Properties of plasma membrane H<sup>+</sup>-ATPase in salt-treated <i>Populus euphratica</i> callus
The plasma membrane (PM) vesicles from Populus euphratica ( P. euphratica ) callus were isolated to investigate the properties of the PM H + -ATPase. An enrichment of sealed and oriented right-side-out PM vesicles was demonstrated by measurement of the purity and orientation of membrane vesicles in the upper phase fraction. Analysis of pH optimum, temperature effects and kinetic properties showed that the properties of the PM H + -ATPase from woody plant P. euphratica callus were consistent with those from herbaceous species. Application of various thiol reagents to the reaction revealed that reduced thiol groups were essential to maintain the PM H + -ATPase activity. In addition, there was increased H + -ATPase activity in the PM vesicles when callus was exposed to NaCl. Western blotting analysis demonstrated an enhancement of H + -ATPase content in NaCl-treated P. euphratica callus compared with the control.