Adenine-nucleotide levels and metabolism-dependent membrane potential in cells of Nitellopsis obtusa Groves

The relationship between adenine-nucleotide levels and metabolism-dependent membrane potential was studied in cells of Nitellopsis obtusa. Effects of ADP and AMP in the presence of ATP on electrogenic pump activity were measured in the dark, using the continuous perfusion method. Both ADP and AMP acte as competitive inhibitors for ATP, the K_i value for either compound being about 0.4 mM. The role of ADP and AMP as regulating factors for the electrogenic pump was investigated under various metabolic conditions. Application of N₂ gas in the dark caused a significant membrane depolarization amounting to 90 mV, but cytoplasmic streaming and membrane excitability were not affected. Under anoxia, the ATP level decreased from 1.6 to 0.5 mM; ADP increased but only slightly, and AMP increased greatly. However, the time course of changes in the adenine nucleotides was not concurrent with that of the membrane-potential changes, thus, the adenine-nucleotide level changes cannot fully account for the N₂-elicited depolarization. Under light, although the membrane hyperpolarized, no significant changes in the adenine-nucleotide levels were observed. Therefore, the light-induced membrane hyperpolarization cannot be explained solely by changes in adenine-nucleotide levels.Abbreviations APW artificial pond water - E_m membrane potential - R_m membrane resistance     

Heavy metal resistance patterns of Frankia strains

The sensitivity of 12 Frankia strains to heavy metals was determined by a growth inhibition assay. In general, all of the strains were sensitive to low concentrations (<0.5 mM) of Ag(1+), AsO(2)(1-), Cd(2+), SbO(2)(1-), and Ni(2+), but most of the strains were less sensitive to Pb(2+) (6 to 8 mM), CrO(4)(2-) (1.0 to 1.75 mM), AsO(4)(3-) (>50 mM), and SeO(2)(2-) (1.5 to 3.5 mM). While most strains were sensitive to 0.1 mM Cu(2+), four strains were resistant to elevated levels of Cu(2+) (2 to 5 mM and concentrations as high as 20 mM). The mechanism of SeO(2)(2-) resistance seems to involve reduction of the selenite oxyanion to insoluble elemental selenium, whereas Pb(2+) resistance and Cu(2+) resistance may involve sequestration or binding mechanisms. Indications of the resistance mechanisms for the other heavy metals were not as clear.     

Bioelectrical reactions of Nitellopsis obtusa induced by indole-3-acetic acid

The complex of bioelectrical paramenters (membrane potential, membrane resistance and capacitance) of internodal cells of Nitellopsis obtusa was measured over a wide range of IAA concentration (10⁻¹⁰ to 10⁻⁴ M ) with two intracellular microelectrodes. Primary effects of IAA at a concentration as low as 10⁻¹⁰ M were observed. The optimum range of IAA action was from 10⁻⁹ to 10⁻⁶ M . The type of IAA-induced electroresponse depended on the initial level of membrane potential, which characterized the energetic state of the plasmalemma. In the energized state (ca −200 mV) N. obtusa cells appeared to have 3 typical reactions: hyperpolarization (membrane potential less than K⁺-equilibrium potential), depolarization (membrane potential higher than K⁺-potential) and absence of response at K⁺-electrochemical equilibrium. Membrane capacitance was found constant at 0.74 ± 0.05 μF cm⁻², but membrane resistance increased up to 50% independently of the sign of the electrogenic reaction. Increase of membrance capacitance and decrease of the membrane resistance was a feature of the de-energized state (ca −135 mV) and may be explained by lower viscosity of membrane lipids, which interacted with IAA. The complex of parameter, including cytoplasmic steaming taken as an indicator of energy supply, is discussed as indicating slow IAA penetration combined with a primary action of IAA on the plasmalemma receptor sites.     

Effect of cadmium on growth, proton extrusion and membrane potential in maize coleoptile segments

Cd accumulation, its effects on elongation growth of maize coleoptile segments, pH changes of their incubation medium and the membrane potential of parenchymal cells were studied. The Cd content increased significantly with exposure to increasing cadmium concentrations. Coleoptile segments accumulated the metal more efficiently in the range 10–100 μM Cd, than in the range 100–1000 μM Cd. Cd at concentrations higher than 1.0 μM produced a significant inhibition of both growth and proton extrusion. 100 μM Cd caused depolarization of the plasma membrane (PM) potential in parenchymal cells. The simultaneous treatment of maize coleoptile segments by indole-3-acetic acid (IAA) and Cd, counteracted the toxic effect of Cd on growth. Moreover, our data also showed that 100 μM Cd suppressed the characteristic IAA-induced hyperpolarization of the membrane potential, causing membrane depolarization. These results indicate that the toxic effect of Cd on growth of maize coleoptile segments might be, at least in part, caused via reduced PM H⁺-ATPase activity.     

Changes in the neuronal membrane potential of the mollusk Planorbarius corneus under the action of cardiac glycosides

In experiments on isolated neurones from the gastropod mollusc P. corneus, strophantin and digoxin in low concentrations produce slow hyperpolarization, in higher ones--depolarization; at concentrations about 1 mM, hyperpolarization was more evident. In all cases, the decrease in membrane resistance was observed. Presumably, membrane permeability for potassium ions increases. During application of the drugs in concentrations 10-100 microM, hyperpolarization may be masked by depolarization due to block of Na,K-pump. Higher concentrations, increasing potassium permeability of the membrane, may result in substitution of depolarization by hyperpolarization.     

TheBulla ocular circadian pacemaker

In an effort to understand the cellular basis of entrainment of circadian oscillators we have studied the role of membrane potential changes in the neurons which comprise the ocular circadian pacemaker of Bulla gouldiana in mediating phase shifts of the ocular circadian rhythm. We report that: 1. Intracellular recording was used to measure directly the effects of the phase shifting agents light, serotonin, and 8-bromo-cAMP on the membrane potential of the basal retinal neurons. We found that light pulses evoke a transient depolarization followed by a smaller sustained depolarization. Application of serotonin produced a biphasic response; a transient depolarization followed by a sustained hyperpolarization. Application of a membrane permeable analog of the intracellular second messenger cAMP, 8-bromo-cAMP, elicited sustained hyperpolarization, and occasionally a weak phasic depolarization. 2. Changing the membrane potential of the basal retinal neurons directly and selectively with intracellularly injected current phase shifts the ocular circadian rhythm. Both depolarizing and hyperpolarizing current can shift the phase of the circadian oscillator. Depolarizing current mimics the phase shifting action of light, while hyperpolarizing current produces phase shifts which are transposed approximately 180 degrees in circadian time to depolarization. 3. Altering BRN membrane potential with ionic treatments, depolarizing with elevated K+ seawater or hyperpolarizing with lowered Na+ seawater, produces phase shifts similar to current injection. 4. The light-induced depolarization of the basal retinal neurons is necessary for phase shifts by light. Suppressing the light-induced depolarization with injected current inhibits light-induced phase shifts. 5. The ability of membrane potential changes to shift oscillator phase is dependent on extracellular calcium. Reducing extracellular free Ca++ from 10 mM to 1.3 X 10(-7) M inhibits light-induced phase shifts without blocking the photic response of the BRNs. The results indicate that changes in the membrane potential of the pacemaker neurons play a critical role in phase shifting the circadian rhythm, and imply that a voltage-dependent and calcium-dependent process, possibly Ca++ influx, shifts oscillator phase in response to light.     

Effects of cadmium and lead on ferric chelate reductase activities in sugar beet roots

The effects of the heavy metals Cd and Pb on the activity of the enzyme ferric chelate reductase (FC-R, E.C. 1.6.99.13) have been studied in excised sugar beet root tips. The activity of this enzyme is markedly increased by iron deficiency. Metals were used as chloride salts or chelated with EDTA, and chemical speciation was carried out to predict the metal chemical species in equilibrium both in the ferric reductase assay and in the nutrient solutions. Three different heavy metal treatments were used. First, effects of Cd and Pb on the functioning of the FC-R were assessed in Fe-deficient plants, by including metals in the enzyme assay medium only. Results indicate that 50 μM CdCl₂ or Cd-EDTA did not affect FC-R activities even when assay time was as long as 2 h, whereas Pb slightly decreased enzyme activity only at concentrations of 2 mM. Second, short-time Cd and Pb pre-treatments (30–60 min) were imposed on intact Fe-deficient plants before carrying out the assay of FC-R activity. These short-term treatments induced significant decreases in the FC-R activities previously induced by Fe deficiency. With Cd, effects were more pronounced at higher concentrations, and they were stronger when Cd was in the free ion form than when present in the form of Cd-EDTA chelate. Third, prolonged Cd and Pb treatments were imposed on plants grown on 45 μM Fe-EDTA to assess the long-term effects of heavy metals on the induction of the FC-R enzyme. These long-term heavy metal treatments caused a significant increase in the root FC-R activities, indicating that Cd and Pb induce a deficiency in Fe in sugar beet that in turn elicits FC-R activity. The increases, however, are not as large as those found in total absence of Fe.     

Effects of membrane potential on calcium fluxes of Pelvetia eggs

⁴⁵Ca²⁺ fluxes across the plasma membrane of zygotes of the fucoid alga, Pelvetia fastagiata (J. Ag.) De Toni, were studied in artificial sea waters of various potassium concentrations. Except for two cases, hyperpolarization of the cell membrane (with low [K⁺]) increases, and depolarization (with high [K⁺]) decreases the influx of Ca²⁺ over the range of [K⁺] studied (1–100 mM). The fractional increases of influx during hyperpolarization are close to the fractional increases in membrane potential but the decreases during depolarization are much smaller than those in membrane potential. In two anomalous cases, the influxes of ⁴⁵Ca²⁺ at a potassium concentration of 30 mM were about 20% higher than the control value instead of being 10% lower.The effluxes of ⁴⁵Ca²⁺ are increased by both hyperpolarization and by depolarization. On balance (and excepting the two anomalous cases) the net result of hyperpolarization should be to increase and that of depolarization to decrease intracellular [Ca²⁺].     

Accumulation of Cd and Pb in various body parts,organs and tissues of Lymantria dispar asiatica (Lepidoptera: Erebidae)

To investigate the accumulation patterns of Cd and/or Pb in various body parts, organs and tissues of the Asian gypsy moth (Lymantria dispar) larvae under Cd and/or Pb stress, Cd and Pb treated artificial diets were used to feed the larvae in the current study. These larval body parts/organs/tissues included the heads, integuments (body walls), alimentary canals, fat bodies and hemolymphs. Our results showed that under Cd and/or Pb stress, their accumulations in larval body parts/organs/tissues were significantly higher than those in the control, with the amounts of tested metals in the fat bodies and hemolymphs and alimentary canals being significantly higher than those in the heads and integuments. Under the single Cd (0, 7.5, 10.5 mg/kg) or Pb stress (0, 55, 90, 125 mg/kg), the accumulations of these heavy metals were positively correlated with their concentrations in diets. Under the combined stress (Cd × Pb), the Cd accumulation at the lower Pb concentrations was higher than that at higher Pb concentrations for the body parts/organs/tissues, similar effects of Cd concentrations on Pb accumulations were also recorded. These results clearly showed that Cd and/or Pb were accumulated in various body parts/organs/tissues at different levels under the heavy metal stress. And accumulations of Pb/Cd were positively correlated with their concentrations in the diets under the single stress. Under the combined stresses, Cd and Pb had synergistic effects at low concentrations whereas antagonistic effects at high concentrations. The accumulations of Cd and/or Pb in the gypsy moth larvae affects normal physiological and biochemical functions, and thus affects their growth and development.     

Vesicle release from rat red cell ghosts and increased association of cell membrane proteins with cytoskeletons induced by cadmium

When rat red cell ghosts were incubated with 0.1-0.5 mM CdCl2 in 10 mM Tris-HCl (pH 7.4) at 37 degrees C for 30 min, they became irregular in shape and released small vesicles. The release of vesicles was dependent on the incubation temperature and Cd2+ concentration. The maximum release occurred at 37 degrees C in the presence of 0.2 mM Cd2+. The protein composition of Cd2+-induced vesicles was similar to that of the vesicles released from ATP-depleted red cells. Upon incubation with 0.1-0.2 mM Cd2+, more than 90% of the Cd2+ added to the incubation buffer was recovered in ghosts and 15-20% of the ghost Cd2+ was located on the cytoskeletons prepared by washing ghosts with 0.5% Triton X-100 solution containing 0.1 M KCl and 10 mM Tris-HCl (pH 7.4). Moreover, the cytoskeletons prepared from Cd2+-treated ghosts markedly contained cell membrane proteins, bands 2.1, 3, 4.2 and 4.5, and glycophorins. The association of bands 3 and 4.2 with cytoskeletons increased with increasing concentrations of Cd2+ added to the incubation buffer and saturated at 0.2 mM Cd2+. The solubilization of cytoskeletal proteins, bands 1, 2 and 5, from ghosts at low ionic strength was almost completely suppressed by preincubation of ghosts with 0.1 mM Cd2+. HgCl2, PbCl2 and ZnCl2 at 0.2 mM each also produced an increased association of cell membrane proteins with cytoskeletons, whereas CaCl2 and MgCl2 did not.     

Effect of heavy metals on the growth of tropical microalga Tetrasermis chuii (Prasinophyceae)

We determined the toxic effect of four metals, cadmium (Cd), copper (Cu), mercury (Hg) and lead (Pb), on the tropical microalga Tetraselmis Chuii (Butcher, 1959). We exposed 50 ml of cultivated microalgae (f/2 Guillard) in the exponential growth phase, with three replicates, to concentrations of 0 (control). 0.1, 1.0, 5.0, 10.0 and 20.0 mgxl(-1) with each metal for 96 hr. We evaluated the lethal effect daily, through the cellular count. In the control treatment (not exposed to any metal) we observed an increase in cellular density. In all treatments exposed to metals, we observed a decrease in cellular density, which accelerated in 48 h, after which it became less pronounced. There were exceptions with low concentrations of Cd and Cu at 24 h, as there was no significant decrease, probably due to their use as micronutrients at these low concentrations. The metal that caused the most lethal effect was Pb, which killed 50% of the microalgal population at a concentration of 0.40 mg x l(-1). This concentration was 3 times lower than that of mercury and 13 times lower than those of cadmium and copper. The microalga Tetraselmis chuii is recommended as a model species to estimate the toxic effects of xenobiotics on tropical seawater environments.     

珠江三角洲马尾松年轮重金属含量年代变化

采用树木年轮化学分析手段,探讨了肇庆鼎湖山(相对清洁区)和南海西樵山(污染区)马尾松(Pinus massonianaL.)不同时期木质部6种重金属(Cu、Zn、Ni、Cd、Cr和Pb)含量的年代变化。结果表明:西樵山马尾松林地表层土壤Cu、Zn、Cd和Pb含量均超过其在广东省表层土壤环境背景值,鼎湖山马尾松林地表层土壤除Cd外其余重金属含量在背景值范围内;鼎湖山和西樵山马尾松木质部中Cu、Zn、Cr和Pb含量均呈现从心材到边材上升的分布格局,反映了珠江三角洲环境中可供植物利用的重金属在过去有了增加。Cu、Zn、Ni,特别是Cr和Pb的最大含量出现在1990年后形成的木质部中,两地环境(土壤和大气)中重金属含量增加是导致马尾松木质部重金属含量上升的主要原因;在相同时期形成的木质部中,西樵山马尾松木质部Cu、Cr和Pb的含量大于鼎湖山,Zn、Ni和Cd含量则小于鼎湖山,这与环境重金属含量差异有关,也与马尾松对不同重金属的富集能力有关。马尾松年轮化学分析的结果能够提供珠三角地区重金属的历史变化信息。     

Effect of acute hypoxia on glomus cell Em and psi m as measured by fluorescence imaging.

We have reinvestigated the hypothesis of the relative importance of glomus cell plasma and mitochondrial membrane potentials (E(m) and psi(m), respectively) in acute hypoxia by a noninvasive fluorescence microimaging technique using the voltage-sensitive dyes bis-oxonol and JC-1, respectively. Short-term (24 h)-cultured rat glomus cells and cultured PC-12 cells were used for the study. Glomus cell E(m) depolarization was indirectly confirmed by an increase in bis-oxonol (an anionic probe) fluorescence due to a graded increase in extracellular K(+). Fluorescence responses of glomus cell E(m) to acute hypoxia (approximately 10 Torr Po(2)) indicated depolarization in 20%, no response in 45%, and hyperpolarization in 35% of the cells tested, whereas all PC-12 cells consistently depolarized in response to hypoxia. Furthermore, glomus cell E(m) hyperpolarization was confirmed with high CO (approximately 500 Torr). Glomus cell psi(m) depolarization was indirectly assessed by a decrease in JC-1 (a cationic probe) fluorescence. Accordingly, 1 microM carbonyl cyanide p-trifluoromethoxyphenylhydrazone (an uncoupler of oxidative phosphorylation), high CO (a metabolic inhibitor), and acute hypoxia (approximately 10 Torr Po(2)) consistently depolarized the mitochondria in all glomus cells tested. Likewise, all PC-12 cell mitochondria depolarized in response to FCCP and hypoxia. Thus, although bis-oxonol could not show glomus cell depolarization consistently, JC-1 monitored glomus cell mitochondrial depolarization as an inevitable phenomenon in hypoxia. Overall, these responses supported our "metabomembrane hypothesis" of chemoreception.     

Comparison of antioxidant responses to cadmium and lead in Bruguiera gymnorrhiza seedlings

Seedlings of mangrove plant Bruguiera gymnorrhiza cultured in sand with Hoagland’s nutrient solution were treated with 1 to 30 mM Cd(NO₃)₂ or Pb(NO₃)₂ for 2 months. In all Cd/Pb treatments, the malondialdehyde content increased while the chlorophyll content declined. Peroxidase (POD) and superoxide dismutase (SOD) activities in roots increased at moderate Cd/Pb concentrations (1–10 mM), whereas decreased at higher concentrations (20–30 mM). Catalase (CAT) activity in roots was inhibited by 1–10 mM Cd but enhanced by 1–10 mM Pb. The activities of POD, SOD and CAT in leaves were less affected by Cd and Pb than in roots. A new SOD and three CAT isoenzymes were induced by Pb. In contrast, no additional SOD and CAT isoenzymes were induced by Cd.     

Photosynthetic control of the plasma membrane H+-ATPase in Vallisneria leaves. I. Regulation of activity during light-induced membrane hyperpolarization

In mesophyll cells of the aquatic angiosperm Vallisneria gigantea Graebner, red, blue, or blue plus far-red light induced a typical membrane hyperpolarization, whereas far-red light alone had little effect. Both N,N'-dicyclohexylcarbodiimide, a potent inhibitor of H+-ATPase, and carbonylcyanide m-chlorophenylhydrazone, an uncoupler, produced a considerable membrane depolarization in the dark-adapted cells and a complete suppression of the light-induced hyperpolarization. Although 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, did not affect the membrane potential in darkness, it completely inhibited the light-induced membrane hyperpolarization. In vivo illumination of the leaves with red light caused a substantial decrease in the Km for ATP, not only of the vanadate-sensitive ATP-hydrolyzing activity in leaf homogenate, but also of the ATP-dependent H+-transporting activity in plasma membrane (PM) vesicles isolated from the leaves by aqueous polymer two-phase partitioning methods. The effects of red light were negated by the presence of DCMU during illumination. In vivo illumination with far-red light had no effect on the Km for ATP of H+-transporting activity. These results strongly suggest that an electrogenic component in the membrane potential of the mesophyll cell is generated by the PM H+-ATPase, and that photosynthesis-dependent modulation of the enzymatic activity of the PM H+-ATPase is involved in the light-induced membrane hyperpolarization.     

The interrelationship of cesium, intracellular sodium activity, and pacemaker potential in cardiac Purkinje fibers

The actions of cesium (Cs) on intracellular sodium activity (aiNa), membrane potentials, and force were studied in sheep cardiac Purkinje and myocardial fibers superfused in vitro. In Purkinje fibers, Cs (2 mM) decreased diastolic depolarization, aiNa (-6.7%, p less than 0.005), and force (-28.0%, p less than 0.01). The effects of 4 and 8 mM Cs were more pronounced. In quiescent fibers, Cs (2-4 mM) also decreased aiNa (-17.3%, p less than 0.005) and induced an initial hyperpolarization (+5.6 +/- 1.3%, p less than 0.005) followed by a return toward control. Diastolic depolarization was almost abolished by driving the fibers at 180/min (diastole was very short) but still Cs decreased aiNa (-15.4%). Tetrodotoxin decreased aiNa (-16.2%, p less than 0.025) and reduced the Cs-induced fall in aiNa (-2.2%, p less than 0.05). In zero [K]o, Cs decreased aiNa and caused repolarization. In 0.1 mM strophanthidin, Cs did not decrease aiNa any longer and affected the membrane potential little. In quiescent myocardial fibers, Cs (4 mM) decreased aiNa (-12.6%, p less than 0.05) and transiently hyperpolarized (+2.1%). Rubidium (2 mM) decreased aiNa and resting potential in Purkinje fibers and in myocardial fibers and also decreased diastolic depolarization in Purkinje fibers. Thus, cesium and rubidium decrease aiNa and modify the membrane potential but not through a block of the inward pacemaker current If.     

Effect of salicylic acid on nodulation, nitrogenous compounds and related enzymes of Vigna mungo

Plants of Vigna mungo raised from seeds presoaked in salicylic acid (0.0, 0.01, 0.1 and 1.0 mM) and nodulated with the cowpea strain of Rhizobium leguminosarum were analysed 15 and 30 d after sowing. The foliar nitrate and nitrite contents were varying but soluble protein and total nitrogen contents were lower in treated than control plants. Nitrate reductase activity was increased at the two lower concentrations of 0.01 and 0.1 mM but was inhibited at the highest concentration used (1.0 mM). The number of nodules, their leghemoglobin and protein contents and nitrogenase activity of roots were reduced. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal accumulation of metals by red alga Gracilaria verrucosa (Huds.) Papens. from Thermaikos Gulf, Greece

Concentrations of Fe, Pb, Cu, Zn and Cd were determined during one season in the red alga Gracilaria verrucosa, sediment and seawater from the Thermaikos Gulf, Greece. This region has been subject to change due to increases in industrial and domestic activities. The relative abundance of metals in G. verrucosa and seawater decreased in the order: Fe>Zn>Pb>Cu>Cd and in the sediment: Pb>Fe>Zn>Cu>Cd. Cadmium concentration in the alga correlated positively with that in seawater. There was positive correlation between Fe concentrations in the alga and those of the Zn and Cu. The concentrations of metals in the alga showed no significant differences between the stations. Lead, Zn and Cu concentrations in the alga were slightly higher at Biamyl, whereas Cd was higher at Perea and Fe at Nea Krini. Seasonal variation of metal concentrations in the alga was significant for Cd and Fe. Copper and Fe increased from winter to summer, whereas Cd was the opposite. Zinc concentrations were minimum and Pb concentrations were maximum during spring. These variations are discussed in relation to tissue age, life cycle, ambient concentrations of metals and other environmental conditions. Cd and Pb concentrations inG. verrucosa in the Thermaikos Gulf were higher and those of Cu and Zn were lower than in other species of the genus. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ion transport in Nitellopsis obtusa

The distribution and rates of exchange of the ions sodium, potassium, and chloride in single internodal cells of the ecorticate characean, Nitellopsis obtusa, have been studied. In tracer experiments three kinetic compartments were found, the outermost "free space" of the cell, a compartment we have called "protoplasmic non-free space", and the cell sap. The concentrations in the vacuole were 54 mM Na(+), 113 mM K(+), and 206 mM Cl(-). The steady state fluxes across the vacuolar membrane were 0.4 pmole Na(+)/cm.(2) sec., 0.25 pmole K(+)/cm.(2) sec., and 0.5 pmole Cl(-)/cm.(2) sec. The protoplasmic Na/K ratio is equal to that in the vacuole but protoplasmic chloride is relatively much lower. Osmotic considerations suggest a layer 4 to 6 micro thick with sodium and potassium concentrations close to those in the vacuole. The fluxes between protoplasm and external solution were of the order of 8 pmoles Na(+)/cm.(2) sec. and 4 pmoles K(+)/cm.(2) sec. We suggest that the protoplasm is separated from the cell wall by an outer protoplasmic membrane at which an outward sodium transport maintains the high K/Na ratio of the cell interior, and from the vacuole by the tonoplast at which an inward chloride transport maintains the high vacuolar chloride. The tonoplast appears to be the site of the principal diffusion resistance of the cell, but the outer protoplasmic membrane probably of the main part of the potential.     

Effect of Mentha x piperita essential oil and monoterpenes on cucumber root membrane potential.

Peppermint (Mentha piperita L.) essential oil and its main components were assessed for their ability to interfere with plant plasma membrane potentials. Tests were conducted on root segments isolated from etiolated seedlings of cucumber (Cucumis sativus L.). Increasing the concentration of peppermint essential oil from 5 to 50 ppm caused a decrease in membrane potential (Vm) hyperpolarization of 10-3 mV, whereas concentrations from 100 up to 900 ppm caused an increasing depolarization of Vm (from 5 to 110 mV). When tested at 300 ppm, (+)-menthyl acetate, (-)-limonene and 1,8-cineole did not exert any significant effect on V(m), whereas (+)-menthofuran (73 mV), (+)-pulegone (85 mV), (+)-neomenthol (96 mV), (-)-menthol (105 mV) and (-)-menthone (111 mV) showed increased ability to depolarize V(m). A plot of log of octanol-water partition coefficient (K(ow)) against their depolarizing effect showed a significant negative correlation, suggesting that among all monoterpenoids increased membrane depolarization depends on lower K(ow). However, among monoterpene ketones, alcohols and furans, increased membrane depolarization is associated with a decline in water solubility. The possible effect of monoterpenoids on membrane ion fluxes is also discussed, since changes in the bioelectric potential of cells imply changes in the flux of ions across the plasma membrane