The Absorption of Ions by Excised Root Systems: II. OBSERVATIONS ON ROOTS OF BARLEY GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Barley plants were grown in complete culture solution and indeficiencies of phosphorus, nitrogen, or potassium for a periodof about 6 weeks. Excised roots of these plants were treatedwith a complete, aerated culture solution at 25? C. for varyingperiods of time, and the changes in respiration rate, phosphorus,nitrogen, potassium, sugars, and starch contents measured.
2. Therewere changes in fresh weight and dry weight of the excisedrootsduring treatment. The dry weight decreased with time butthewater-content changes were variable. There was a gain orlossof water by the roots according to the treatment.
3. In all casesthe deficient roots increased in content of theelement in whichthey were originally deficient. The roots ofthe plants suppliedwith full nutrient usually decreased incontent of phosphorus,nitrogen, and potassium, but exceptionsoccurred and the reasonsare discussed.
4. In most of the experiments described simultaneousloss of oneion and gain of another occurred.
5. Nitrogen-deficientroots accumulated nitrate when exposed toa complete nutrientsolution, and some of this was assimilatedwith formation ofprotein. Under similar conditions nitrogen-richroots decreasedin nitrogen content and proteolysis took place.
6. There wasa rapid fall in sucrose and reducing sugar contentof the excise'roots. The starch content was initially verysmall and showedlittle change with time.
7. The respiration rate declined withtime in all treatments exceptwhere a nitrogen deficiency existed.Here the respiration rateincreased to a maximum value at about8 hours and then fell.This increase in rate is attributed toprotein synthesis. Noevidence of a ‘salt respiration’was observed evenwhen active uptake of phosphorus or potassiumwas occurring.
8. In most instances the carbon dioxide evolvedin respirationgreatly exceeded the carbon dioxide equivalentof the sugarconsumed in the same period. Exceptions were foundwith thenitrogen-deficient roots where less carbon dioxidewas evolvedthan the equivalent of sugar consumed. It is probablethat apart, at least, of the sugar unaccounted for was usedin proteinsynthesis.
9. Where the carbon dioxide of respirationwas in excess of theequivalent of sugar consumed, protein oramino-acid is the mostprobable substrate. Respiration rateis found to be relatedboth to nitrogen and sugar content.

     

The Absorption of Ions by Excised Root Systems: III. OBSERVATIONS ON ROOTS OF PEA PLANTS GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Pea plants were grown in complete culture solution and in deficienciesof phosphorus, nitrogen, or potassium for a period of about5 weeks. Excised roots of these plants were treated with a complete,aerated culture solution for varying periods of time and thechanges in respiration rate, phosphorus, nitrogen, potassium,sugar, and starch contents measured.
2. There were changes infresh weight and dry weight of the excisedroots during treatment.The dry weight decreased with time butthe water content changeswere variable. Uptake of water wascorrelated with uptake ofpotassium and sucrose content in someinstances.
3. There wasno evidence of a ‘salt respiration’ inthose caseswhere active accumulation occurred.
4. The rates of gain or lossof phosphorus, nitrogen, or potassiumat 0 hours, 8 hours, and16 hours were calculated and it wasfound that the rate dependedboth on content of element in theroot and the sugar cotent.There was very little evidence thatone element affected therate of uptake of another. Simultaneousloss of one elementand gain of another occurred in some instances.
5. The observationsappear to be best explained on the assumptionthat the absorbedions are fixed in the cells in the form ofloosely bound compoundsand that these compounds are formedfrom sugars.

     

Polyphenol Oxidase in the Respiration and the Salt Uptake of Storage Tissues3

The respiration and potassium uptake of beet and potato diskshave been measured in the presence of protocatechuic acid. Itis found that protocatechuic acid in a concentration of 10^–3to 3 x 10^–3 M at pH 6, stimulates both oxygen uptake andcarbon dioxide output. This stimulation of respiration is accompaniedby a reduction in potassium uptake. Experiments with carbon monoxide indicate that polyphenol oxidasemediates the ‘extra’ respiration in the presenceof protocatechuic acid, although this enzyme does not appearto play any part in the normal respiration, at least in 5 percent oxygen. These results are considered in relation to previousclaims concerning the role of polyphenol oxidase in salt uptakeand respiration of potato disks. Potassium uptake by potato disks is light-reversibly inhibitedby carbon monoxide, indicating the participation of cytochromeoxidase in salt uptake in this, as in other tissues.     

The Effects of Sugar and Potassium on Extension Growth in the Root

1. A new technique for studying extension growth in the root isdescribed which is based on excising a zone which extends 1·5–3·0mm. from the tip. Large numbers of these segments are culturedwith different nutrient fluids in the dark at 25° C. withcontinual shaking.
2. The effects of a large number of nutrientson the growth ofthe segments have been studied, but only two,sugar and potassiumions, have been found to have stimulatingeffects.
3. The effects of water, three concentrations of sugar,and oneof potassium in air, and with an atmosphere containing5 percent. oxygen have been studied in detail in connexionwith lengthincrease, sugar absorption, content of free sugar,cellulosecontent, dry weight, and respiration.
4. It has beenshown that with increasing concentration of sugarin the medium,the rate of growth, the time during which growthproceeds, theinternal concentration, respiration, dry weight,and celluloseformation all increase. Also that potassium stimulatesthe rateof growth and respiration, and that with per cent,oxygen allthe aspects studied are depressed.
5. It is suggested that thestimulation due to sugar may be attributedto an accelerationof water absorption with a complementaryincrease in celluloseformation. It is further suggested thatsugar accelerates waterabsorption by accumulating in the vacuoleand thus sustainingthe osmotic pressure of the vacuolar sap.It is further suggestedthat potassium stimulates growth byincreasing water absorptionthrough an effect on respiration.The effect of respirationin this connexion may be to promotethe transport of water directlyto enhance the osmotic pressureof the sap by inducing an accumulationof inorganic ions inthe vacuole.

     

Studies on the destruction of indole-3-acetic acid by a species of Arthrobacter II. Properties of the oxidation system

1. Some properties of the IAA-oxidizing activity of lyophilizedcells of Artkrobacter sp. were examined.
2. 1. IAA oxidationseems not to be catalysed by peroxidase, polyphenoloxidase,laccase or dehydrogenase, but by an oxidase systemdifferentfrom the one reported earlier.
3. 2. The optimal pH for the oxidizingsystem is ca. 6.0, and thesystem is comparatively stable atpH 5 to 10.
4. 3. The optimal substrate (IAA) level is 10^–3M.
5. 4. Activity is inhibited by metal-chelating reagents, suchassodium azide, potassium cyanide, sodium diethyldithiocarbamate,potassium xanthogenate and 8-hydroxyquinoline, and sulfhydrylreagents, such as iodoacetamide, monofluoroacetic acid, p-chloromercuribenzoate,isatin, ß-naphthoquinone and ß-naphthoquinone-4-sulfonate.Hydroxybenzoic acid, sulfosalicylic acid and 2,4-dichlorophenolare also inhibitory.
6. 5. None of the IAA analogs tested (indole,skatole, 2,3-dihydroxyindole,indole-3-aldehyde, -3-carboxylicacid, -3-propionic acid, -3-lacticacid, -3-butyric acid, 5-hydroxyindole-3-aceticacid and D,L-tryptophan) are oxidized by the cells, and someanalogs (indole-3-carboxylicacid, -3-propionic acid, -3-butyricacid, 5-hydroxyindole-3-aceticacid, naphthalene-acetic acidand 2,4-D) are inhibitory at comparativelyhigh concentrations.
7. 6. The oxidizing activity is not stimulated by Mn⁺⁺ and isinhibitedby Co⁺⁺, Cu⁺⁺ and Hg⁺⁺.
8. 7. The oxidizing activitydisappears completely within 6 hrat 30, but is kept unchangedat least for two weeks at –20.

(Received August 7, 1967; )     

Specificity and Reversibility of the Bicarbonate Effect on Hexose Uptake by Maize Root Tips

The inhibition of hexose uptake by bicarbonate ions was investigatedin detail in order to test the specificity and reversibilityof the effect and to compare it with those of other electrolytes.The degree of inhibition was similar at pH 7.0 and pH 8.0. AtpH 4.5 no influence of a high concentration of CO₂ on 3-O-methylglucoseuptake was found. Therefore, the inhibition of hexose uptakeby bicarbonate cannot be explained by consequences of CO₂ influx.The inhibition of sugar absorption by calcium and potassiumions was similar to that exerted by bicarbonate in so far asit was observed at higher pH only. The inhibition exerted bysodium salts of different monovalent weak acids was limitedto lower pH and needed some time to become established or reversed.The bicarbonate effect was independent of time and reversiblewithout a lag phase. Sodium salts of strong mineral monovalentacids did not differ significantly in their effect on sugaruptake. Bicarbonate inhibited phosphate uptake in a similarmanner to hexose uptake but strongly stimulated the absorptionof potassium. The bicarbonate effect is assumed to result froma change in the degree of coupling of secondary active transportto the proton pump. Key words: Inhibition, Transport coupling, pH, Proton pump     

The Relationship between Metabolism and the 'Exchangeability' of Ions in Plant Tissues2

The uptake of the rubidium ion by well-washed disks of carrotparenchyma has been determined at 0·2° C and 25°C., in the presence and absence of 10^–4M. dinitrophenol,from solutions of rubidium chloride containing 0·5 and5·0 meq./l. Readily-exchangeable and non-exchangeablefractions were separately indentified. The lowering of temperature and application of DNP reduced themagnitude of both ion fractions at each of the two concentrationsof rubidium chloride. Despite the fact that the uptake of ionsinto an exchangeable form at 5·0 meq./l. was about 3times greater, the combined effect of low temperature and thepresence of DNP reduced this fraction by a relatively constantabsolute amount. Under the same conditions the uptake of ionsinto a non-exchangeable form from each concentration was reducedby approximately the same percentage. Over a 6-hour period the rate of uptake of rubidium into a non-exchangeableform at 25° C. was relatively constant, whereas at 0·2°C. there was an initial rapid uptake lasting for about 60 minutesfollowed by a slow steady uptake. The Q₁₀ of this latter processmeasured after 360 minutes was 2·3. It is concluded that an appreciable part of the capacity ofthe tissue to hold ions by exchange is dependent on concurrentmetabolism. The significance of measurements of exchangeability in the interpretationof mechanisms of ion uptake is discussed.     

Further studies on potassium uptake rhythm in the long-day duckweed Lemna gibba G3 with special reference to vegetative growth

Some properties of the circadian rhythm in potassium uptakeof flow medium culture of the long-day duckweed Lemna gibbaG3 were examined.

1. In total darkness, the rhythm faded out in ca. 48 hr; it restartedon transfer to continuous light. Under low-intensity light (below700 lux), the rhythm was damped rapidly
2. The rhythm appearedregardless of the potassium concentrationin the culture medium(from 10/m to 2 HIM). The amplitude, butnot the period, ofthe rhythm was influenced by the ambientpotassium concentration.
3. Alteration in the light intensity or medium composition causeda change in the growth rate without modifying the period ofthe rhythm.
4. These results indicate that potassium uptake rhythmin thisduckweed is typical light-on rhythm, which has no directrelationwith the rate of vegetative growth and requires lightenergyfor its duration.

¹Present address: Aichi-Gakuin University, Chikusa-ku, Nagoya464, Japan. ²Present address: National Institute for Basic Biology, Okazaki,Aichi 444, Japan. (Received February 1, 1979; )     

Light-induced changes of b-type cytochromes in the electron transport chain of Euglena chloroplasts

Light-induced changes of b-type cytochromes in Euglena chloroplastswere studied spectrophotometrically.

1. In the dark and at pH 6.5, most of the cytochrome 558 in chloroplastswas in the reduced state, and most of the cytochrome 563, inthe oxidized state. Illumination of chloroplasts at pH 6.5 induceda rapid, but slight oxidation of cytochrome 552 and cytochrome558. The magnitude of photooxidation of cytochrome 558 was greatlyenhanced by the addition of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea(DCMU). The rate of photooxidation in the presence of DCMU wasstimulated by the addition of 0.15 µM Euglena cytochrome552, or 100 µM methyl viologen.
2. Euglena chloroplasts,incubated at 55°C for 5 min showedno significant absorbancechanges for about 10 min after theonset of illumination. However,greater photooxidation of cytochrome558 was observed afterprolonged illumination, or in the presenceof DCMU or ethylenediaminetetraaceticacid (EDTA). Similar resultswere obtained with chloroplastspre-treated at pH 9.0–10.0for 5 min.
3. At pH 9.5, andin the dark, both cytochrome 563 and cytochrome558 were inan almost reduced state. On illumination at thispH, both cytochromeswere photooxidized, with a complicatedkinetics, showing aninitial rapid and small absorbance decrease,followed by a stagnantphase of temporary retarded reaction.In the presence of DCMUor EDTA, photooxidation proceeded rapidlywithout a stagnantphase.
4. At pH 6.5 cytochrome 558, on cessation of illumination,wasquickly reduced to the initial level. At pH 9.5, there wasalsoappreciable re-reduction of cytochrome 558 and 563 whenthelight was turned off at an early stage of illumination.Theamounts of re-reduction of the cytochromes in the subsequentdark period, however, decreased as photooxidation of cytochromesproceeded. This decrease was accelerated by the presence ofDCMU.
5. At pH 9.5 ascorbate and manganese served as electrondonorsfor die DCMU-sensitive photooxidation of cytochromes558 and563.
6. Experimental results are discussed with specialreference tothe occurrence of two pools of electron carriers,one at thereducing side and the other at the oxidizing sideof photosystem2. The role of manganese in the latter pool ofelectron carriersis also discussed.

(Received March 11, 1970; )     

The relationship of sodium uptake,potassium rejection,and skin potential in isolated frog skin

1. Isolated surviving frog skin, when bathed with the same kind of diluted Ringer's solution on both sides, shows a negative correlation between net active salt uptake by the epithelium and spontaneous skin potential. Average values of 0.15 to 0.86 µeq. x hr.^–1 x cm.^–2 were measured and correlated with average skin potentials ranging from 107 to 25 mv. 2. Sodium uptake exceeded chloride uptake by about the same amount, irrespective of the height of the skin potential. 3. The same skins which exhibited a negative correlation between net uptake of sodium chloride and skin potential showed a positive correlation between net potassium rejection from the epithelium and skin potential, for voltages above 30 to 40 mv. In skins of voltages lower than this, potassium ions were taken up rather than rejected. Average values for rejection of +11.8 to –0.8 centi-µeq. x hr.^–1 x cm.^–2 were measured. 4. Net fluid uptake, associated with active uptake of sodium chloride, was small and occurred in the direction of the salt uptake. No dependence of net fluid uptake upon skin potential was observed. 5. Skins of winter frogs, pretreated with a commercial purified ACTH preparation, were less active than their respective controls with regard to uptake of sodium chloride. Rejection of potassium was the same in treated and untreated skins. Posterior pituitary factors, as possible contaminants, did not account for the effect of the ACTH preparation. 6. DOCA, DOC, and cortisone did not alter the normal correlation referred to under (1) and (3). 7. In interpreting the experimental results on theoretical grounds, it is suggested (a) that in normal skin, it is the variation in the electric conductance in skin of chloride ions which essentially, although not exclusively, determines the rate of net uptake of sodium chloride, (b) that a factor in the ACTH preparation used, possibly ACTH itself, may have lowered the electric conductance in skin of sodium ions either truly or apparently, (c) that potassium ions are treated by the skin primarily as passive ions. There is some indication that potassium ions are also actively taken up by the epithelium of skin.     

ROLE OF CALCIUM IN POTASSIUM UPTAKE BY PLANT ROOTS

The effects of EDTA·Mg or GEDTA·Mg on the uptakeof nutrient ions, the release of Ca⁺⁺ and nucleotides into themedium and the nucleic acid contents in rice and red bean rootswere investigated.

1. Both EDTA and EDTA·Mg induced similarly the release ofCa from roots.
2. EDTA·Mg as well as EDTA brought abouta significant repressionin K uptake, but had an insignificantor no effect on P, NH₄and NO₃ uptakes. EDTA·Ca did notrepress K, P, NH₄ andNO₃ uptakes.
3. EDTA or GEDTA acceleratedthe degradation of nucleic acid andthe release of nucleotides,while EDTA·Mg or GEDTA·Mghad no such effect.

These results indicate that the indispensable role of intracellularCa in K uptake does not appear to be directly associated withRNA metabolism. (Received July 29, 1965; )     

An Effect of pH and Bicarbonate on Salt Accumulation by Disks of Storage Tissue

1. The uptake of potassium chloride by disks of several storagetissues has been determined from solutions at alkaline pH valuesand compared with that form solutions at pH 6.5. The stimulationof cation uptake under the alkaline conditions which has previouslybeen obtained with beet tissues was observed with some of thesetissues to a greater or lesser extent. 2. It is concluded that it is the accumulation of anions present in alkaline solutions which generally promotesthe uptake of cations; tissues which do not show the ‘pHeffect’ accumulate very little in the presence of the Cl^- anion. 3. In some cases the alkaline pH values also stimulated anionuptake. This was especially true in artichoke in which the absorptionof both ions was stimulated by approximately the same amount.It is concluded that this represents either a true pH effector a direct effect of anions on the overall salt sccumulation mechanism rather than an indirect effect throughorganic acid synthesis. 4. The experiments reveal a cation/anion ratio of approximatelyI:I when the uptake of ions is taken into consideration. It is suggested that this ratio may be more frequent then isgenerally accepted and that the uptake of CO₂ (converted toan anion in the tissue) may take the place ions at lower pH values. 5. The deleterious effects of frequently observed on growth contrast with the stimulations of salt absorptionobtained here; the rapid increase in the concertration of cationsand/or organic acid anions associated with HCO uptake may insome way be responsible for this.     

Studies on the destruction of indole-3-acetic acid by a species of Arthrobacter I. On the induction of the enzyme responsible for the destruction

1. The induction of an IAA-destroying enzyme in Arthrobacter sp.that can utilize IAA as its sole source of carbon and nitrogenwas investigated.
2. 1. The enzyme was most effectively inducedby 10–³ to2x10–³ M IAA, at pH 6.5.
3. 2. All testedIAA analogs were unable to induce the enzyme.Analogs otherthan indole-3-lactic acid were rather inhibitoryon the inductionwith IAA.
4. 3. The induction period was shortened with the ageof culturein both polypeptone and acetate media.
5. 4. Pretreatmentof the bacterium with IAA caused a shorteningof the inductionperiod.
6. 5. The induction was inhibited by various antibiotics,aminoacid analogs and nucleobase analogs.
7. 6. The inductionwas less remarkable in actively proliferatingcells than itwas in slowly proliferating ones.

(Received July 1, 1967; )     

Auxin-induced extension of the isolated epidermis of light-grown pea epicotyls

1. The effect of IAA and FC on the extension of isolated epidermisof light-grown Alaska pea epicotyls was studied under differentconditions with an extension apparatus. The following resultswere obtained.
2. The epidermis extended in response to low pHbuffer solutionof 1–10 mM, maximum extension being achievedat pH below5.5.
3. IAA, 5 mg/liter, caused, although not consistently,an extensionof epidermal strips in 1 mM buffer, but not at10 mM.
4. Consistent extension of the isolated epidermis dueto IAA wasobtained by addition of GTP, ATP, ITP or UTP (sodiumsalts),but not nucleosides, nitrogen bases or sugars.
5. A fungaltoxin, FC, at 10^–5 M induced extension of theepidermiswithout addition of the nucleoside triphosphates.
6. IAA andFC caused H⁺ extrusion in peeled epicotyl segments bothin thepresence and absence of GTP. IAA caused appreciable H⁺extrusionin the isolated epidermis only in the presence ofGTP, whereasH⁺ extrusion by the epidermis was induced by FCeven in theabsence of GTP.

From these results, we concluded that IAA induces extensionof the isolated epidermis under the above conditions throughthe mediation of H⁺ ions. (Received July 12, 1976; )     

Osmoregulation in Rhizobium meliloti: inhibition of growth by salts

A defined medium of low osmolarity was developed permitting growth of Rhizobium meliloti with generation times of approximately 2.8 h doubling^-1. The effects of sodium, potassium, magnesium, ammonium, chloride, sulfate, phosphate, bicarbonate and acetate ions on the growth rate of R. meliloti were determined. Sodium, potassium and ammonium ions had little effect on growth at concentrations of 100 mEq or less; magnesium ion inhibited growth severely at concentrations of 50 mEq (25 mM). Of the anions, chloride and sulfate appeared to have little effect while phosphate, bicarbonate, and acetate inhibited growth at concentrations of as little as 25 mEq. The addition of proline, glutamate, or betaine to cells growing in inhibitory concentrations of NaCl did not relieve the inhibition. When grown in the presence of inhibitory levels of NaCl, the intracellular concentration of glutamate but not of proline or gamma amino butyric acid increased 5-fold.     

HIGH AFFINITY CHOLINE UPTAKE: IONIC AND ENERGY REQUIREMENTS

Abstract— High affinity choline uptake into rat hippocampal synaptosomes was examined at 37°C when various ions were deleted from normal Kreb's-Ringer media. When sodium chloride was replaced by sucrose, lithium chloride, cesium chloride or rubidium chloride, choline uptake was markedly reduced. When the sodium concentrations of the Kreb's media were gradually reduced to zero, the uptake was gradually reduced in parallel. A kinetic analysis performed at low and normal sodium concentrations revealed changes in K_m and V^max values. When several non-chloride sodium salts were utilized, the uptake was reduced in all cases suggesting also a chloride-dependence in addition to the sodium-dependence. Omission of calcium chloride or magnesium sulfate from the media did not alter uptake. Sodium-dependent choline uptake was examined over a range of potassium concentrations (0–35 DIM). It was found that uptake was maximal between potassium concentrations of 0.35–4.8 mm but was reduced at both lower and higher potassium concentrations. The kinetics of uptake were examined under varying potassium concentrations, and at low potassium, only a change in V_max was observed while at high potassium concentrations, there were changes in both K^m and V^max values. Preincubation and incubation of synaptosomes with 0.1 m -ouabain, 0.1 mm -2,4-dinitrophenol and 1 mm -KCN caused a reduction in sodium-dependent uptake. When dextrose was omitted from the preincubation and incubation media there was also a reduction in sodium-dependent uptake. By contrast, the sodium-independent uptake was unaffected by the metabolic inhibitors or omission of dextrose, and had a very low Q₁₀. When various incubation temperatures were utilized in uptake experiments, the Q¹⁰ for the interval 37-27°C was 2.7 and the activation energy was 22.7 kcal/mol. Slightly different ionic dependences were observed when animals pretreated with pentobarbital of oentylenetetrazol were utilized as the source of synaptosomes.     

CHANGES IN RESTING POTENTIAL AND ION ABSORPTION INDUCED BY LIGHT IN A SINGLE PLANT CELL

1. Effect of light on ion absorption and resting potential of theinternodal cell of Nitella flexilis was investigated under variousconditions.
2. On illumination, the resting potential increasedby about 30mVin 10^–4 M KCl and by about 60 mV in 10^–4M NaClsolution. A similar photoelectric response was also observedin 10^–3 M KCl, 10^–2 M CaCl₂ and 5 x 10^–2 MCaCl₂ solutions, but not at all in 10^–2 M KCl solution.
3. Absorption of ions by the cell took place in parallel withthelight-induced change in resting potential.
4. Red and bluelights were very effective in increasing the restingpotential,while green light was almost ineffective. These differenteffectsof color lights were in good agreement with their effectsinincreasing the osmotic value of the cell.
5. The photoelectricresponse was not affected by phenylurethane,which, on the otherhand, strongly inhibited the light-inducedion absorption.
6. Theuptake of ions by the cell from the external medium intothevacuole is assumed to proceed in two different steps: thefirstis the process involving the ion movements across theoutermostplasmalemma, and the second is that involved in thetransportof ions through the cytoplasmic layer and tonoplast.The formerprocess is considered to be influenced by the increasein restingpotential probably caused by the light absorbed bychlorophyll.The process was, however, suggested to be independentof photosynthesis.On the other hand, the latter process issupposed to be relatedto photosynthesis. A discussion was madealong this line.

(Received July 26, 1962; )     

The mechanism of phosphate permeation in purified bean mitochondria

The permeability properties and mechanism of Pi transport wereinvestigated in purified bean mitochondria.

1. Purified bean mitochondria are impermeable to small moleculesand ions. However, Pi, arsenate, acetate and formate can enterthe osmotically active space of bean mitochondria.
2. Nigericinor the association of valinomycin and FCCP cause mitochondrialswelling in isoosmotic potassium phosphate.
3. The SH-blockingreagents mersalyl, pHMB and NEM inhibit variousmitochondrialfunctions dependent on the translocation of Piand arsenateacross the membrane. These include the respirationstimulatedby ADP, Ca²⁺+Pi, and K⁺+valinomycin +Pi; the swellingin ammoniumphosphate medium and, in the presence of nigericin,in potassiumphosphate medium; the energy-linked yalinomycin-inducedswellingand the subsequent CICCP-induced shrinking. The uncoupler-stimulatedrespiration, as well as the other processes when acetate issubstituted for Pi, are not influenced by SH reagents.
4. Mersalyland pHMB cause complete inhibition at about 20 nmoles/mgprotein,whereas, NEM is effective at about 1 µmole/mgprotein.The inhibition by mersalyl and pHMB, but not that byNEM, issigmoidal and reversed by 2-mercaptoethanol. Non-inhibitoryamounts of mersalyl protect the Pi transport from irreversibleinhibition by NEM.
5. We concluded that a carrier-mediated transportsystem for Piis present in bean mitochondria, and that someof its propertiesare similar to the Pi carrier of animal mitochondria.

(Received June 5, 1975; )     

Chloride conductance of the Amphiuma red cell membrane

Summary Like most other red cells, the giant erythrocytes ofAmphiuma means possess a system for rapid exchange of chloride across the membrane. Also, there are indications that the net transport of chloride in these cells is slow. The size ofAmphiuma erythrocytes allows direct measurements of membrane potential with microelectrodes. The present work exploits the possibility that such measurements can be used to give a quantitative estimate of the chloride conductance (G _Cl) of the Amphiuma red cell membrane. The membrane potential was measured as a function of extracellular chloride concentration (5–120mM), using an impermeant anion (Para-amino-hippurate) as a substitute. Furthermore, the effect of different pH values (6.0–7.2) was studied. For each extracellular chloride concentration the membrane potential was determined at a pH at which hydroxyl, hydrogen, and bicarbonate ions were in electrochemical equilibrium. From these membrane potentials and the corresponding chloride concentrations in the medium (at constant intracellular ion concentrations), theG _Cl of the membrane was calculated to be 3.9×10^–7 {ie27-1} cm^–2. This value is some six orders of magnitude smaller than that calculated from the rate of tracer exchange under equilibrium conditions. The experimental strategy used gives the value for a partial transference number which takes into account only ions which arenot in electrochemical equilibrium. Whereas this approach gives a value forG _Cl, it does not permit calculation of the overall membrane conductance. From the calculated value ofG _Cl it is possible to estimate that the maximal value of the combined conductances of hydroxyl (or proton) and bicarbonate ions is 0.6×10^–7 {ie27-2} cm^–2. The large discrepancy between the rate of exchange of chloride and its conductance is in agreement with measurements on human and sheep red cells employing the ionophore valinomycin to increase the potassium conductance of the membrane. The results in the present study were, however, obtained without valinomycin and an accompanying assumption of a constant field in the membrane. Therefore, the present measurements give independent support to the above mentioned conclusions.     

Evaluation of antifungal activity of food additives against soilborne phytopathogenic fungi

The efficacy of eight food additives as possible alternatives to synthetic fungicides for the control of soilborne pathogens, Fusarium oxysporum f. sp. melonis, Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was evaluated in this study. A preliminary selection of food additives was performed through in vitro tests. The ED₅₀, minimum inhibition concentration (MIC), and minimum fungicidal concentration (MFC) values showed that ammonium bicarbonate and potassium sorbate were more toxic to soilborne pathogens compared to other food additives with few exceptions and, therefore selected for further testing in soil. The inhibitory and fungistatic efficacy potassium sorbate were higher than that of ammonium bicarbonate in in vitro tests. Potassium sorbate completely inhibited F. oxysporum f. sp. melonis, M. phaseolina, and R. solani at 0.6% in soil tests. In contrast ammonium bicarbonate at 0.6% was inferior compared to potassium sorbate. Ammonium bicarbonate achieved to control all fungi at 2% that is the highest concentration used in this study. Potassium sorbate showed higher toxicity to all fungi compared to ammonium bicarbonate in soil tests. Both ammonium bicarbonate and potassium sorbate increased the pH of soil. The rate of pH increase was higher in ammonium bicarbonate.