Radial Water and Solute Flows in Roots of Zea mays: IV. ELECTRICAL POTENTIAL PROFILES ACROSS THE ROOT

Techniques have been developed for continuous recording of electricalpotential difference in maize root preparations. In this waythe continuous p.d. profile along the lateral axis of the rootcould be obtained. The features of the profile are resolvedin terms of the root morphology. Analysis of the p.d. profile indicates (a) that the phases withinthe root are electrically negative with respect to the bathingmedium, (b) that the vacuoles are positive relative to the cytoplasm,i.e. a p.d. exists across the tonoplast, (c) that all cytoplasmicphases are equipotential, which indicates a continuity withinand between the cortical and stelar symplasms, (d) that theextracellular space of the root is presumably only slightlyinfluenced by the concentration of the external medium sincethe p.d. profile within the root does not react to changes ofconcentration in the external medium, (e) that the potentialof the stelar vacuoles is negative relative to the corticalone and this is consistent with the accumulation of surplusions in the stelar vacuoles. The implications of the present findings to the elucidationof ion transport mechanism across the root are briefly discussed.