Evidence for a Ca2+ gradient across the plasma membrane of wheat protoplasts

Fluxes of Ca2+ across the plasma membrane of isolated wheat protoplasts have been measured both as net accumulation and as uptake under steady-state conditions. The ATPase inhibitors, orthovanadate and diethylstibesterol, and the divalent cation ionophore, A23187, were all found to enhance net Ca2+ accumulation by protoplasts. The uptake of Ca2+ under steady-state conditions was also stimulated by A23187 but relatively unaffected by a range of plant hormones or by red or far red light. Light treatments were compared to dark controls with protoplasts isolated from etiolated wheat. The results suggest that plant cells maintain a Ca2+ gradient across their plasma membrane but it appears not to be under phytochrome control.