Involvement of plasma membrane redox system in the generation of trans-root electrical potential difference in excised maize root.

Possible involvement of the plasma membrane bound redox system in the generation of the trans-root electrical potential difference (TRP) arising across 8 day old maize (Zea mays L. hybrid ZPSC704) roots was studied. Excised roots were exposed to artificial impermeable electron acceptors (potassium hexacyanoferrate III and potassium hexachloroiridate IV) in external solution, and TRP response, oxygen consumption rate, proton efflux and reduction of the electron acceptors were analyzed. The effect of hexacyanoferrate III (HCF III) was tested at three concentrations (0.1; 0.5 and 1.0 mmol/l), and hexachloroiridate IV (HCI IV) in the concentration range 10(-7)-5.10(-4) mol/l. Both electron acceptors depolarized the trans-root potential, an order of magnitude lower concentrations of hexachloroiridate producing a much more rapid depolarization of greater magnitude. The roots had a higher capacity to reduce 0.1 mmol/l hexachloroiridate than 1 mmol/l hexacyanoferrate. Also, an increased level of acidification induced by HCI IV than HCF III could be observed. The rate of oxygen consumption showed an increase of about 20% in both cases. These results prove that electron transplasma membrane transport process(es) contribute to the total trans-root electrical potential difference across an excised maize root.