Electron transport across the plasmalemma of Lemna gibba G1

Abstract

Lemna gibba L., grown in the presence or absence of Fe, reduced extracellular ferricyanide with a V max of 3.09 μmol · g(-1) fresh weight · h(-1) and a K m of 115 μM. However, Fe(3+)-ethylenediaminetetraacetic acid (EDTA) was reduced only after Fe-starvation. External electron acceptors such as ferricyanide, Fe(3+)-EDTA, 2,6-dichlorophenol indophenol or methylene blue induced a membrane depolarization of up to 100 mV, but electron donors such as ferrocyanide or NADH had no effect. Light or glucose enhanced ferricyanide reduction while the concomitant membrane depolarization was much smaller. Under anaerobic conditions, ferricyanide had no effect on electrical membrane potential difference (Em). Ferricyanide reduction induced H(+) and K(+) release in a ratio of 1.16 H(+)+1 K(+)/2 e(-) (in +Fe plants) and 1.28 H(+)+0.8 K(+)/2 e(-) (in -Fe plants). Anion uptake was inhibited by ferricyanide reduction. It is concluded that the steady-state transfer of electrons and protons proceeds by separate mechanisms, by a redox system and by a H(+)-ATPase.

Influence of Temperature on Proton Secretion and Hexacyanoferrate (III) Reduction of Zea mays L. Roots

“…Rubinstein and Stern (1986), Lass et al (1986), and Marrè et al (1988) assume that cytoplasmic acidification due to enhanced electron donor oxidation and the lowered electrochemical gradient across the PM stimulate the ATPase.…”

Plasmalemma Redox Activity and H+ Extrusion in Roots of Fe-Deficient Cucumber Plants

“…We found gM CCCP to have similar effects to those of DCCD on Fe3" reduction and K+ efflux (Tables III and V), which is consistent with the above hypothesis. Inhibition of the reductase activity by CCCP has also been reported in connection with the standard system (14) and with the iron deficiency increased system (2, 4). AWANTARA ET AL.…”

“…Our results disagree with that suggestion, perhaps because we used a different e-acceptor: Fe3+-EDTA instead of ferricyanide. Lass et al (14) have found different responses in Lemna gibba depending on the e-acceptor used. When ferricyanide was added, the membrane depolarization in- Anoxia has been found to influence redox system activity.…”

“…The acidification of the medium associated with redox activity was supposed to originate from an activation of the H+-ATPase caused by the plasmalemma depolarization and cytosol acidification produced by the redox activity (14,15,21,23). However, other workers (7,16) have reported that H+ and e-are transported coupled by the redox system.…”

“…In any case, the presence of a suitable extracellular e-9 acceptor causes an acidification of the medium. The standard system features two possible linkages between e-and H' efflux: (a) both e-and H' are transported by the redox system (7,16); (b) only eare transported by the redox system, while H+ are transported by H+-ATPase (14,15,21,23). The redox system increased by iron deficiency has been suggested to transfer e-and H+ coupled across the plasmalemma and at a ratio of 2 ej/1 H+ (22); however, their results do not rule out the possibility of these H+ being transported by H+-ATPase.…”