Effects of Ni 2+ on proton extrusion and related transport processes and on the transmembrane electrical potential in maize roots

Abstract

The presence of Ni 2+ in the incubation medium of maize roots induces an early and significant enhancement of the rate of proton extrusion, an inhibition of K + and leucine uptake and a slight stimulation of 3- O-methylglucose (3- O-MG) and phosphate uptake. The uptake of Ni 2+ is accompanied by a rapid depolarization of the trans-membrane electrical potential (PD). At the 1-mM concentration, both the uptake and the depolarizing effect of Ni 2+ are quantitatively similar to those of K +. These data suggest that the primary effect of Ni 2+ is the depolarization of PD, which would activate H + extrusion; the other transport phenomena would thus be differently influenced by the changes of the electrical and H + gradients. Some probable secondary consequences of Ni 2+ accumulation in the tissue are also discussed.