Membrane electrical potentials in the cortex and stele of corn roots.

This paper reports the results of experiments which are of interest concerning the relationship of root cortex and stelar transmembrane electrical potentials to ion transport into the xylem vessels. Specifically, the electrical potential difference between cells in the cortex and stele of corn root segments and the external solution is reported. It has been suggested (6, 10) that if cells of the cortex or stele participate in ionic delivery to the vessels-as with the symplast theory (1, 5), for which there is considerable supporting evidence (1l)-then knowledge of the PD2 between cortical and stelar parencyhma cells and the xylem vessels would be important. Previous studies of this nature have considered only the PD between the xylem exudate and the external solution (2-4, 14, 15). The results reported here are also of interest regarding the theory that inner root cells leak ions into the vessels (11, 12). Leaky inner root cells should be at a lower (less negative) potential than outer cortical cells, and the PD of the inner cells should change dramatically in response to changes of external ion concentration; PD measurements are, therefore, reported at two concentrations of external K+.