Ni 2+ ) present in the roots after a typical experiment was removed by washing in CaCl 2+ , unlabelled NiCl 2 or EDTA solutions. The amount of loosely bound Ni 2+ increased during the first few minutes in the uptake solution, and then remained constant. A small fraction was tightly bound, probably mainly in the cell walls. Binding, both loose and tight, increased with concentration, as did influx. However, the lower the external Ni 2+ concentration, the larger was the proportion of Ni 2+ tightly bound compared with the total amount of Ni 2+ taken up. Ni 2+ influx was lowered by 85% with 2,4‐dinitrophenol, which may indicate that Ni 2+ is actively absorbed across the plasmalemma.