Properties of native and solubilized plasma membrane ATPase from the halophyte Plantago crassifolia, grown under saline and non-saline conditions

Plasma membrane ATPase from the mediterranean halophyte Plantago crassifolia Forskal was analysed in the native and solubilized state. The enzyme revealed a broad pH optimum at 6.3 when analysed in plasma membrane preparations from roots. A further purified preparation of leaf plasma membrane ATPase was obtained by a three-step solubilization method. Final solubilization of the enzyme was achieved with 1% lysophosphatidylcholine. This enzyme showed a narrow pH optimum at 6.3, inhibition by vanadate, fluoride and N,N'-dicyclohexylcarbodiimide and a high specificity for ATP. The preparations contained a major polypeptide of 107 kDa. None of the parameters analysed in this enzyme changed upon transfer to saline conditions, although the leaves accumulated Na⁺ and Cl⁻ and an enhanced formation of the compatible organic osmoticum, sorbitol, was detected. It is concluded that at least in this halophyte, the plasma membrane ATPase undergoes no changes during the physiological adaptation of the plant to a saline environment.