Rapid Hormone-induced Hyperpolarization of the Oat Coleoptile Transmembrane Potential

Abstract

The effects of the plant growth substances indoleacetic acid (IAA) and fusicoccin on the transmembrane potential of Avena coleoptile cells (at 27-29 C) were studied. Fusicoccin caused hyperpolarization of the membrane potential which started after a lag of less than 20 seconds, and which on average reached -49 my at an external K+ concentration of 1 mm and -75 my at 0.1 mm K+. IAA caused a hyperpolanzation of -25 my starting after a lag of 7 to 8 minutes. These results suggest that fusicoccin and IAA both activate electrogenic H+ extusion.The growth-promoting compounds IAA and fusicoccin (FC)4 cause a variety of plant cells to excrete protons (2-4, 15, 19).The resulting lowered pH of the wall is believed to induce wall loosening and thus cell elongation (8,12,20). These compounds also stimulate K+ uptake, although the effect of FC is much greater than that of IAA (5).In the absence of hormones 02c+ + 0h+ should be equal to 0°K+ + 0lt+ where 0D+ refers to the total K+ influx, both passive and active, and the other symbols are for K+ efflux and for the influx and efflux of H+. If auxin or FC stimulates 0K+ and 0l,+ equally, there will be no change in the membrane electropotential and the process can be described as an electroneutral K+/H+ exchange, but if 0°+ exceeds 0K+ there will be a hyperpolarization of the membrane potential and the proton excretion can be called electrogenic. With both FC and IAA, proton excretion from oat coleoptiles appears to occur at a more rapid rate than K+ uptake (5). We would expect that both FC and IAA should cause a hyperpolarization of the membrane potential starting at the same time as the H+ excretion.Some measurements of the effects of IAA and FC on PD exist, but the results have been inconclusive. Both hyperpolarization (9) and depolarization (14) of the PD in response to IAA have been found for Avena coleoptiles; in the latter case, the measurements were made hours after application of the hormones. FC causes rapid hyperpolarization in squash cotyledons (16), barley roots (18), and corn roots (7), but its effect on Avena coleoptiles has not been determined. ' In this study, we have examined the time course of IAA and FC-induced changes in the PD and have shown both compounds induce hyperpolarization which appears to be related to the proton excretion found earlier. MATERIALS AND METHODSThe plant material consisted of 15-to 20-mm sections cut from 25-to 32-mm long coleoptiles of Avena sativa, cv. Victory. The plants were grown and the sections were harvested as described earlier (1), except that the manipulations and all experimental procedures were carried out under fluorescent illumination. After removal of the leaves, the sections were peeled (19) and before use were preincubated for a minimum of 1 hr and a maximum of 3 hr in a solution containing 1 mm MES-tris (pH 6), 0.1 mM CaC12, and 0.1 or 1 mm KCI.Transmembrane potential differences were measured with pairs of 3 M KCl-filled glass microelectrodes and the electronic equipment described earlier (10). Segment...

Cellular responses to naphthoquinones: juglone as a case study

“…2), (2) enhancement of proton extrusion, as compared to IAA-free medium (Fig. 3), and (3) hyperpolarization of the membrane potential (Table 1), are in good agreement with results obtained by other investigators (Cleland et al 1977;Kutschera and Schopfer 1985;Felle et al 1991;Lüthen et al 1990;Rücke et al 1993;Keller and Van Volkenburgh 1996;Burdach 2002, 2007;Kurtyka et al 2011). There is no doubt that plasma membrane hyperpolarization observed in the presence of IAA is a consequence of stimulated proton extrusion through H ?…”

“…There is no doubt that plasma membrane hyperpolarization observed in the presence of IAA is a consequence of stimulated proton extrusion through H ? -ATPase (Cleland et al 1977;Lohse and Hedrich 1992;Rücke et al 1993;Hedrich et al 1995).…”

“…Activation of the proton pump by auxin also causes hyperpolarization of the membrane potential and activation of voltage-dependent, inwardly rectifying K ? channels, activity of which contributes to water uptake necessary for cell expansion (Cleland et al 1977;Keller and Van Volkenburgh 1996;Philippar et al 1999;Becker and Hedrich 2002;Burdach 2002, 2007).…”

Vanadate inhibition of auxin-enhanced H + secretion and elongation in pea epicotyls and oat coleoptiles

“…Hager et al (2) first proposed that auxin activates a plasma membrane ATPase which functions as a proton pump. Auxin can induce membrane hyperpolarization (13,14) and its action is antagonized by inhibitors of ATP synthesis (8,9,15), observations consistent with the operation of an electrogenicq proton pump that utilizes ATP. However, there is no direct evidence for the participation of an ATPase in auxin-induced acidification.…”

Phytochrome Modifies Blue-light-induced Electrical Changes in Corn Coleoptiles

“…Grahm (7) measured external voltages on coleoptiles using surface electrodes and found that voltage changes following unilateral irradiation occurred after the arrival of auxin at the measured sites. More recently, Cleland et al (3) showed that exogenously applied auxin hyperpolarized oat Since the voltage responses occur within seconds to minutes after irradiation, it is likely that an early consequence of the absorption of phototropically active light is to alter the properties of cell membranes. Since the primary site of auxin activity is also thought to be the cell membrane (3), it is perhaps logical that the interacting processes of photoreception and hormone-induced elongation are coordinated at the membrane level.…”