MEMBRANE DEPOLARIZATION BY HEXACYANOFERRATE(III), HEXABROMOIRIDATE(IV) AND HEXACHLOROIRIDATE(IV)

Three artificial electron acceptors of different Eo and charge, hexacyanoferrate (III) (K3Fe(CN)6), hexachloroiridate (IV) (K2IrCl6), and hexabromoiridate (IV) (K2IrBr6), were compared with respect to their rate of reduction by roots of Zea mays L., the concomitant proton secretion, and to the effect on plasmalemma depolarization.It has been shown that these plasma membrane impermeable electron acceptors were reduced by a plasmalemma reductase activity. At low concentrations proton secretion was slightly inhibited, at higher concentrations, however, the rate of proton secretion was stimulated. The root cell plasmalemma showed a transient depolarization after addition of all three electron acceptors. The depolarization was concentration-dependent for the iridate complexes but not for hexacyanoferrate (III). For both iridate complexes maximum depolarization was reached at 50 μmol dm-3.A hypothetical model as an explanation of the redox dependent proton secretion will be given. © 1990 Oxford University Press.