Effect of some electron donors and acceptors on redox capacity and simultaneous net H+/K+ fluxes by aeroponic sunflower seedling roots: Evidence for a CN?-resistant redox chain accessible to nonpermeative redox compounds

Abstract

Summary. Excised roots from aeroponic axenically 48 h dark-grown sunflower (HeIianthus 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 H+/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 + effiux 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 *Correspondence and reprints: U. E. FisioIogfa Vegetal, Facultad de Ciencias, Universidad de Extremadura, Campus Avda. Elvas s/n, E-06071 Badajoz, Spain. roots was extremely rapid, following similar kinetics. Thus, only the CN--resistant redox chain was involved in both cases. The redox chain inhibitor cis-ptatinum(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 ptasmalemma of in vivo roots this chain would compete for electrons with the normal CN--sensitive on...

Studying the binding of Cd2+ by ω-mercaptoalkanoic acid self assembled monolayers by cyclic voltammetry and scanning electrochemical microscopy (SECM)

“…Evidently, as the monolayer becomes negatively charged it repels the redox couple, which bears negative charge as well. It is somewhat surprising that the effect of the concentration of protons on the CV of IrCl 3À 6 commences at pH as low as pH$3.5 since it is well accepted that the dissociation constant of x-mercaptoalkanoic acids are shifted to more basic pH by 2-3 pH units, i.e., is between 8 and 9 [96][97][98][99].…”

“…The transition from positive to negative feedback ( Fig. 4(a)) occurs between pH 5.64 and 6.06; this is more than 2 pH units below the known [96][97][98][99] pK a value for such systems (pK a $ 8). This means that the transition between positive and negative feedbacks we detect with the SECM is definitely not the pH where half of the surface is protonated and half deprotonated, but much less is deprotonated during this transition.…”

Oxidative Stress Induced in Sunflower Seedling Roots by Aqueous Dry Olive-Mill Residues

“…Sunflower ( Helianthus annuus L.) seeds (Koipe, S.A., Sevilla, Spain) were surface sterilized, soaked, and germinated for 48 or 72 h in darkness at 27±1°C on filter paper moistened with sterilized distilled water [37] or ADOR non-incubated or incubated with saprobe fungi.…”

Overview of the aeroponic agriculture – An emerging technology for global food security

“…These studies reported that in an aeroponic system, plant roots quickly nourish under the available nutrients and controlled conditions. The controlled conditions include uniform nutrients concentration, EC (Electrical conductivity) and pH, temperature, relative humidity, light intensity, spraying time, spraying interval, and 100% oxygen availability in the growth chamber [93][94][95][96][97][98][99][100] . Furthermore, the detailed information about the aeroponic system is published in the previous studies of Lakhiar et al [1,2]…”