Active calcium transporters in isolated membranes of wheat root cells

Plant endomembranes carry both primary and secondary ATP-dependentCa²⁺ transporters, but conflicting results have been obtainedas to their subcellular localization and means of regulation.This study describes how these transporters can be given a respectivecharacterization, by proper choice of pH and inhibitors/activators,even under conditions when they cannot physically be separatedfrom each other. The characterization was done with a lightendomembrane fraction from the outer 1–1.5 cm of wheatroot tips (Triticum aestivum L.), free from plasma membranes.The endomembrane secondary active ATP-driven Ca²⁺ transportwas totally inhibited by bafilomycin, was increased several-foldby oxalate and had a pH optimum at 7.4, The primary active ATP-dependentCa²⁺ transport was inhibited by vanadate and erythrosin B, wasnot increased by oxalate, and had a relatively lower pH optimum(