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1.
Summary Excised roots from aeroponic axenically 48 h dark-grown sunflower (Helianthus annuus L.) seedlings showed redox activities, being able to oxidize/reduce all the exogenously added electron donors/acceptors, that affected the H+/K+ net fluxes simultaneously measured in the medium. Trials were performed with in vivo and CN–-poisoned roots; these showed null+/K+ net flux activity but still oxidized/reduced all the e– donors/acceptors tested except NADH. NADH enhanced the rate of H+ efflux by in vivo roots, otherwise not changing any of the normal flux kinetic characteristics, suggesting that NADH donates e– and H+ to the exocellular NADH oxidoreductase activity of a CN–-sensitive redox chain in the plasmalemma of the root cells. K+ influx was not affected, probably because the NADH concentration was not very high. The e– donor HFC(hexacyanoferrate)(II) activated the H+ efflux in a very different way: maximum H+ efflux rate was maintained, but both the maximum rate plateau and the optimal pH range were extended, and hence the total H+ efflux was significantly enhanced. At the same time, the K+ influx was doubled. The different H+-efflux kinetics, together with the small but significant HCF(II) oxidation by CN–-poisoned roots, were taken as evidence that, besides the CN–-sensitive redox chain, an alternative CN–-resistant redox chain in the plasmalemma was involved in HCF(II) oxidation. The effect of the oxidized form HCF(III) on H+ and K+ fluxes was the opposite to that described for HCF(II), but the other H+ efflux kinetic characteristics were similar (the maximum rate plateau was extended so that total H+ efflux equaled that of the controls). It is proposed that HCF(III) accepts e– only from the alternative CN–-resistant redox chain. We could not measure the effect of HCI(hexachloroiridate)(IV) on H+ efflux, as the pH electrodes alone quickly reduced the compound. HCI(IV) promoted a rapid transitory K+ efflux, followed by recovery of K+ influx. The HCI(IV) reduction by in vivo or CN–-poisoned roots was extremely rapid, following similar kinetics. Thus, only the CN–-resistant redox chain was involved in both cases. The redox chain inhibitor cis-platinum(II) annulled ion fluxes in the presence of both NADH and HCF(III), and later even inverted them (a small H+ influx down the gradient would induce K+ efflux). Cis-platinum(II) did not affect HCF(III) reduction by in vivo roots, and only slightly depressed that by CN–-poisoned roots. Overall, the effects of the exogenously added e– donors/acceptors tested were consistent with the existence of a CN–-resistant redox chain in the plasmalemma of the root cells which would donate/accept e– even when the H+ and K+ fluxes were annulled by CN– or even inverted by cis-platinum(II) treatments. Thus, in the plasmalemma of in vivo roots this chain would compete for electrons with the normal CN–-sensitive one, as in plant mitochondria. The effects on the K+ flux were consistent with the current hypothesis that this contributes to counteracting the changes in membrane potential caused by redox activities and the H+ flux induced by the different redox compounds tested.Abbreviations cis-Pt(II)
cis-platinum(II) diammine dichloride
- HCF(II)
hexacyanoferrate(II) (or ferrocyanide) potassium salt
- HCF(III)
hexacyanoferrate(III) (or ferricyanide) potassium salt
- HCI(IV)
hexachloroiridate(IV)
- PMOR
plasmalemma oxidoreductase complex 相似文献
2.
Liñero Olaia Cornu Jean-Yves de Diego Alberto Bussière Sylvie Coriou Cécile Thunot Stéphane Robert Thierry Nguyen Christophe 《Plant and Soil》2018,424(1-2):435-450
Plant and Soil - This study investigated the possible source organs delivering several trace elements to seeds (root uptake versus net remobilization), by studying changes in biomass and element... 相似文献