Trans-root potential, xylem pressure, and root cortical membrane potentialof 'low-salt' maize plants as influenced by nitrate and ammonium

Upon addition of nitrate and ammonium, respectively, to the bath of intact 'low salt' maize plants, the cortical membrane potential and the trans-root potential changed in a similar and synchronous way as revealed by applying conventional microelectrode techniques and the xylem pressure-potential pr obe (Wegner & Zimmermann 1998), Upon addition of nitrate, a hyperpolarizati on response was observed which was frequently preceded by a short depolariz ation phase. In contrast, addition of ammonium resulted in an overall depol arization response both of the cortical membrane potential and the trans-ro ot potential. The nitrate-induced hyperpolarization response and the depola rization following the addition of ammonium were concentration-dependent. The data suggest that a tight electrical coupling exists between the cellul ar and tissue level in the root of the intact plant and that the resistance of the cellular (symplastic) space is much less than the resistance of the apoplast.