Hexachloroiridate IV as an electron acceptor for a plasmalemma redox system in maize roots

Hexachloroiridate IV, a new artificial electron acceptor for the constitutive plant plasma membrane redox system has been investigated. It appeared not to permeate through biological membranes. Due to its higher redox potential, it is a more powerful electron acceptor than hexacyanoferrate III (ferricyanide) and even micromolar concentrations are rapidly reduced. Hexachloroiridate IV increased H+ efflux over a concentration range of 0.05 to 0.1 millimolar. Lower concentrations slightly inhibited proton extrusion. Calcium stimulated both proton and electron transfer rates. Like hexacyanoferrate III-reduction, irridate reduction was inhibited by auxin.