Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 55, Issue 401, Pages 1343-1349Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erh155
Keywords
calcium; diphenylene iodonium; NAD(P)H-loaded vesicles; plasma membrane; transmembrane electron transport; Zea mays
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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 muM calcium decreased HCF III reduction up to 66%, while pre-incubation with 200 muM warfarin or diphenylene iodonium inhibited transmembrane electron transport only weakly. Fe3+-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.
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