Abstract: | The correlation of the effects of vitamin K3 and dicumarol (ananti-vitamin K in pharmaceutical applications) on the transplasmamembrane electrical potential difference of maize roots withthe reduction of the artificial electron acceptors hexacyanoferrate(III) or hexabromoiridate (IV) and the concomitant enhancementof acidification of the incubation medium was investigated. Vitamin K3 depolarized the plasma membrane of Zea mays L. roots,while dicumarol had no significant effect on the membrane potential.Plants treated with vitamin K3 for 30 min followed by intenserinsing showed higher reduction of hexabromoiridate (IV) thanhexacyanoferrate (III), as well as a stimulated acidificationof the incubation medium. Depolarization of the plasma membraneby hexacyanoferrate (III) or hexabromoiridate (IV) decreasedafter an incubation with vitamin K3. Pretreatment with dicumarolcaused an inhibition of hexacyanoferrate (III) reduction andmedium acidification as well as depolarization by K3. The reductionof hexabromoiridate (IV) was not affected by dicumarol pretreatment.The proton secretion associated with the reduction was slightlylowered. According to our results, it seems possible that vitaminK3 acts as an electron acceptor for the plasmalemma electrontransport system of maize roots whereas dicumarol appears toinhibit electron and proton transport. Key words: Vitamin K3, dicumarol, plasmalemma redox system, Zea mays L., membrane potential |