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; )     

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 III. Significance of the radial potential difference

The distribution pattern of the trans-root surface potentialalong the germ axis of Vigna sesquipedalis intimately dependedon the existence of oxygen as well as the potential difference(PD) between both cut ends of a cylindrical segment of the hypocotyl.In the grown-up region (basal region) of the hypocotyl, a largechange of the trans-root surface potential occurred with anoxia,but not in the elongating zone except in the transient phaseafter reaeration. The distribution pattern of the trans-root stump potential alongthe germ axis, measured just after die hypocotyl had been cutat various positions, was nearly flat. However, PD between diecut stump and a point on the hypocotyl surface at sufficientdistance from the stump had a large value. The results are not explainable based on the axial electromotiveforces alone. Consideration of equivalent circuits of the hypocotylhas led to die idea that radial electromotive forces largelycontribute to generation of die distribution pattern of thesurface electric potential. (Received June 30, 1977; )     

Depolarization of transmembrane potential of corn and wheat coleoptiles under reduced water potential and after IAA application

The influence of IAA and temporarily reduced water potentialon the transmembrane potential (PD) of corn and wheat coleoptilesections was investigated. The studies were performed by twodifferent methods: discontinuous PD measurements with microelectrodesin corn coleoptile sections and continuous measurements withmicroelectrodes in wheat coleoptile sections. Both methods showeda very rapid depolarization of PD within a period of 2 to 5min. In corn coleoptile sections, a PD oscillation was observedwithin an average period of 14.5 min after IAA application andof 14.0 min after reduction of water potential. The PD amplitudewas about 20 to 25 mV. In wheat coleoptile sections, an oscillationof PD could not be definitely established. After an IAA-induceddepolarization period of 4 to 7 min, the initial potential sometimeswas restored, while in some other cases, a subsequent hyperpolarizationwas found although in most cases the depolarization continued.The discussion covers the possibility that a decrease in PDcaused by IAA and water stress may induce activation of H⁺ secretionby a plasmalemma H₊ pump. (Received November 24, 1978; )     

Spontaneous recovery of the anoxic diminution in the action potential plateau of the late embryonic and neonatal chicken hearts

The action potential plateau of the embryonic chick hearts at the latest stage of development (19- to 20-day-old) was depressed initially by anoxia but recovered spontaneously under the sustained anoxic condition. A similar spontaneous recovery of the action potential plateau was observed in hearts from neonatal chicks. Propranolol (3 × 10^?6M) did not affect the spontaneous recovery of the action potential plateau, excluding the possible involvement of the release of endogenous catecholamines. Since tissue adenosine triphosphate content continued to decrease during anoxia in these hearts, it is unlikely that the anoxia-resistant metabolic pathway appeared or was enhanced to supply the energy for the rebuilding of the plateau. In a Ca²⁺-free solution the action potential plateau rapidly disappeared and did not recover spontaneously during anoxia; at this time, however, the addition of Ca²⁺ (2 mM) prolonged the plateau. An inward calcium current may play an important role in spontaneous recovery of the action potential plateau during anoxia. The duration of the action potential decreased after hatching. From these results it is suggested that the mechanism underlying the action potential plateau may somehow differ in the hearts at the stages around the time of hatching.     

Effects of anoxia and high CO2 concentration on the electrogenic activity of leaf cell membrane in the dark

Resting membrane potential of a single cell in Antirrhinum leafdepolarized rapidly by about 40% under anoxia in the dark andrecovered to the normal level with reaeration. V_m in the dark comprised two fractions; one was passive diffusionpotential and the other was intimately dependent on aerobicmetabolism. The rapidity of the depolarization due to anoxiasuggested the possible functioning of an electrogenic mechanism,although the level of V_m was not much higher than the equilibriumpotential of K⁺ across membrane. 50% CO₂ in air brought about slightly more complex responses:a slight transient hyperpolarization and a subsequent depolarization.Sometimes one more transient depolarization took place as a"CO₂-off" effect. The total depolarization span was equal tothat caused by anoxia. 50% CO₂ under anoxia did not evoke furtherdepolarization but only hyperpolarization. (Received July 7, 1976; )     

Carbon monoxide affects electrical and contractile activity of rat myocardium

Background

Carbon monoxide (CO) is a toxic gas, which also acts in the organism as a neurotransmitter. It is generated as a by-product of heme breakdown catalyzed by heme oxygenase. We have investigated changes in electrical and contractile activity of isolated rat atrial and ventricular myocardium preparations under the influence of CO.

Methods

Standard microelectrode technique was used for intracellular registration of electrical activity in isolated preparations of atrial and ventricular myocardium. Contractions of atrial myocardial stripes were registered via force transducer.

Results

CO (10^-4 - 10^-3 M) caused prominent decrease of action potential duration (APD) in working atrial myocardium as well as significant acceleration of sinus rhythm. In addition CO reduced force of contractions and other parameters of contractile activity. Inhibitor of heme oxygenase zinc protoporphyrin IX exerts opposite effects: prolongation of action potential, reduction of sinus rhythm rate and enhancement of contractile function. Therefore, endogenous CO, which may be generated in the heart due to the presence of active heme oxygenase, is likely to exert the same effects as exogenous CO applied to the perfusing medium. In ventricular myocardium preparations exogenous CO also induced shortening of action potential, while zinc protoporphyrin IX produced the opposite effect.

Conclusions

Thus, endogenous or exogenous carbon monoxide may act as an important regulator of electrical and contractile cardiac activity.     

Effect of chronic hypobaria on isolated tracheal preparation.

Isolated tracheal preparation (ITP) has been studied from rabbits adapted to 24 days simulated hypobaria (PB = 395 mmHg), corresponding to an elevation of 17,000ft (5,000m). During this daily hypobaric exposure, the growth of these animals was continuous and final hematocrit reached 70%. After 24 days of hypobaric exposure, the sensitivity of ITP was tested to acute hypercapnia and acute anoxia. Acute hypercapnia was induced by aerating a muscle chamber with a gas mixture of 85% oxygen and 15% carbon dioxide. During that time, the PCO2 of the experimental solution increased from 24 to 66 mmHg with a corresponding change of pH from 7.39 to 7.10. ITP from rabbits exposed to chronic hypoxia reveals a greater sensitivity to acute hypercapnia as measured by active tension (AT max) and rate of tension development (dT/dt). Acute anoxia was induced by aerating a muscle chamber with a gas mixture of 95% nitrogen and 5% carbon dioxide. During 20 min of these conditions, the Po2 decreased from 520 to 25 mmHg. Although the contractility diminished at approximately equal rates in both groups in response to acute anoxia, preparation from animals exposed to hypobaria showed statistically a significantly greater ability to recover from the anoxic state.     

Cardiac anoxia tolerance of carbon monoxide-poisoned, hypoxia-exposed and normal rats.

Under nitrogen anoxia heart rate (HR) persists at a high level for 1 min longer in rats exposed chronically to carbon monoxide and hypoxia than in unexposed control rats. Although declining sharply, HR of exposed animals continues higher than HR of controls during min 1-4 of anoxia. However, during min 5 and 6 of anoxia HR of CO-poisoned rats becomes similar to that of controls, while HR of hypoxia-exposed rats remains above control HR for 3 min longer. The data are discussed in light of cardiovascular changes induced by CO and hypobaric hypoxia.     

Effect of darkening the cotyledons on the growth and curvature of the sunflower hypocotyl: evidence of hydraulic signalling

When both cotyledons of light-grown sunflower seedlings (Helianthusannuus L.) were darkened by covering them with aluminium foil,the resulting increase in the rate of elongation of the hypocotylwas closely proportional to the associated reduction in seedlingtranspiration and to the increase in xylem water potential (_PX.Covering only one cotyledon induced curvature away from thatside. This response was associated with a higher _PX in the vascularbundles connected directly with the covered cotyledon than inthose connected with the illuminated cotyledon. The water contentof peripheral tissues of the hypocotyl below the covered cotyledonwas also higher than that of similar samples from below theilluminated cotyledon. These results are consistent with thehypothesis that the effect of darkening the cotyledons on thegrowth and curvature of the hypocotyl is mediated by hydraulicsignalling, characterized by transmission to the hypocotyl ofan increase in _PX resulting from the reduction in cotyledontranspiration. Key words: Cotyledons, Helianthus annuus, hydraulic signalling, hypocotyl, transpiration, water potential     

The Effect of Salinity on the Membrane Potential of Sunflower Roots

The effect of NaCl and Na₂SO₄ on the electrical potential difference(PD) across the membrane in the outer cortical cells of theroot of sunflower (Helianthus annuus) has been investigated.The effect on the PD of a range of concentrations of these saltsgiven as a shock treatment was compared with the long-term effectwhere plants were grown in a range of salinities for 2 weeks. Considerable effects on the PD were observed. In low concentrationsof salt (approximately 1 mM) the PD was enhanced whilst in highconcentrations there was a progressive reduction in the PD.Na2SO4 had a relatively greater effect on the PD than NaCl. Using a transient recorder it was possible to measure the PDacross the plasmalemma and the tonoplast separately. The PDacross the plasmalemma was found to be markedly affected bysalinity. The tonoplast PD was relatively small compared tothat across the plasmalemma and appeared to be little affectedby the salts.     

The role of hepatic glycogen stores in anaerobic metabolism in rats

Plasma levels of lactate and oxypurines markedly increased in both fed and fasted rats exposed to three acute anoxic states, cyanide poisoning, carbon monoxide poisoning and inhalation of oxygen-deficient gas, suggesting that the transition of aerobic to anaerobic metabolism occurred similarly in both groups. Plasma glucose level of fed rats increased 1.8-2.5 times after exposure to anoxia, whereas a remarkable hypoglycemia was induced by the exposure of fasted rats to anoxia. Hepatic glycogen stores in fed rats induced hyperglycemia, while exhaustion of the stores in fasted rats resulted in severe hypoglycemia during acute anoxia.     

Substituent effect of the stacking interaction between carbon monoxide and benzene

Noncovalent interactions (NCIs) between carbon monoxide and substituted benzene were investigated at the M06-2X/6-311++G(d,p) level. rThe results of interaction energy analysis indicated different effects for the electron-donating (–NH₂, –OH, –CH₃) and electron-withdrawing (–F, –CN, –NO₂) groups on the CO?PhX complex. Atoms in molecules analysis confirmed the NCIs between CO and PhX. NCI analysis revealed that these interactions belong to van der Waals interactions. The electron density shift of the complexes was investigated with electron density difference analysis. Ternary CO?PhX?Bz complexes were designed to study the interplay between CO?π and π?π stacking interactions.     

Photosynthetic Oxygen Production Facilitates Translocation of 11C-Labelled Photoassimilates from Tendrils and Leaflets of Pisum sativum L

The translocation profiles of ¹¹C-photoassimilates from eithertendrils or leaflets of the compound leaf of Pisum sativum weresimilar in shape, speed and susceptibility to blockage by chillingand heat girdling. When the feed leaf component was exposedto an anaerobic gas stream consisting of N₂ gas supplementedwith 40 Pa CO₂, the export of previously-fixed ¹¹C-photoassimilatesfrom both leaflets and tendrils continued in the light, butstopped in the dark. However, in the light, translocation of¹¹C-assimilates from the leaflet was rapidly blocked by a flowof pure N₂ (i.e. anoxia). Movement of ¹¹C-assimilates from theleaf of another C₃ plant, sunflower, was similar to that fromthe pea leaflet. In contrast to both laminar leaf components,export from the tendrils was stopped under pure N₂ only in thedark. Taken together the data suggest that photosynthetic O₂production facilitated the movement of ¹¹C-assimilates in theabsence of exogenous O₂. The differences observed between thetendrils and the leaflets exposed to pure N₂ could be attributedto the greater capacity of tendrils to produce and recycle CO₂to support photosynthetic O₂ production in the light. Key words: Pea, ¹¹C-translocation, anoxia, tendril, leaflet     

Biogenesis of carbon monoxide: production by fungi and seed plants in the dark

Fungi and angiosperm seeds and seedlings produce carbon monoxide in darkness when under a low oxygen—high carbon dioxide atmosphere. Peak yields of 40 to 90 nmol/g dry weight were measured after six days, declining thereafter. Peak rates of carbon monoxide (CO) production were observed in Agaricus and cucumber seedlings (0.65 and 0.91 nmol/g/hr, respectively). The addition to radish and cucumber seeds of an antibiotic mixture had little effect on the course of their CO production. We suggest that in addition to the well known process of CO production in leaves of terrestrial plants in light, there is a significant light independent source of the gas among smaller plants associated with the soil—surface and soil—air interface.     

Relationship between Coleoptile Elongation and Alcoholic Fermentation in Rice Exposed to Anoxia. II. Cultivar Differences

The relationship between coleoptile elongation and survivalvs. alcoholic fermentation of rice under anoxia is examinedusing eight cultivars differing in submergence tolerance. Anoxiawas imposed on either 1 or 4 d aerated seeds either by N₂ flushingsubmerged tissues or by incubating tissues in stagnant deoxygenatedagar at 0·1% w/v; the latter simulated the stagnant conditionsof waterlogged soil. Two cultivars that were most tolerant tosubmergence also had the greatest tolerance to anoxia, whilea submergence intolerant cultivar was also intolerant to anoxia. Coleoptile growth under anoxia was related to rates of ethanolsynthesis (R_E), however differences between growth during anoxiaand survival after anoxia indicated that post-anoxic injurymay also be important in rice seeds exposed to anoxia. The correlationbetween coleoptile growth and R_E measured on a tissue basisusing intact seeds was r² = 0·67 among six varietiesover 0-3 d anoxia. This correlation improved to about r² = 0·85using R_E of (embryos plus coleoptiles) over 0-3 d, or coleoptilesat 3 d after anoxia. Coleoptile growth of individual seeds wasusually poorly correlated to R_E in these cultivars at 2-3 dafter anoxia. When coleoptiles of similar lengths were obtainedfrom different cultivars using 4 d aerated seeds, there weredifferences in R_E and coleoptile growth which were related tocoleoptile growth during 3 or 5 d anoxia, either on a tissue(r² = 0·85) or a fresh weight basis (r² = 0·70-0·97respectively). Results are discussed in relation to factorswhich may limit ethanol synthesis in rice exposed to anoxiaand the importance of growth to the survival of seeds and matureplants during submergence in the natural environment.Copyright1994, 1999 Academic Press Anoxia, ethanol, alcoholic fermentation, Oryza sativa L., rice, submergence     

Effects of Anoxia on Phloem Loading in C3 and C4 Species

Changes in phloem loading rate were inferred from observationsof ¹¹C export from attached leaves of C₃ and C₄ monocots anddicots. Loading decreased under anoxia in C₃ leaves, but notin general in the leaves of either C₄ monocots or dicots inthe light. However, loading rate in the C₄ leaves did reduceif the leaf was also darkened or received no CO₂. We suggestthat insensitivity to anoxia in C₄ leaves is due to oxygen fromphotosynthesis which is retained in the bundle sheath at a concentrationsufficient to energize a phloem loading system. There may alsobe another system which is insensitive to anoxia since the effectsof shade and CO₂ deprivation were not always seen, and loadingwas not completely stopped by these treatments. Key words: Phloem loading, C₃, C₄     

Resting membrane potential and action potential of Nitella expansa protoplasts

Inside negative membrane potentials were observed for protoplastsobtained from Nitella expansa leaf internodal cells in mediacontaining 1 to 100 mM CaCl₂ using the microelectrode technique.The potential values were less negative than the membrane potentialof intact N. expansa leaf internodal cells. In addition, anaction potential consisting of two components—a fast componentand a slow component—was induced by electrical stimulationfor the protoplasts as well as the intact cells. (Received December 18, 1979; )