Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis II. Axial potential difference

Vital staining with pH indicator dyes made it possible to identifythe xylem with the specific channel A, reported previously,through which hydrogen ions flow generating a resting potentialdifference along the germ axis as their diffusion potential.The distribution of K+ concentration within this channel showedno similarity to electric potential distribution, in contrastto the distribution of H+. The axial P.D. between both ends of a segment cut from a hypocotylresponded reversibly to the change in O₂ tension of the surroundinggas phase. After air had been quickly replaced by N₂, a lagperiod appeared before the sudden potential drop took place.The lag period () was largely dependent on temperature. Apparentactivation energy of the process characterized by 1/ was 18Kcal/mole between 14–30?C, approximately equal to thatof the O₂-uptake within the same temperature range. The relationbetween O₂ concentration and the maximum rate of recovery ofP.D. from anoxia was of the Michaelis-Menten type; the apparentKm was calculated as 2.1 ? 10^–5M O₂ being of the sameorder as that of cytochrome oxidase in higher plants. The O₂-uptakerate "per unit of hypocotyl length" showed a distinct maximumin the elongating region where the axial distribution of bothelectric potential and pH within channel A had their minimums. (Received July 21, 1972; )     

Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis VI. The dual structure of radial electrogenic activity

The electrophysiological structure in bean hypocotyl was investigatedby the intracellular electrode method in combination with surfaceelectric potential (V_s) measurement and respiratory inhibitionby anoxia, with special reference to the membrane transportof ions and the formation of an absorption centre in the elongating(E) zone. The radial potential difference (V_sx: electric potentialdifference between the organ surface and a xylem vessel), onwhich axial distribution of V_a was dependent, comprised twocomponents; V_ax=V_px–V_ps. |V_px| (the potential differencebetween the inside of a parenchyma symplast and a xylem vessel)was at a maximum in the E-zone, while |V_ps| (the intracellularelectric potential with respect to the organ surface) was largestin the G-zone (mature zone), resulting in the characteristicdistribution pattern of V_s with a minimum in the E-zone. Therewere two independent electromotive forces which were both partiallydependent on respiration; one corresponding to V_ps located atthe surface of the parenchyma symplast (P) and the other toV_px located between P and the xylem (X). The electrogenic componentof Vpx was relatively small both in the hook (H) zone and theG-zone, but maximal in the E-zone of the hypocotyl. This resultwas consistent with the emergence of a maximum pH differencebetween P and X in the E-zone, where accumulation of K⁺ andwater were at a maximum, suggesting maximum activity of an H⁺-pumpextruding protons from P into X in exchange for K⁺. (Received July 17, 1978; )     

Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis IV. The effects of carbon monoxide and cyanide on the axial potential difference of hypocotyl segments

The effects of carbon monoxide and cyanide on the electric potentialdifference between both cut ends of a hypocotyl segment excisedfrom a bean embryo were investigated. Carbon monoxide definitely diminished the PD. This inhibitionwas photoreversible. The inhibition ratio was quantitativelyrelated to the [CO]/[O₂] ratio of the gas mixture. Prolongedexposure to a CO gas mixture induced spontaneous recovery ofthe PD, and this CO-resistant electrogenic activity was sensitiveto CN and also disappeared under anoxia. Cyanide also diminished the PD and often induced oscillationof the potential. The type of oscillation and the inhibitionratio varied with the concentration of CN. Sometimes CN pretreatmentcaused changes in the anoxia response of the potential. The time course of the spontaneous change in PD after cuttingof the hypocotylsegment also was investigated. (Received August 8, 1977; )     

Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis V. Electrogenic activity of the parenchyma cells in hypocotyl segments

Intracellular potential of parenchyma cells (V_ps) in the hypocotylsegment of Vigna sesquipedalis was initially low after excision,then gradually increased to a more negative level. ThereafterV_ps could be remarkably reduced under anoxia then recoveredwith reaeration, accompanied by several cycles of damped oscillations.Both the rapidity of the decrease of V_ps caused by anoxia andits temperature dependency suggest an electrogenic mechanism.No marked spatial differences along the germ axis and the radiusof hypocotyl were observed in the V_ps level and its electrogeniccomponent when the reference electrode was placed on the surfaceof the hypocotyl segment. V_ps also decreased rapidly in an atmospherecontaining 80% CO+20% O₂ in the dark, then was recovered immediatelyin the light or spontaneously but very slowly in the dark. Theextent of the decrease of V_ps caused by CO depended on the growthactivity of the cell and the time lapse after excision. Theseresults suggest the possible conversion or replacement of theterminal oxidase. Sometimes phenomena resembling those of actionpotentials occurred spontaneously or during the reduction ofV_ps due to inhibition of the energy metabolism. V_ps in the elongatingregion varied transiently with the change in illumination. Interrelationshipbetween V_ps and the surface resting potential is discussed. (Received July 20, 1977; )     

Automatic recording of electric potential and ion transport in frog skin

Summary An apparatus for the automatic recording of the bioelectric potential of isolated frog skin and of the short-circuit current, which is a measure of active Na⁺ transport, is described. The equivalence of the uninterrupted short-circuit current and active Na⁺ transport has been checked. Current and Na⁺ transport agreed within 2%.The automatic ion transport recorder is particularly suited in studies where the exact time course of the effects of enzyme inhibitors, drugs and other chemicals on skin is of interest. This is illustrated by showing the effects of fluoroacetate, quinone and hydroquinone on spontaneous skin potential and short-circuit current.Attention is called to characteristic transients in the potential records which are probably related to changes in skin permeability to passively moving chloride ions.Supported by Public Health Grant RG 3545.     

Effects of carbon dioxide on the spatially separate electrogenic ion pumps and the growth rate in the hypocotyl ofVigna sesquipedalis

Carbon dioxide, introduced into the gas phase of the experimental chamber, has distinct effects on two spatially separate membrane potentials and the rate of elongation growth in hypocotyl segments ofVigna sesquipedalis Wight. Both membrane potentials (V _ps andV _px=the electric potential difference between the parenchyma symplast and the surface of the hypocotyl, and that between the parenchyma symplast and the xylem, respectively) hyperpolarized rapidly but transiently at the introduction of CO₂. Prolonged exposure of the hypocotyl to high concentrations of CO₂ (above 10%) caused depolarization of membrane potentials above the level before CO₂ introduction. When CO₂ was replaced with air, the membrane potentials exhibited a distinct depolarization response of transient nature. The growth rate of the hypocotyl segments exhibited similar responses to CO₂ as did the membrane potentials (the increase and the decrease of the growth rate were corresponded to the hyperpolarization and the depolarization, respectively), but these responses always followed the changes of the membrane potentials. The CO₂-induced maximum hyperpolarization ofV _ps and the maximum increase of the growth rate were closely correlated. All these responses were strictly dependent on aerobic metabolism. These results indicate that CO₂ may regulate elongation growth in two ways: by affecting the activity of the electrogenic ion pump via intracellular acidification, and also by acting via apoplastic acidification as a wall-loosening acid.Symbols and abbreviations V _sx electric potential difference between the surface (S) and the xylem (X) of the hypocotyl - V _px electric potential difference between the inside of a parenchyma cell (P) andX - V _ps electric potential difference betweenP andS - V _ps (CO₂, max) the maximum value of CO₂-induced hyperpolarization ofV _ps - GR(CO₂, max) the maximum value of CO₂-induced increase of the growth rate - IAA indole-3-acetic acid     

Radial electrogenic activity in the stem of Vigna sesquipedalis: involvement of spatially separate pumps

Abstract. The surface electric potential of Vigna sesquipedalis stem, relative to that of the root medium, was most negative in the elongating zone where the difference in pH between parenchyma (P) and xylem sap (X) was at a maximum. The surface electrical potential was found to be determined by the distribution of radial potential difference ( V _sx comprised two components; V_sx= V _px− V _ps.There were two electromotive forces, generating V _ps at the surface of the parenchyma symplast and V _px between P and X; both were partially dependent on respiration. The depolarization of V _px upon removal of O₂ was maximal in the elongating zone, suggesting that the activity of an H⁺-pump extruding protons from the parenchyma into the xylem in exchange for K⁺ was greatest in this zone.     

Transmembrane electric potential difference in the protein-pigment complex of photosystem 2

The protein-pigment complex of photosystem 2 (PS2) localized in the thylakoid membranes of higher plants, algae, and cyanobacteria is the main source of oxygen on Earth. The light-induced functioning of PS2 is directly linked to electron and proton transfer across the membrane, which results in the formation of transmembrane electric potential difference (ΔΨ). The major contribution to ΔΨ of the PS2 reaction center is due to charge separation between the primary chlorophyll donor P₆₈₀ and the quinone acceptor Q_A, accompanied by re-reduction of P ₆₈₀ ⁺ by the redox-active tyrosine residue Y_Z. The processes associated with the uptake and release of protons on the acceptor and donor sides of the enzyme, respectively, are also coupled with ΔΨ generation. The objective of this work was to describe the mechanisms of ΔΨ generation associated with the S-state transitions of the water-oxidizing complex in intact PS2 complex and in PS2 preparation depleted of Mn₄Ca cluster in the presence of artificial electron donors. The findings elucidate the mechanisms of electrogenic reactions on the PS2 donor side and may be a basis for development of an effective solar energy conversion system.     

Effect of anomalous ion inertia and oblique ion viscosity on the radial electric field in FT-2 tokamak experiments

Results are presented from numerical simulations that show that, in a plasma with well-developed turbulence, the radial electric field can be positive in the region where the gradients of the plasma parameters are steep. In a plasma in which the turbulence is suppressed (as is the case with auxiliary lower hybrid heating), the radial electric field is found to exhibit a nearly neoclassical behavior during the formation of a transport barrier and transition to the H-mode.     

Tissue specificity of assimilation and transport of nitrogen in the root ofZea mays L. seedlings. III. Interaction of radial and longitudinal transport

Roots obtained from 4-day maize seedlings were allowed to absorb uniformly labelled¹⁴C-suorose only with their middle part while the apical and basal parts did not contact the medium. The amino acids and their amides produced in the cortex at the expense of nitrates and the¹⁴C-sucrose carbon moved radially to the stele where they were selectively distributed in the polar directions of transport. “Primary” amino acids moved predominantly in the apical direction while amides and basic amino acids were transported mainly in the opposite direction. When the nutrient medium was devoid of nitrogen sources, the amino acids entering the stele from the cortex were transported mostly to the root tip, indicating a significant role of young tissues in consuming organic nitrogen compounds when they are in short supply in the root.     

Distribution of glycoconjugates in ion transport cells of gerbil inner ear.

Ion transport cells in gerbil inner ear were differentiated histochemically by staining glycoconjugates (GCs) with a battery of horseradish peroxidase-conjugated lectins. Strong staining with PSA and LCA showed a high content of N-linked oligosaccharides in transport cell GCs. Reactivity with PHA-L and PHA-E identified GC with triantennary and with bisected biantennary N-linked oligosaccharides, respectively, in these cells. High affinity for DSA and PWM demonstrated abundant N-acetyl lactosamine in N-linked side chains. Ion transporting epithelial cells reacting with lectins specific for N-linked oligosaccharides included strial marginal cells and outer sulcus cells of the cochlea and dark cells, transitional cells, and planum semilunatum cells of the vestibular system. In general, all of the inner ear transport epithelial cells revealed a similar lectin binding profile, with the one exception that SBA reacted strongly with ion transporting cells in the vestibular system but only weakly with those in the cochlea. Fibrocytes specialized for ion transport located in distinct areas in the suprastrial and inferior regions of the spiral ligament also stained with lectins that demonstrate N-glycosylation. However, transport fibrocytes differed from transport epithelial cells in two ways. First, they reacted e with HPA, DBA, VVA, and SJA specific for O-linkages and second, they failed to react with UEA I. The staining pattern for N-glycosylated GC resembled that for Na+, K(+)-ATPase in inner ear, suggesting a relationship between these constituents.     

Acid-induced changes in the in vivo wall-yielding properties of hypocotyl sections of Vigna unguiculata

Elongation growth of hypocotyl sections of Vigna unguiculata under xylem perfusion was significantly enhanced when acid was applied by acid-aerosol to an abraded hypocotyl surface in the air. The in vivo wall extensibility (φ) and the effective turgor (Pⁱ– Y), both of which were determined by the pressure-jump method, increased during acid-induced growth as observed in IAA-induced growth. The intracellular pressure (Pⁱ), however, decreased significantly at the beginning of acid-induced growth whereas Pⁱ scarcely changed in IAA-induced growth. This result indicates that protons increase the effective turgor by decreasing the yield threshold as IAA does. There seems to be no essential difference between proton and auxin in the effects on the in vivo mechanical properties of the surface cell wall.     

Changes in the properties of cell wall pectin methylesterase along the Vigna radiata hypocotyl

The properties of cell wall pectinesterase (EC 3.1.1.11) from Vigna radiata (L.) Wilczek hypocotyl were investigated with immobilized and solubilized wall enzymes. Along the hypocotyl, the decrease of growth potential coincides with significant changes of the characteristics of the pectinesterase activities. As hypocotyl cells grow older, the proportion of ionically bound enzymes decreases and pH profile, sensitivity to cations and affinity for pectin change. The possible significance of these observations is discussed.     

Electrochemical potential difference for H+-ions as a regulator of redox profile of membrane during ATP-dependent ion transport in E. coli

The importance of delta mu H+ for transport of K+ via K(+)-ionophore and H(+)-K(+)-pump was studied. It was shown that the operation of the pump was decelerated by oxidant ferrycyanide, whereas sulfhydryl reagent dithiothreitol (DTT) drastically accelerated ATP driven ion exchange. Introduction of protonophore CCCP into the medium completely blocked the pump operation. However, the addition of DTT after CCCP restored the high level activity of the pump. At the same time DTT was unable to restore K+ accumulation after CCCP in aerobically grown bacteria for which the K+ uptake was performed across the electrical field gradient. Thus it was established that delta mu H+ was necessary for ATP driven ionic systems as a regulator of the membrane redox state.     

Electrochemical potential and ion transport in vesicles of yeast plasma membrane

Vesicles from yeast plasma membrane were prepared according to Franzusoff and Cirillo [1983) J. Biol. Chem. 258, 3608), with slight modifications. When Mg-ATP was added, this preparation was able to generate a membrane potential, that was sensitive to inhibitors of the yeast H+-ATPase and uncouplers, and could be decreased by the addition of permeant anions, as measured by the fluorescence changes of the dye oxonol V. The addition of ATP could also generate a pH gradient, detectable by the fluorescence changes of the monitor aminochloromethoxyacridine. This gradient was sensitive to inhibitors of ATPase and uncouplers, and could be increased by the addition of permeant anions to the incubation mixture. When the vesicles were loaded with KCl, an increased rate of K+ efflux was produced upon the addition of ATP. Cytochrome oxidase from bovine heart could be reconstituted into the vesicles and was shown to generate a membrane potential difference, negative inside, evidenced by the fluorescence quenching of the cyanide dipropylthiacarbocyanine and the uptake of tetraphenylphosphonium. Besides, in these vesicles, K+ and Rb+, but not Na+ or NH+4 could decrease the quenching of fluorescence and the uptake of tetraphenylphosphonium produced when the electron-donor system was present. In the vesicles in which cytochrome oxidase was incorporated, upon the addition of cytochrome c and ascorbate, the uptake of 86Rb+ could be demonstrated also. This uptake was found to be saturable and inhibited by K+, and to a lesser degree by Na+. The results obtained indicate that these vesicles are reasonably sealed and capable of generating and maintaining a membrane potential. The membrane potential could be used to drive ions across the membrane of the vesicles, indicating the presence and functionality of the monovalent cation carrier. The vesicles, in general terms seem to be suitable for studying transport of ions and metabolites in yeast.