Hexachloroiridate IV as an Electron Acceptor for a Plasmalemma Redox System in Maize Roots

Abstract

Hexachloroiridate IV, a new artificial electron acceptor for the constitutive plant plasma membrane redox system has been investigated. It appeared not to permeate through biological membranes. Due to its higher redox potential, it is a more powerful electron acceptor than hexacyanoferrate III (ferricyanide) and even micromolar concentrations are rapidly reduced. Hexachloroiridate IV increased H+ efflux over a concentration range of 0.05 to 0.1 millimolar. Lower concentrations slightly inhibited proton extrusion. Calcium stimulated both proton and electron transfer rates. Like hexacyanoferrate III-reduction, irridate reduction was inhibited by auxin. meets the criteria with the exception of (c) (during its slow decay, it releases small amounts of cyanide). Searching for other candidates, complexes were again the first choice, especially those that are substitutionally inert during reduction. HCF III shares this important property with HCI IV. The brownish substance (absorption maxima at 488 and 415 nm-see Fig. 1 Following the pioneering work of Craig and Crane (6, 7), plant plasma membrane redox systems have been investigated in vivo (2-9, 13) and in vitro (11, 12) by several groups. Two types of redox activity have been distinguished (2, 13). One is induced by iron deficiency and is present in dicots and monocots but not in grasses ('Turbo System'). The second one, the constitutive system ('Standard System') is generally present in all plant materials investigated so far. The inducible mechanism reduces ferric chelates. Other electron acceptors have been reported (13). The investigation of the constitutive system has been restricted to the use of HCF III as reduced substrate. This appeared to us to be a serious limitation in our eyes, since it could be argued that evidence for the postulation of a general electron transfer system (4,5,8) The seedlings were grown on moist paper in the dark at 26°C. Twelve intact seedlings were selected and the seeds mounted on plastic trays to allow roots to dip into a 16 ml plastic tube containing nutrient solution containing 10 mm KCl and 1 mm CaCl2.The plants were adapted to hydroculture and constant pH in the nutrient medium for 12 h at an irradiance of 150 ,umol m-2 s--'.Measurement of Net e-and H+ Efflux.

Serial Morphological Transformations of Au Nanocrystals via Post-Synthetic Galvanic Dissolution and Recursive Growth

“…Ir (3+) cations electrostatically solvated with H 2 O molecules are the major species after IrCl 3 is dissolved in neutral water. − Its high reduction potential (1.156 V vs NHE) triggers oxidative dissolution of Au nanostructures to produce nanoseeds. The dissolved Au 0 portions mainly become the AuCl 4 – complexes instead of the form of AuCl 2 – because of the unfavorable reduction potential (Au (0) + Ir 3+ + 2 Cl – ⇌ AuCl 2 – + Ir (0) , E 0 = +0.002 V).…”

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

“…The other e-acceptor tested, HCI(IV), was used to compare its effect with that of HCF(III), since it had been proposed as a better alternative to HCF(III) in the study of redox activities, because it is tess toxic (the molecule does not contain cyanide) and its reduction is controlled by the same redox system as HCF(III) (Rubinstein and Stern 1986, Ltithen and Brttger 1988, Lfithje and B5ttger 1989, Drring et al 1992. The rapid and complete reduction of HCI(IV) by the noncombined pH electrode made it impossible to measure the effect of HCI(IV) on H + efflux, as the acceptor in its oxidized form is never available to the redox systems of the roots when that electrode is present.…”

Measurements of redox activity at the plasmalemma

“…Another compound that has been used successfully to measure trans plasmaiemma redox activity is hexachloroiridate (Luthen and Bottger 1988). It has a more positive redox potential than ferricyatiide (0.87 V) and a relatively high millimolar extinction coefficient (3.68), so that it can be detected at lower concentrations.…”