Relationship of Transplasmalemma Redox Activity to Proton and Solute Transport by Roots of Zea mays

1986 
Transplasmalemma redox activity, monitored in the presence of exogenous ferricyanide stimulates net H + excretion and inhibits the uptake of K + and α-aminoisobutyric acid by freshly cut or washed, apical and subapical root segments of corn ( Zea mays L. cv “Seneca Chief”). H + excretion is seen only following a lag of about 5 minutes after ferricyanide addition, even though the reduction of ferricyanide occurs before 5 minutes and continues linearly. Once detected, the enhanced rate of H + excretion is retarded by the ATPase inhibitors N,N′ -dicyclohexylcarbodiimide, diethylstilbestrol, and vanadate. A model is presented in which plasmalemma redox activity in the presence of ferricyanide involves the transport only of electrons across the plasmalemma, resulting in a depolarization of the membrane potential and activation of an H + -ATPase. Such a model implies that this class of redox activity does not provide an additional and independent pathway for H + transport, but that the activity may be an important regulator of H + excretion. The 90% inhibition of K + ( 86 Rb + ) uptake within 2 minutes after ferricyanide addition can be contrasted with the 5 to 15% inhibition of uptake of α-aminoisobutyric acid. The possibility exists that a portion of the K + and most of the α-aminoisobutyric acid uptake inhibitions are related to the ferricyanide-induced depolarization of the membrane potential, but that the redox state of some component of the K + uptake system may also regulate K + fluxes.
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