A possible involvement of two different systems in proton translocation was investigated by simultaneous measurement of transmembrane electron flow and proton secretion in a pH-stat combined with a redoxstat. The pH gradient between cytoplasm and apoplast is probably maintained by an H+-pumping ATPase and by a second proton extrusion system, which seems to be linked to a redox chain with NAD(P)H as electron donor. Indole acetic acid inhibits both e-and H+ efflux, but only if the 'electron draw' from the outside is not too high. The electron draw depends on the hexacyanoferrate level at the plasmalemma surface and on the Ca2+ concentration. The inhibiting effect of auxin on e-and H+ efux in the presence of hexacyanoferrate can be only detected at low levels of bivalent cations and of the artificial electron acceptor. The inhibition of e-and H+ efflux by auxin requires high oxygen levels. idants like HCF III or HCI IV will very likely impair the functions of a variety of plasmalemma proteins, including channels, cotransporters, pumps, and auxin-receptors by oxidizing sulfhydryl groups of the proteins (6). In other words, a number of important transport functions may be impaired which would alter electron and/or proton movement. (c) Alcohols can be used to increase the level of intracellular NADH through the action of the cytoplasmic alcohol dehydrogenase (6, 10, 11). Alcohols, known to be substrates for alcohol dehydrogenase such as propan-1-ol, ethanol, and butan-1-ol increase net H+ efflux immediately; propan-2-ol and methanol have no effect. This stereoselectivity and the requirement of high 02 supply for alcohol action exclude an explanation as a membrane effect. Exogenous NADH was found to increase HCF III reduction of protoplasts (21) and of intact roots (29). Komor et al. (20) have demonstrated that reduction of externally applied NAD(P)H with concomitant acidificaton in the apoplast is without involvement of transmembrane steps. An independence of transplasma membrane proton gradient from NAD(P)H-HCF III oxidoredtction in maize root microsoms was described (24). We therefore avoided addition of NAD(P)H and tried to distinguish between H+-pumping ATPase and redoxchain-linked proton extrusion by the use of different 02 pressures as the ATP generating system and the plasmalemma NAD(P)H oxidase have very different Km values for 02.The aim of the present paper is to investigate the influence of hormones and other effectors on the proton extrusion and its possible linkage to transmembrane electron transfer. MATERIALS AND METHODS

No abstract

Responses of potassium hexacyanoferrate (111) [HCF(III)] reduction and net proton secretion by

No abstract