title: Transmembrane electron transport in sealed and NAD(P)H-loaded right-side-out plasma membrane vesicles isolated from maize (Zea mays L.) roots.
abstract: Electron transport across plasma membranes has been observed in vivo in several plant species and tissues after the application of ferricyanide (hexacyanoferrate III, HCF III). In the present work, a transmembrane electron flow was demonstrated in sealed and NAD(P)H-loaded right-side-out (apoplastic-side-out) plasma membrane vesicles isolated from maize (Zea mays L.) roots. HCF III was reduced at a rate of up to 126 nmol min(-1) mg(-1) protein by NADPH-loaded vesicles, while reduction rates with NADH-loaded vesicles were several-fold lower. Coincident with the reduction of HCF III, NAD(P)H oxidation was observed inside the vesicles. The dependence of reduction on K+ indicated an electrogenic transmembrane electron flow. Application of 100 microM calcium decreased HCF III reduction up to 66%, while pre-incubation with 200 microM warfarin or diphenylene iodonium inhibited transmembrane electron transport only weakly. Fe(3+)-EDTA was not reduced significantly by NADPH-loaded plasma membrane vesicles, whereas XTT was reduced at a rate of 765 pmol min(-1) mg(-1) protein. The results suggested a major function for NADPH in transmembrane electron flow and were discussed in conjunction with in vivo experiments.
authors.affiliation: Universität Hamburg, Biozentrum Klein Flottbek und Botanischer Garten, Ohnhorststrabetae 18, D-22609 Hamburg, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Menckhoff
authors.forename: Sabine
authors.initials: S
authors.lastname: Lüthje
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D004492:Edetic Acid / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D005292:Ferricyanides / Q000378:metabolism / Q000494:pharmacology; D009249:NADP / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology; D018517:Plant Roots / Q000502:physiology*; D022161:Transport Vesicles / Q000187:drug effects / Q000502:physiology*; D014859:Warfarin / Q000494:pharmacology; D003313:Zea mays / Q000502:physiology*
chemical_list: D005292:Ferricyanides; D009861:Onium Compounds; C007931:hexacyanoferrate III; D009249:NADP; D014859:Warfarin; C007517:diphenyleneiodonium; D004492:Edetic Acid; D002118:Calcium