title: Inhibition of trans-membrane hexacyanoferrate III reductase activity and proton secretion of maize (Zea mays L.) roots by thenoyltrifluoroacetone.
abstract: Intact plants can reduce external oxidants by an appearingly trans-membrane electron transport. In vivo an increase in net medium acidification accompanies the reduction of the apoplastic substrate. Up to now, several NAD(P)H dehydrogenases, b-type cytochromes, and a phylloquinone have been identified and partially purified from plant plasma membranes. The occurrence of a quinone in the plasma membrane of maize roots supports the hypothetical model of a proton-transferring redox system, i.e., an electron transport chain with a quinone as mobile electron and proton carrier. In the present study the trans-membrane electron transport system of intact maize (Zea mays L.) roots was investigated. Flow-through and ionostat systems have been used to estimate the electron and proton transport activity of this material. Application of 4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dione (thenoyltrifluoroacetone) inhibited the reduction of ferricyanide in the incubation solution of intact maize roots up to 70%. This inhibition could not be washed off by rinsing the roots with fresh incubation medium. The acidification of the medium induced after ferricyanide application was inhibited to about 62%. The effects of thenoyltrifluoroacetone on proton fluxes in the absence of ferricyanide have been characterized in a pH-stat system. The net medium acidification by maize roots was inhibited up to 75% by thenoyltrifluoroacetone in the absence of ferricyanide, while dicumarol inhibited net acidification completely. The inhibition of H(+)-ATPase activity was estimated with plasma membrane vesicles isolated by phase partitioning and treated with 0.05% (w/v) Brij 58. ATP-dependent proton gradients and Pi release were measured after preincubation with the effectors. The proton pumping activity by those plasma membrane vesicles was inhibited by dicumarol (53.6%) and thenoyltrifluoroacctone (77.8%), while the release of Pi was unaffected by both inhibitors.
authors.affiliation: Institut für Allgemeine Botanik, Universität Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Federal Republic of Germany.
authors.forename: O
authors.initials: O
authors.lastname: Döring
authors.forename: S
authors.initials: S
authors.lastname: Lüthje
mesh_terms: D002462:Cell Membrane / Q000201:enzymology* / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D001728:Dicumarol / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005292:Ferricyanides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010084:Oxidation-Reduction; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D011522:Protons; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology*; D014475:Uncoupling Agents / Q000494:pharmacology; D014859:Warfarin / Q000494:pharmacology; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005292:Ferricyanides; D011522:Protons; D014475:Uncoupling Agents; C007931:hexacyanoferrate III; D013804:Thenoyltrifluoroacetone; D014859:Warfarin; D001728:Dicumarol; D009247:NADH, NADPH Oxidoreductases; C014227:ferricyanide reductase