Identification of H+/Ca2+ Antiporter in Barley Root Plasma Membrane

On the basis of two types of calcium transport system detected in the barley root plasmamembrane,the mechanisms of the calcium transport have been further studied.Ionophore CCCP has beenfound to inhibit Mg-dependent calcium transport by 20%.In contrast,Mg-independent calcium trans-port is insensitive to CCCP.The Mg-dependent calcium transport following the collapse of Hgradientacross the plasma membrane could be driven by the Hgradient either set up by ATP or imposed artificially.Any relation between Mg-independent calcium transport and Hgradient has not been observed.Theseresults indicate that Mg-dependent calcium transport is accompanied by the decrease of Hgradient,andMg-independent calcium transport has nothing to do with the Hgradient.It is therefore suggested thatthe calcium transport across the barley root plasma membrane is driven by ATPase that is independent ofMg,and H/Caantiporter that is dependent on Mg.