Correlation between ion fluxes and ion-stimulated adenosine triphosphatase activity of plant roots.

The energy-dependent influx of Rb(+) into excised roots of corn, wheat, and barley has been determined and compared to the Rb(+)-stimulated ATPase activity of membrane fractions obtained from root homogenates of these species. The external Rb(+) concentrations studied were in the range of 1 to 50 mm. The ratio of Rb(+) influx/Rb(+)-stimulated ATPase was approximately 0.85 and was nearly constant for all the species and Rb(+) concentrations studied. The correlation coefficient for Rb(+) influx versus Rb(+)-activated ATPase was 0.94. The results support the concept that ATP is the energy source for ion transport in roots and that an ATPase participates in the energy transduction process involved in energy-dependent ion transport.