Comparison of Plasma Membrane ATPase from Salt-treated and Salt-free Grown Plantago maritima L.

Abstract

Summary Plasma membrane ATPase from the halophyte Plantago maritima L. grown under saline and non-saline conditions was analysed in the native and solubilized state and compared to the solubilized enzyme from the glycophyte Plantago lanceolata L. Plasma membranes from leaves and roots were isolated using an aqueous two-phase system formed by polyethylene glycol and dextran. These membranes contain a phosphatase activity that shows high specificity for ATP, is inhibited by orthovanadate and N,N′-dicyclohexylcarbodiimide and reveals a Km of 0.18 mM for (MgATP)2− when analysed in roots of salt-treated P. maritima (200 mM NaCl). By the use of a stepwise washing and solubilization method it was possible to solubilize the activity in the presence of 1 % lysophosphatidylcholine in preparations from roots and leaves of P. lanceolata and of salt-treated and control plants of P. maritima. In all cases, contamination by unspecific phosphatase could be drastically reduced or completely excluded by the washing and solubilization procedure. The enzymes from all plants tested showed very similar characteristics (i.e. pH-dependence, kinetics, substrate specificity). It is concluded that salt treatment does not affect the properties of the plasma membrane ATPase and that the role of this enzyme in ion flux control in the halophyte is merely limited to the energization of the plasma membrane for secondary active transport.