Effect of the Shoot on the Transmembrane Potentials of Root Cortical Cells of Sunflower

Abstract

Transmembrane potentials (PD) of root cortical cells were measured between the vacuole and the external solution while the roots remained attached to the plants. External solution con centration was varied by using a range of dilutions of a balanced nutrient solution. In all cases the PD was more negative than that due to diffusion alone indicating the presence of an elec trogenic or metabolically derived component. This component contributed an additional —80 mV to the PD and was relatively independent of the external solution concentration. The metabolic component was eliminated by metabolic inhibitors, placing the shoot in darkness, ringing the phloem, or severing the rootlet from the shoot ; it was restored again by removing the inhibitor, by light, or, in the case of severance, by adding 25 ml sucrose to the medium. The magnitude of the electrogenic component of the PD was dependent on the antecedent light intensity in a way reminiscent of translocation itself.