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1.
Effects of Cl and other anions on the rate of HILL reactionin Euglena chloroplasts were investigated. Cl acceleratedthe reaction rate with ferricyanide as HILL oxidant; Br,F and I were also effective; NO3, PO42and SO42 were less effective. Divalent cations, Ca2+and Mg2+, were also highly effective. The promoting effectsof these ions were highly dependent on pH and the nature andconcentration of the HILL oxidant used. Accelerating effectsof the ion increased with decreasing concentrations of ferricyanide.Generally, the stimulating effect of Cl was much moremarked at pH 77.5, with little effect at pH 5. Thus,the pH-activity relationship in the HILL reaction is more orless markedly modified by addition of ions. Cl, and other anions, accelerated the reaction by affectingonly the dark rate-limiting portion of the HILL reaction; thelight reaction constant remained uninfluenced. We inferred thatsome reaction step, at which ferricyanide receives electronfrom photosystem 2, is accelerated by Cl and other ions.Cl effects were rather small, or undetectable, with DPIPor p-benzoquinone as oxidants. (Received January 8, 1970; ) 相似文献
2.
Ricinus communis L. var. Gibsonii was grown in Long Ashton nutrientmedium with either 12mol m3 NO3 or 8.0 mol m3NH+4 as N source. Two plants from each N treatment were harvestedtwice a week and analysed for C, N, P, S, NO3, SO24ClK+Na+, Ca2+ Mg2+ and ash alkalinity. Statistical analysis of thedata showed that the effect of age and N source was differentfor the chemical variables analysed. Thus [Na+] was unaffectedby age or N source, and for both N sources [Mg2+] started atthe same level and decreased at the same rate as the plantsmatured. With NH+4 as N source, [SO24] was higher thanwith NO3, but did not alter with age. The concentrations,in mmol g1 dry wt, of C, organic N, K+ and Ca2+ weredifferent for the two N sources, but the levels of these variablesaltered with age in the same way for both N sources; i.e. therewas no age x N interaction. In the case of P, NO3, Cl and COO, however,age-related variations were different for the two N sources.It is concluded, inter alia, that [Na+] is determined by external[Na+] alone, and that K+, Ca2+ and Cl are the inorganicions actively involved in charge balance during ion uptake bythe roots. Key words: Ontogeny, Chemical composition, Plant nutrition 相似文献
3.
Diurnal K+ and Anion Transport in Phaseolus Pulvinus 总被引:1,自引:0,他引:1
Diurnal movement of Phaseolus leaf is caused by deformationof the laminar pulvinus located at the joint of the leaf bladeand the petiole. The plants were cultured in solutions withvarious ion compositions, and changes of K+, Na+, Ca2+, Mg2+,Cl, NO3 and P1 concentrations both in the upperand lower parts of the laminar pulvinus were measured. Culturein 10 mM KCl solution caused an increase in K+ and Clconcentrations both in the upper and lower parts without anysignificant change in the concentration of NO3; culturein 10 mM KNO3 solution caused an increase in K+ and NO3concentration without any significant change in the concentrationof Cl; and culture in 10 mM KH2PO4 solution caused anincrease in K+ and P1 concentrations without any significantchange in the concentrations of NO3- and Cl. K+ moved from the upper to lower parts or from the lower toupper parts diurnally in all plants cultured in any solutionmentioned above. The main inorganic anion that accompanied thisK+ movement was Cl in KCl solution, and NO3 inKNO3 solution. When the seedlings were cultured in distilledwater or in KH2PO4 solution, neither Cl NO3 norP1 accompanied this K+ movement. In these cases, mainly H+ and/ororganic anions are supposed to move in exchange for and/or incombination with K+ movement. (Received November 8, 1982; Accepted June 13, 1983) 相似文献
4.
Nitrate Inhibition of Chloride Influx in Barley: Implications for a Proposed Chloride Homeostat 总被引:6,自引:0,他引:6
Net accumulation of Cl by intact barley plants was virtuallyeliminated in roots and reduced by 40% in shoots when externalmedia (0.5 mol m3 CaSO4 plus 05 mol m3KCI) were supplemented with 0.25 mol m Ca(NO3)2. Plasmalemma36Cl influx (oc) was shown to be insensitive to externalNO3- in plants which had previously been grown in solutionslacking 3, but oc became sensitive to NO3-after a lagperiod of 36 h. Kinetic analyses revealed that the inhibitionof 36C1 influx by external NO3- was complex. At 0.25mol m3 NO3- the Vmax for Cl influx was reducedby greater than 50%, with insignificant effects upon Km. At0.5 mol m3 NO3- there was no further effect upon Vmaxbut Km for influx increased from 38±5 mmol m3to 116±26 mmol m3. By contrast, Cl effluxwas found to be insensitive to external NO3-. A model for theregulation of Cl influx is proposed which involves bothnegative feedback effects from vacuolar NO3- +Cl) concentrationand (external) NO3- inhibition of Cl influx at the plasmalemma.These combined effects serve to discriminate against Claccumulation, favouring NO3- accumulation, when the latter ionis available. Such observations are inconsistent with recentproposals for the existence of bona fide homeostats for chlorideaccumulation in higher plants. Key words: Nitrate inhibition, Chloride influx, Barley 相似文献
5.
MURALITHARAN MORLEY S.; CHANDLER STEPHEN F.; VAN STEVENINCK REINHARD F. M. 《Annals of botany》1992,69(5):459-465
Non-selected and Na2SO-, K2SO4- or KCl-selected callus culturesof Vaccinium corymbosum L. cv. Blue Crop were grown on mediasupplemented with 0, 25 and 50 mM Na2SO4 (non-selected and Na2SO(-selectedonly), 0, 25 and 50mMK2SO4 (non-selected and K2SO4-selectedonly) or 0, 50 and 100 mM KCl (non-selected and KCl-selectedonly). On all media, growth of selected callus (on a fresh-weightor dry-weight basis) was greater than that of non-selected callus,and selected callus grew optimally on the level and type ofsalt on which it was selected. Selected callus was friable andmaintained a higher f. wt:d. wt ratio. Tissue water potentialin selected callus was more negative than in non-selected callus. Flame photometry and chloridometry showed Na+, K+ and Claccumulated in callus to concentrations equal to or greaterthan the initial concentration in the medium. Turbidometry showedthat tissue SO42- concentration was lower than the concentrationin the medium. In most cases selected callus accumulated moreNa+, Ksup, SO42 or Cl than non-selected callus.Vacuolar ion concentration was measured by electronprobe X-raymicroanalysis, and on most media selected callus had highervacuolar ion concentrations than non-selected callus. SO42and Cl were accumulated in the vacuoles at concentrationshigher than the external medium, but vacuolar Na+ concentrationdid not reach external concentration on Na2SO4 and on potassiumsalts was maintained between 12 and 17 mM. Vacuolar K+ concentration(approx. 142191 mM on no salt) decreased on Na2SO4 andincreased on K2SO4 and KCl. There was no precise correlation between total or specific ionaccumulation (Na+, K+, SO42 and Cl and fresh-weightyield. Results suggest that selection results in adaptationin response to decreased water potential of the medium. Vaccinium corymbosum, blueberry, electronprobe X-ray microanalysis, callus, in vitro selection, salt tolerance, KCl, K2SO4, Na2SO4 相似文献
6.
Lamaze, T., Sentenac, H. and Grignon, C. 1987. Orthophosphaterelations of root: NO3effects on orthophosphate influx,accumulation and secretion into the xylem.J. exp. Bot.38: 923934. Orthophosphate (Pi) accumulation by barley (Hordeum vulgareL.) roots was specifically inhibited by NO3 as comparedto Cl and SO42 , and Pi secretion into the xylemwas stimulated. The inhibition of Pi accumulation by NO3was also observed in roots of intact photosynthesizing horsebean(Vicia faba L.), rice (Oryza sativa L.) and soybean (Glycinemax L.) plants. NO3 effects on Pi transport by rootswere more thoroughly investigated with corn (Zea mays L.). Theywere due to intracellular NO3. Pi secretion was stillstimulated by NO3 after Pi withdrawal from the absorptionsolution. 32Pi influx decreased during Pi accumulation, supportingthe hypothesis that this ion allosterically regulated its owntransport system by feedback control. This control was modulatedby other anions: the decrease was more pronounced in the presenceof nitrate. Chronologically, the depressive effect of NO3on 32Pi influx appeared after the inhibition of Pi accumulation.Furthermore, under conditions where Pi accumulation was notaffected by NO3, 32Pi influx and Pi secretion into thexylem became insensitive to the presence of nitrate. Our hypothesisis that the stimulative effect of NO3 on Pi secretionand the depressive one on 32Pi influx are the repercussionsof an increase in the Pi cytosolic concentration due to an NO3-induced decrease in Pi uptake by the vacuoles. Key words: Root, orthophosphate fluxes, orthophosphate accumulation, nitrate, ionic interaction 相似文献
7.
Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO3-nutrition for 51 d under control (0.05 mol m3Na+ and 10 mol m3 Cl) and saline (40 mol m3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K+, Na+, Mg2+, and Ca2+ and the anions Cl, NOJ,malate, phosphate, and SO42. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO2 from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K+, Na+, and Cl over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO3 uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO3reduction in the roots was specificallyinhibited. Uptake and xylem transport of K+ was more severelyinhibited than photosynthetic carbon gain or NO3 uptakeby the root. K+ transport in the phloem was even more severelyrestricted under saline conditions. Na+ and Cl flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K+ supply and astrongly increased phloem translocation of Na+ contribute tothe adverse effects of salt in this species. Restriction ofK+ supply occurs by diminished K+ uptake and even more by reducedK+ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K+, Na+, CI 相似文献
8.
The Ionic Relations of Acetabularia mediterranea 总被引:3,自引:0,他引:3
The concentrations of K+, Na+, and Cl in the cytoplasmand the vacuole of Acetabularia mediterranea have been measured,as have the vacuolar concentrations of SO4 andoxalate. The electrical potential difference between externalsolution, and vacuole and cytoplasm has been measured. The resultsindicate that Cl and SO4 are probably transportedactively into the cell, and that active transport of Na+ isoutwards. The results for K+ are equivocal. The fluxes of K+,Na+, Cl, and S04 into the cell and theeffluxes of Na+ and Cl have been determined. The Clfluxes are extremely large. In all cases the plasmalemma isthe rate-limiting membrane for ion movement. A technique isdescribed for the preparation of large, completely viable cellfragments containing only cytoplasm, with no vacuole. 相似文献
9.
With slight modifications, conventional assay procedures forK+, Na+, Ca2+, Mg2+, Cl, NO3, H2PO4, fructoseand fructose-yielding saccharides, and glucose were applicableto the extract of Phaseolus pulvini. About 10 ml of a hot-waterextract from about 30 mg fresh weight of the pulvini was sufficientfor separate measurement of the ions and saccharides named above. (Received August 7, 1979; ) 相似文献
10.
REED ROBERT H.; COLLINS JULIAN C.; RUSSELL GEORGE 《Journal of experimental botany》1981,32(2):347-367
Ion contents and concentrations (K+, Na+, Cl, Ca2+, Mg2+,SO24, NO3, HPOJ24, amino and organic acids)of P. purpurea have been studied in relation to salinity variation.Cells were shown to accumulate large amounts of K+ and Clagainst their respective gradients of electrochemical potentialin all dilute and concentrated seawater media. Active influxof SOJ24, NO3, and HPOJ24 is also suggested,while Na+ is actively excluded from cells under hyposaline andhypersaline conditions. The relative proportions of individualcomponents of the internal osmotic potential were found to changeaccording to the external salt concentration. KCL forms themajor fraction of j} in concentrated seawater media while K+-aminoacids form the major fraction in dilute seawaters. Other intracellularsolutes comprise less than 15% oftj, in all media. Unidirectional fluxes of K+ and Cl were studied by radioisotopicmeans. Fluxes of K+ and Cl are reduced in hyposalinemedia, as is absolute KCL content per cell. Intracelhilar KCLcontent was also found to be markedly dependent upon externalK+ concentration, rather than water potential. Changes in KC1levels induced by salinity variation occur over a 6 h period. 相似文献
11.
Osman, M. E-A. H. and El-Shentenawy, F. 1988. Photosyntheticelectron transport under phosphorylating conditions as influencedby different concentrations of various salts.J. exp.Bot. 39: 859863. The rate of light-induced electron transport by isolated spinachthylakoids under phosphorylating conditions, as affected bydifferent concentrations of Br, Cl, NO3,HCO3, SO42 and CO32 has been investigated.The results show that both low and high concentrations of HCO32stimulated the oxygen evolution capacity under phosphorylatingconditions, whereas only low concentrations of CO32,SO42 and Cl stimulated the oxygen evolution capacity.However, irrespective of concentration, both Br and NO3reduced this capacity. The rate of photosynthetic electron transportwas generally stimulated by addition of ADP, even in cases whereelectron transport was inhibited by addition of bromide andnitrate. The different concentrations of these anions also causedreduction of the power generated by proton pumping and usedfor phosphorylation. The greatest level of reduction was observedin the presence of high concentrations of Cl and HCO3. Key words: Spinach thylakoids, photosynthetic electron transport, phosphorylation 相似文献
12.
Diurnal regulation of NO-3 uptake in soybean plants IV. Dependence on current photosynthesis and sugar availability to the roots 总被引:1,自引:0,他引:1
Delhon Patricia; Gojon Alain; Tillard Pascal; Passama Lucien 《Journal of experimental botany》1996,47(7):893-900
The short-term dependence of NO3 uptake upon photosynthesisand sugar supply to the roots of soybean plants was investigatedin a series of experiments where CO2 availability, light intensityor conduction of phloem sap to the roots were severely limited.Removal of CO2 from the atmosphere or girdling of the stem equallyprevented the stimulation of NO3 uptake when plants weretransferred from darkness to the light. The effect of thesetwo treatments can be reversed by CO2 re-supply or by additionof 10 mM glucose in the nutrient solution, respectively. Glucosewas also more effective in stimulating NO3 uptake byintact plants in darkness than in light. Collectively, theseobservations are interpreted as evidence that the diurnal changesin NO3 uptake are due to decreased phloem transport ofphotosynthates in darkness. Accordingly, the magnitude of thesechanges was much dependent on starch accumulation in the leavesat the end of the photo-period. Shading the plants lowered thisaccumulation, and resulted in an amplification of the diurnalchanges in NO3 uptake. These results are discussed inconnection with the hypothesis that the carbon-dependent plasticityof the night/day ratio of NO3 uptake is an importantfeature of the co-ordination of the acquisition of N and C bythe plant. Key words: Glycine max, light/dark cycle, NO3 uptake, C and N acquisition 相似文献
13.
H+ translocation driven by NO3, NO2 and N2O reductionswith endogenous substrates in cells of Rhodopseudomonas sphaeroidesforma sp. denitrificans was investigated by the oxidant pulsemethod. Upon injection of nitrogenous oxides to anaerobic cellsin darkness, an alkaline transient in the external medium wasobserved, followed by acidification. The alkaline transientwas enhanced by carbonyl cyanide m-chlorophenylhydrazone. When a viologen dye was used as an electron donor in the presenceof 1 mM Af-ethylmaleimide and 0.1 mM 2-n-heptyl-4-hydroxyquinoline-N-oxideto preclude respiration-linked H+ extrusion, addition of KNO3,KNO2 and N2O caused only a rapid alkalinization. The H+ consumptionstoichiometries, H+/2e ratios for NO3 reductionto NO2, NO2 reduction to 1/2 N2O and N2O reductionto N2 were 1.90, 3.18 and 2.04, respectively.These values agreed well with the fact that all reductions ofnitrogenous oxides in denitrification occur on the periplasmicside of the cytoplasmic membrane. When corrected for H+ consumption in the periplasm, the H+ extrusionstoichiometries, H+/2e ratios with endogenous substratesin the presence of K+/valinomycin for NO3 reduction toNO2, NO2 reduction to 1/2 N2O and N2O reductionto N2 were 4.05, 4.95 and 6.01, respectively. (Received August 4, 1982; Accepted January 13, 1983) 相似文献
14.
Ion Composition of the Chara Internode 总被引:2,自引:0,他引:2
Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K+, Na+, Ca2+, Mg2+, Cl, NO3 and H2PO4.Assuming that the volume of the cytoplasm Vp is 10% of thatof the whole cell V, the concentrations of K+, Na+, Ca2+, Mg2+,Cl, NO3 and H2PO4 in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K+, 111; Na+, 47; Ca2+, 4.4; Mg2+, 8.9; Cl,91; NO3, 3.3 and H2PO4, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when Vp/V = 5%. (Received May 18, 1987; Accepted September 29, 1987) 相似文献
15.
The Dependence of Calcium Transport and Leaf Tipburn in Strawberry on Relative Humidity and Nutrient Solution Concentration 总被引:1,自引:0,他引:1
Strawberry plants were grown in controlled-environment cabinetswith different day-and-night relative humidities, in nutrientsolutions of different osmotic potential and different calciumconcentrations. Leaf calcium (% d. wt.) depended strongly on leaf age and waslowest and very sensitive to environment when the leaf was emergingfrom the bud. Calcium in the emergent leaf was greatest andtipburn least when plants were grown in humid nights (VPD usually< 100 Pa) and weak nutrient solutions (osmotic potentialabout 25 kPa). Such plants guttated freely. In contrastplants grown in dry nights (VPD, c. 600 Pa) never guttated,had small concentrations of calcium in emergent leaves and sufferedtipburn. The behaviour of plants transferred between humiditytreatments rapidly reflected the new conditions. Increasingthe osmotic potential of the nutrient increased tipburn anddecreased calcium in emergent leaves even though the nutrientcontained more calcium. When the calcium concentration in the emergent leaf exceeded0.07 per cent of d. wt, tipburn was never seen; below 0.05 percent tipburn was usually severe. These results suggest that pre-emerged, and therefore non-transpiring,leaves depend for their calcium on water flow arising from rootpressure at night. After leaf emergence, calcium intake intoleaves was promoted by dry days, indicating that calcium wasthen supplied by transpirational water flow. Humid nights, drydays and weak nutrient solutions minimize the risk of leaf tipburnin strawberry. Fragaria ananassa Duch., strawberry, tipburn, calcium transport, relative humidity, nutrient supply, guttation 相似文献
16.
Ion and saccharide concentrations in the upper and lower partsof the laminar pulvinus of the primary leaf of Phaseolus vulgariswere measured in relation to the circadian movement. Concentrations of K+, Na+, Ca2+, Mg2+, Cl, organic acid,NO3, H2PO4, fructose and fructose-yielding saccharidesin the pulvinus were 75120, 0.30.7, 58,612, 4060, 6073, 1935, 29and 15 mM, respectively, and the osmotic pressure ofthe pulvinus was considered to be due to these ions. The cell volume in the expanding part was larger than that inthe contracting part. The change of the cell volume alteredthe molar concentration in the cell sap and therefore the amountof solutes actually transported from the upper to the lowerpart and vice versa was estimated from the concentration expressedin moles per gram of dry weight. Results showed that K+, Cl, organic acid (or H+) andNO3 moved from the upper to lower parts or vice versain the pulvinus in relation to its deformation, keeping theelectroneutrality among those ions, whereas Ca2+ and Mg2+ didnot move. The difference in the K+ concentration between theupper and lower parts when the leaf was up or down amountedto 30% of the whole osmotic pressure. This lead to the conclusionthat the endogenous clock-controlled unequal distribution ofK+, Cl, organic acid (or H+) and NO3 in the pulvinuscould be the force for the circadian leaf movement. (Received August 7, 1979; ) 相似文献
17.
In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK2s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m3 nitrogenas (NH4)2SO4. Initial pH of each solution was adjusted to theappropriate buffer pK2 Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m3 (NH4)2SO4, at concentrations ranging from012 mol m3. MES at 9 mol m3 and 12 molm3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH4+ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens 相似文献
18.
MACDUFF J. H.; JARVIS S. C.; LARSSON C-M.; OSCARSON P. 《Journal of experimental botany》1993,44(9):1475-1484
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·030.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3] between 10100 mmol m3(RGR=0·15 0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·030·06d1 , but decreased thereafter to a theoretical minimumvalue at RGR 相似文献
19.
Activity of glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate:NADP oxidoreductase, EC 1.1.1.49
[EC]
) preparation from sweet potatoroot tissue was markedly altered in the presence of variousions. Cations or anions were effective in the following order:Na$, K$>Tris$>NH4$>Mg2$>Ca2$, or Cl>NO3,HPO42>SO42>HCO3. Activity was inhibitedat high concentrations of Ca2$, and HCO3,. In an investigationon the dependence of the activity on pH, two activity peakswere clearly observed at low ionic strength. Ionic strength altered both the Km and Vmax for glucose 6-phosphate(G6P). A Lineweaver-Burk plot for the enzyme, with respect toG6P, showed a bimodal nature at low ionic strength; suggestingnegative cooperativity. Deviation from linearity of the plotwas less with an increase in the ionic strength.
1 Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku, Tokyo 113. (Received September 18, 1971; ) 相似文献
20.
Chloride Transport in Chara: I. KINETICS AND CURRENT-VOLTAGE CURVES FOR A PROBABLE PROTON SYMPORT 总被引:3,自引:0,他引:3
Chara cells show an inward positive electric current acrossthe plasmalemma when exposed to Cl under voltage-clampconditions. The rapid rise of this current suggests that itis directly associated with the inward transport of Cl.The dependence of the current on Cl concentration showssaturation, the data fitting the Michaelis-Menten equation withVm up to 100 nmol m2 s1 (for Clstarvedcells) with KM 1020 µM, and with some allowancefor an unstirred layer of water adjacent to the membrane. Theeffects on the current of clamp potential, illumination, withdrawalof alkali metal cations, and addition of amine were also investigated.These results suggest that the mechanism is the symport of 2H+ with each Cl, and that the actions of light, externalK+, and amine in stimulating Cl, influx are indirect. 相似文献