Tonoplast ATPase proton pumps in wheat roots

A crude membrane preparation isolated from wheat (Triticum aestivum L. cv. Winalta) roots was separated by differential and sucrose density gradient centrifugation into three fractions which were analysed using sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE). One of these fractions is enriched in nitrate-sensitive ATP ase activity and contains nitrate-sensitive and vanadate-insensitive, ATP-dependent proton-translocating activity. This presumptive tonoplast(TP)-enriched fraction also contains a 68–70-kDa polypeptide which strongly cross-reacts with antiserum developed against an amino-terminus peptide of the 70-kDa subunit of the carrot (Daucus carota) L. vacuolar ATPase. We have also found that AlF4− (fluoroaluminate), a reputed G protein activator, strongly inhibits vanadate-sensitive ATPase activity, but has relatively little effect on the nitrate-sensitive ATPase activity in wheat root membranes.