Influence of Phenolic Acids on Ion Uptake

Abstract

The membrane potentials of aged, excised barley (Hordeum vulgare L.) root cells were rapidly depolarized by the addition of salicylic acid (o-hydroxybenzoic acid) The phenomenon of allelopathy, in which one species of plant may dramatically inhibit the development of others by producing and releasing specific compounds into the environment, is well documented (18). In a few cases, the allelopathic compounds and their mode of transmission have been elucidated (11,12). In a large number of reported cases, however, the modes of action of the allelopathic compounds (allelochemicals) are not understood. This paper reports further investigations into the mode of action of an important group of allelochemicals, phenolic acids.Earlier papers by Glass (3)(4)(5) have established that one ubiquitous group of phenolics, namely benzoic and cinnamic acids, are potent inhibitors of active K and Pi absorption by excised barley roots. The effect is readily reversible and the inhibitory capacity of the benzoic acids is strongly correlated with their lipid solubilities. From these results it was suggested that phenolics act directly on the cell membrane, modifying its permeability and thereby increasing the rate of efflux of ions. To test this hypothesis the effect of phenolics on cell membrane electrical potentials has been studied. According to the Goldman (7) where E is the electropotential difference (PD) between o, the outer solution and i, the inner solution; R, the gas constant (joules degree mole); T, the absolute temperature; F, the Faraday (coulombs equivalent-'); P subscript is the permeability coefficient of a univalent cation, j+, or a univalent anion, j-; C,+°, the concentration of j+ outside, and Cj,+, the concentration of j+ inside. Predictions of E based only upon K+ and Clcharacteristics, derived from the above equation, may under certain conditions be remarkably consistent with measured values for root cell membrane potentials (14). Clearly any alterations of the permeability properties of the cell membrane with regard to K+ or Cl-will be reflected by changes in E. If the cell membrane became extremely permeable, the imbalance of ion concentration across the cell membrane, which is necessary for E, would disappear and E would fall to near zero. MATERIALS AND METHODSSeedlings of Hordeum vulgare L. cv. Karlsberg were grown for 3 or 4 days in aerated 5 X 10-' M CaSO, solution following a 1-day germination in aerated distilled water. At the end of this period, the last 1 to 1.5 cm of roots were excised from the root tip and allowed to age in aerated 5 X 10-M CaSO4 solution. It was found that the aging process produced a very significant increase in the cell membrane potential of the order reported by Pitman et al. (14). Membrane potentials of cells in the root tips were measured with microcapillary electrodes using the apparatus described by Dunlop and Bowling (2). During determinations of membrane potentials the root tips were held in a 5 ml Plexiglas chamber which, under control conditions, contained a ...

Aspects of Rainforest Regeneration

“…Glass (1973Glass ( , 1974 demonstrated that in short-term experiments, uptake of K and phosphate was inhibited by phenolic compounds which strongly infiuenced cell membrane potentials. Glass and Dunlop (1974) support the hypothesis that phenolic infiuence on ion uptake is mediated through direct non-specific effects upon cell membrane permeability. Stowe and Osborn (1980) also reported an interaction between phenolics and nutrients; phytotoxicity of coumaric and vanillic acids increased at low nutrient levels.…”

Boron, Lignification and the Origin of Vascular Plants‐a Unified Hypothesis

“…They argued that the effects of boron deficiency were direct and not mediated by accumulation of phenolic compounds since ' a reversibly impaired ATP-ase has been isolated from boron-deficient plants under conditions which should remove any phenolics bound to the membrane' (my italics). However, exogenous phenolics can markedly inhibit uptake of both anions and cations by roots of barley and soy-bean (Glass, 1973(Glass, , 1974Glass and Dunlop, 1974;McClure, Gross and Jackson, 1978). It remains to be seen how increased levels of endogenous phenols, brought about by boron deficiency (see pp.…”

In vitroallelopathic potential ofLeonurus sibiricusL. leaves

“…Flavonoids with this structural arrangement are reported to alter the permeability of the cellular membranes and to affect the radicular lengthening necessary for the root protrusion (Glass and Dunlop 1974;Martı´nez-Flo´rez et al 2002;Einhellig 2004). On the other hand, the presence of sugar moieties in the flavonoids seems to be uninfluent: in fact, both isoquercetrin and rutin showed inhibitory activity against lettuce germination, whereas hyperin and quercetin-3-O-a-L-rhamnopyranosyl-(1 6)-b-D-galactopyranoside do not significantly affect the germination.…”