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1.
The activity of plasma membrane H+-ATPase was measured withmembrane fragments of guard-cell protoplasts isolated from Viciafaba L. ATP hydrolytic activity was slightly inhibited by oligomycinand ammonium molybdate, and markedly inhibited by NO3and vanadate. In the presence of oligomycin, ammonium molybdateand NO3, the ATP-hydrolyzing activity was strongly inhibitedby vanadate. It was also inhibited by diethylstilbestrol (DES),p-chloromercuribenzoic acid (PCMB) and Ca2+, but slightly stimulatedby carbonyl cyanide m-chlorophenylhydrazone (CCCP). The acitivityhad higher specificity for ATP as a substrate than other phosphoricesters such as ADP, AMP, GTP and p-nitrophenylphosphate; theKm was 0.5 mM for ATP. The activity required Mg2+ but was notaffected by K+, and it was maximal around pH 6.8. When guard-cellprotoplasts were used instead of membrane fragments, the ATPaseactivity reached up to 800µmol Pi.(mg Chl)1.h1in the presence of lysolecithin. These results indicate thatthe guard cell has a high plasma membrane H+-ATPase activity. (Received December 23, 1986; Accepted April 28, 1987) 相似文献
2.
Proton Transport and pH Control in Sinapis alba Root Hairs: A Study carried out with Double-Barrelled pH Micro-electrodes 总被引:3,自引:0,他引:3
Continuous measurements of cytoplasmic pH (pHc) in Sinapis roothairs have been carried out with double-barrelled pH-micro-electrodesin order to gain information on translocation of protons acrossthe plasmalemma and cytoplasmic pH control. (i) The cytoplasmicpH of Sinapis (733 ? 012, standard conditions)changes no more than 0.1 pHc, per pHo-unit, regardless of whethercyanide is present or not. (ii) Weak acids rapidly acidify pHcand hyperpolarize, while weak bases alkalize pHc and depolarizethe cells, (iii) 1.0 mol M,3 NaCN acidifies the cytoplasm by0.4 to 0.7 pH-units, but alkalizes the vacuole. (iv) 20 mmolm3 CCCP has no significant effect on pHc, if added atpH 9.6 or 7.2, but acidifies pHc by 1.3 units at pH 4.3. Inthe presence of CCCP, cyanide acidifies the cytoplasm, (v) Chloridetransiently acidifies pHc, while K+, Na+, and have no significant effects, (vi) Cytoplasmic buffer capacityforms a bell-shaped curve versus pHc with an optimum of about50 mol m3 H+pHc-unit. The modes of proton re-entry and the effects of active and passiveproton transport on cellular pH control are critically discussed.It is suggested that the proton leak, consisting of H+-cotransport(e.g. H+/Cl) rather than H+-uniport, is no threat topHc. The proton export pump, although itself reacting to changesin pHc, influences pHc only to a minor extent. It is concludedthat buffer capacity and membrane transport play moderate rolesin pHc control in Sinapis, while the interlocked H+-producingand -consuming reactions of cellular metabolism are the mainregulating factors. This makes pH control in Sinapis quite differentfrom bacterial and animal cells. Key words: Cytoplasmic pH, double-barrelled pH micro-electrode, pH control, proton transport, Sinapis 相似文献
3.
Characterization of the vacuolar-type H+-ATPase from guard cell protoplasts of Commelina 总被引:1,自引:0,他引:1
Willmer C.M.; Grammatikopoulos G.; Lascve G.; Vavasseur A. 《Journal of experimental botany》1995,46(4):383-389
Characteristics of the vacuolar-type (V-type) H+-ATPase fromguard cell protoplasts of Commelina communis L. were investigatedusing a linked enzyme assay and nitrate inhibition as a diagnosticindicator of the enzyme activity. ATPase activity was completelyinhibited by about 50 mol m3 nitrate and activity wasoptimal near pH 8.0. The temperature optimum for activity wasabout 37 C and an Arrhenius plot indicated changes in activationenergy for the ATPase at 15C and possibly at about 30 C. Theenzyme was stimulated by Cl while Ca2+ inhibited activity(l50 = 1.5 mol m3). The apparent Km (MgATP) was 0.62mol m3. Incubation of guard cell protoplasts for up to 5 h in 50 µMabscisic acid (ABA) or 25µM fusicoccin (FC) did not affectsubsequent ATPase activity. In vitro assays with FC or ABA alsodid not affect enzyme activity. Activity was not affected bylight or potassium ferricyanide, two factors which are knownto influence stomatal activity. Beticoline was a potent inhibitorof activity (l50 = 50 µM) while DCCD was less effective(l50 = 90µM). On chlorophyll, protein and protoplast bases, V-type ATPaseactivity was greater in guard cell protoplasts than mesophyllcell protoplasts by 66, 13.9 and 1.9, respectively. On atonoplast surface area basis the enzyme activity was 5.6 timeshigher in guard cell protoplasts than in mesophyll cell protoplasts Thus, although the characteristics of the V-type, H +-ATPaseof GCP are very similar to those found in other cell types,rates of activity and probably tonoplast enzyme density aremuch greater in guard cell protoplasts than mesophyll cell protoplastsof C. communis which corresponds with the large and rapid ionfluxes across the tonoplast associated with stomatal movements Key words: Guard cell protoplasts, stomata, V-type H +-ATPase 相似文献
4.
L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake 总被引:1,自引:0,他引:1
The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H+ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The Km values of thethree affinity sites were 1.4 x 103 M, 1.3 x 104M, 4.3 x 105 M; the maximum velocity values were 3.3x 108, 4.5 x 109, 1.8 x 109 mol/10 min/4x 106 cells. (Received April 18, 1981; Accepted August 25, 1981) 相似文献
5.
Guard cell protoplasts (GCP) were prepared from leaves of Commelinacommunis L. and phosphoenolpyruvate carboxylase (PEPc) activityrecorded after injection of the protoplasts directly into theassay medium. The GCP were lysed immediately by the presenceof Triton X-100 and a lowered osmotic concentration in the assaycuvette enabling PEPc activity to be measured with nascentenzyme. There was no light activation of the enzyme with KmPEP (about 3.7 mol m3) and Vmax being similar in light-ordark-treated protoplasts. Illumination of the GCP in the presenceof CO2-free air and KCI, a treatment which is known to swellGCP, did not change the kinetics. PEPc activity at saturating PEP was very sensitive to malateinhibition, 20 mmol m3 (the I50 value) inhibiting activityby about 50%. Inhibition was similar in light- or dark-treatedprotoplasts. Malate inhibition was, however, much less (I50= 500 mmol m3) if the enzyme source was a protoplastextract kept in the absence of glycerol. Inclusion of 20% glycerolin the extraction medium maintained the enzyme in the malate-sensitiveform as occurred in the in vivo assays. The high apparent KmPEP and the high sensitivity to malate inhibition of GCP PEPcare features unlike those observed with PEPc from leaf tissuesof C4 and CAM plants and from GCP extracts. PEPc activity increased slightly in the presence of KCI in theassay medium up to about 10 mol m3 and thereafter activityslowly declined as KCI concentrations increased further. Key words: Guard cell protoplasts, phosphoenolpyruvate carboxylase 相似文献
6.
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
7.
Guard cell protoplasts were isolated enzymatically from theepidermis of Vicia faba L. and their photosynthetic activitieswere investigated. Time courses of light-induced changes inthe chlorophyll a fluorescence intensity of these protoplastsshowed essentially the same induction kinetics as found formesophyll protoplasts of Vicia. The transient change in thefluorescence intensity was affected by DCMU, an inhibitor ofphotosystem II; by phenylmercuric acetate, an inhibitor of ferredoxinand ferredoxin NADP reductase; and by methyl viologen, an acceptorof photosystem I. Low temperature (77 K) emission spectra ofthe protoplasts had peaks at 684 and 735 nm and a shoulder near695 nm. A high O2 uptake (175 µmol mg1 Chl hr1)was observed in guard cell protoplasts kept in darkness, whichwas inhibited by 2 mM KCN or NaN3 by about 60%. On illumination,this O2 uptake was partially or completely suppressed, but itssuppression was removed by DCMU, which indicates that oxygenwas evolved (150 µmol mg1 Chl hr1) photosynthetically.We concluded that both photosystems I and II function in guardcell chloroplasts and that these protoplasts have high respiratoryactivity. (Received January 30, 1982; Accepted May 15, 1982) 相似文献
8.
The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses 总被引:2,自引:1,他引:1
Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO-3) content of root and shoot and NO-3 and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO-3 concentrations (0·120mol m3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m3 NO-3 For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO-3 concentration on the partitioning of NO-3 assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m3 NO-3 and that for all cereals, shoot assimilationincreased in importance as applied NO-3 concentration increasedfrom 1.0 to 20 mol m3 At 5.020 mol m3 NO3,the data indicated that the shoot played an important if notmajor role in NO-3 assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO-3 assimilation at 0.5 mol m3NO-3 but shoot assimilation was predominant at 5.0 mol m3NO-3 Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m3 NO-3 Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap 相似文献
9.
Abscisic Acid-Induced Membrane Potential Changes in Barley Aleurone Protoplasts: a Possible Relevance for the Regulation of rab Gene Expression 总被引:2,自引:0,他引:2
Heimovaara-Dijkstra Sjoukje; van Duijn Bert; Libbenga Kees R.; Heidekamp Freek; Wang Mei 《Plant & cell physiology》1994,35(5):743-750
The effect of ABA on the membrane potential of barley (Hordeumvulgare cv. Himalaya) aleurone protoplasts was studied by measuringthe distribution of the lipophilic cation tetraphenylphosphonium(TPP+). The resting membrane potential (Em) according to ourmeasurements with TPP+ is about 53 mV and is in agreementwith membrane potential values as measured with intracellularmicroelectrodes (about 55 mV). The TPP+-measurementscould demonstrate a clear dependence of the resting Em on theexternal pH (pHe). Stimulation of the protoplasts with ABA induced a transienthyperpolarization of the membrane to 62 mV as measuredwith TPP+. The hyperpolarization was ABA-concentration dependent. Inhibition of the H+-ATPases with the specific proton pump inhibitorsdiethylstilbestrol (DES) or Micanozole effectively preventedhyperpolarization. This indicates that the hyperpolarizationis consistent with the activation of plasma membrane H+-ATPases.The K+-inward rectifier inhibitor BaCl2 was able to prolongthe hyperpolarization. This result suggests that the hyperpolarizationcauses the opening of K+-channels. The ABA-induced proton-pump activation may be involved in ABA-inducedgene-expression, as DES was able to inhibit this gene expression.BaCl2 did only show a slight inhibitory effect on ABA-inducedgene-expression. (Received January 4, 1994; Accepted April 12, 1994) 相似文献
10.
The acidophilic alga Dunaliella acidophila exhibits optimalgrowth at pH 1. We have investigated the regulation of phosphateuptake by this alga using tracer techniques and by performingintracellular phosphate measurements under different growthconditions including phosphate limitation. In batch culturewith 2·2 mol m3 phosphate in the medium the uptakeof phosphate at micromolar phosphate concentrations followeda linear time dependence in the range of minutes and rates werein the range of 1 µmol phosphate mg1 chl h1,only. However, under discontinuous phosphate-limited growthconditions, tracer influx revealed a biphasic pattern at micromolarphosphate concentrations: An initial burst phase resulted ina 104-fold internal phosphate accumulation and levelled offafter about 10 s. A double reciprocal plot of the initial influxrates obtained for phosphate-limited and unlimited algae exhibitedMichaelis-Menten kinetics. Phosphate limitation caused a significantactivation of the maximum velocity of uptake, yielding Vmaxup to 1 mmol mg1 chl h1 as compared to valuesin the order of 50 µmol phosphate mg1 chl h1for the second phase (this magnitude is also representativefor non-limited batch cultures). Concomitantly the Michaelisconstant was altered from 4 mmol m3 to 0·7 mmolm3. The rapid uptake of phosphate was inhibited by arsenateand FCCP and was not stimulated by Na+. The pH dependence oftracer accumulation and measurements of the intracellular phosphatepool under different growth conditions indicate that at lowpH and low external phosphate concentrations the high protongradient present under these conditions is utilized for a H3PO4uptake or a H+/H2PO4 cotransport. However, when the externalphosphate concentration was increased to levels sufficientlyhigh for transport to be driven by the positive membrane potential(10 mol m3 phosphate), the pH dependence of phosphateuptake was more complex, but could be explained by the uptakeof H3PO4 or a H+/H2PO4-cotransport at low pH and a differenttype H2PO4-transport (with unknown type of ion coupling)at high pH-values. It is suggested that this flexible couplingof phosphate transport is of essential importance for the acidresistance of Dunaliella acidophila. Key words: Acid resistance, Dunaliella acidophila, phosphate cotransport, phosphate limitation, plasma membrane, sodium 相似文献
11.
Salinity-induced Malate Accumulation in Chara 总被引:3,自引:0,他引:3
Ion absorption by Chara corallina from solutions containingpredominantly KC1 or RbCl at up to 100 mol m3 resultedin accumulation of salts and turgor regulation. Turgor regulationdid not occur in solutions containing Na+ or Li+salts. Duringion absorption from various salts of K+ and Rb+ vacuolar cationconcentration exceeded Cl concentration. This differencewas shown to be balanced by the synthesis and accumulation ofmalate. Vacuolar malate concentration reached 48 mol m3,with accumulation occurring at rates of up to 0.45 mol m3h1. Malate accumulation was inhibited by low externalpH and was dependent upon external HCO3 concentration.The synthesis of malic acid and its subsequent dissociationimposed a severe acid load on the cell. Biophysical regulationof cellular pH was achieved by a H+efflux at a rate of about40 nmol m2 s1from the cell. The results presentedargue against cytoplasmic Cl, HCO3 or pH regulatingmalate accumulation in Chara and it is suggested that malatetransport across the tonoplast may regulate malate accumulation. Key words: Malate, Chara corallina, pH regulation, salinity 相似文献
12.
DNA polymerases were purified several hundred-fold from the10 000 x g soluble (polymerase I) and particulate (polymeraseIII) fractions prepared from virus PBCV-1 infected ChlorellaNC64A extracts. Both DNA polymerases exhibited optimal activitywith activated calf thymus DNA at pH 8.5. DNA polymerase I required3.0 mol m3 MgSO4 and 150 to 250 mol m3 KCl foroptimum activity whereas, DNA polymerase III required 2.0 molm3 MgSO4 and 150 mol m3 KCl. Both enzymes wereinhibited by pyrophosphate, actinomycin D, ethidium bromide,dideoxythymidine triphosphate, and N-ethylmaleimide but wererelatively insensitive to aphidicolin. DNA polymerase I differedfrom DNA polymerase III in its response to cations (particularlyNH4Cl), elution from a DEAE cellulose column, and molecularweight. Key words: Algal virus, DNA polymerase, Chlorella 相似文献
13.
Takeda Junko; Abe Shunnosuke; Morikawa Hiromichi; Senda Mitsugi 《Plant & cell physiology》1983,24(4):667-676
The electrophysiological properties of the membrane of Nicotianatabacum var. Sarnsun cultured cells were determined using amicroelectrode technique in standard medium containing 1 mMKC1, 1 mM NaCl and 1 mu CaCl2 at pH 7. Tobacco callus was derivedfrom the pith (Em=104.4%16.2 mV). The membrane potentialsof the callus cells did not show a symmetrical Gaussian distributionbut were scattered over a wide range. The percentage of highmembrane potential cells increased as the subculture was continueduntil about 11 months and then decreased. The response of themembrane potential to electric stimulus, ionic composition,metabolic inhibitors, sugars and amino acids was characteristicof high (Em={small tilde}160 220 mV; H-cells)and low (Em=80{small tilde}90 mV; L-cells) membranepotential cells. The membrane potential of H-cells was largelydepolarized by addition of CN, carbonium cyanide m-chlorophenylhydrazone,decyclohexylcarbodiimide, and triphenyltin chloride and transientlydepolarized by addition of glucose, galactose, mannose or sucrose,and D-alanine, L-alanine or Llysine, but the membrane potentialof L-cells was not. (Received December 3, 1982; Accepted March 16, 1983) 相似文献
14.
The relationships between CO2 concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO2 supply around the roots. Free CO2 in sediment-interstitial-waterranged from 101 mol m3 (Esthwaite), 0.79 mol m3(peat), 0.32 mol m3 (silt) and 017 mol m3(sand), with plants maintained under PAR of 40 µmol m2s1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO2 had larger leaf fresh weight (069 g) andtotal surface area (223 cm2 g1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm2g1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO2 concentration[CO2], was highest in the sand-grown plants (269 molm3, corresponding to 6.5% CO2 in air) and lowest inthe Esthwaite plants (108 mol m3). Expressionof CAM in transplants was also greatest in the low CO2 regime,with H+ (measured as dawn-dusk titratable acidity) of 50µmolg fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO2]1 and would makea major contribution to daytime CO2 fixation in vivo. A range of leaf sections (02, 10, 50 and170 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO2 evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO2 and 10mol m3 exogenous CO2 was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O2 g1 fr. wt. h1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO2 g1 fr. wt. h1) with a K0.5 of 80 mmol m3.In terms of light response, saturation of photosynthesis intissue slices occurred at 8501000 µmol m2s1 although light compensation points (611 µmolm2s1) and chlorophyll a: b ratios (1.3) were low.While CO2 and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO2 supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO2 concentrating mechanisms interact inintact plants to maintain saturating CO2 levels within leaflacunae, although the responses of the various components ofCO2 supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO2 concentration, crassulacean acid metabolism, root inorganic carbon supply, CO2 concentrating mechanism 相似文献
15.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
16.
TREBACZ KAZIMIERZ; FENSOM D. S.; HARRIS ANDREW; ZAWADZKI TADEUSZ 《Journal of experimental botany》1988,39(11):1561-1573
Using NaH 14CO3 (0.1 to 3.0 mol m 3) fed to 5.0 mm ofan internodal cell of Nitella flexilis in artificial pond waterat pH 6.8 and 1925 °C, we have found that the carbohydrates(lactose, xylose, mannose, galactoseand sucrose) are formedby photo-assimilation from 14C-DIC (dissolved organic carbon)in 1 h and are carried in the cytoplasm with amino acids (glutamineand alanine in particular) to the node attached to a tandeminternodal cell. These small sacchandes and some amino acidspassed, apparently unchanged, across the node into the sinkcell. Influx of DIC was highly sensitive to inhibitors of photosystemsI and II (at concentrations around 1.0 mol m3) and touncouplers of phosphorylation. Most influx inhibitors, exceptfor NaN3, also reduced % transnodal transport. NH4+ (1.0 to5.0 mol m3) appeared to reduce % transport in light (butnot in dark) with much less effect on influx. Dinitrophenoland Na citrate (at pH 8.2) also strongly reduced apparent %transport without altering cytoplasmic streaming rates. Someof the apparent reduction of transport could be due to an alterationof metabolism or of sequestering in the feed cell, but withNH4+ the latter was not detectable. Our findings support thehypothesis that transnodal transport, including that via theplasmodesmata, is at least partly active and requiresmetabolic energy to sustain it. Key words: Inhibitors, influx, plasmodesmata, nodal transport, 14C, 36Cl 相似文献
17.
Calcium Inhibits Ion-Stimulated Stomatal Opening in Epidermal Strips of Commelina communis L. 总被引:2,自引:0,他引:2
Inoue, H. and Katoh, Y. 1987. Calcium inhibitsion-stimulatedstomatal opening in epidermal strips of Commelina communis L.J.exp. Bot. 38: 142149. Ca2+ suppressed both the ion-stimulated stomatal opening andH+ extrusion of pre-illuminated epidermal strips isolated fromCommelina communis L. In the absence of Ca2+, the rate of H+release was 18 nmol H+ cm2 h1 per epidermal stripunit area in 150 mol m3 KCL at pH 7?4. Half-maximum inhibitionof stomatal opening was observed with 220 mmol m3 ofCa2+. The hexavalent dye, ruthenium red, showed concentration-dependentprevention of the inhibition by Ca2+ of the ion-stimulated stomatalopening. The effect of ruthenium red was non-competitive, andthe K1 for the calcium inhibition was found to be 3?6 mmol m3.The calcium inhibition of H+ extrusion was also prevented byruthenium red. These results suggest that Ca2+ inhibits theactivity of electrogenic H+ translocating ATPase of the guardcell plasma membrane and leads to the suppression of stomatalopening. Key words: Calcium, Commelina communis, ruthenium red, stomata 相似文献
18.
Regulation of Pyruvate Decarboxylase In Vitro and In Vivo 总被引:2,自引:0,他引:2
Results presented in this paper strongly support the view thatregulation of the key enzyme of alcoholic fermentation, pyruvatedecarboxylase (PDC), is achieved in a number of ways, all associatedwith possible lowering of the cytoplasmic pH during anoxia.These mechanisms include not only the well-known acid pH optimumof PDC, but also long-term, reversible changes in characteristicsof the enzyme established both in vitro and in vivo. Following transfer of desalted extracts from pH 6.0 to 7.4,maximal activity of PDC was decreased, while there was a considerableincrease in the lag before maximal activity was reached. Similarchanges in enzyme characteristics were observed when wheat (Triticumaestivum L. cv. Gamenya) roots and rice (Oryza sativa L. cv.Calrose) coleoptiles were transferred from anoxic to aerobicsolutions, provided PDC was assayed within 10 min of the startof maceration. All of the above changes were usually readilyreversible when extracts were returned to pH 6.0, or when plantswere returned to anoxic solutions. Additional regulation of PDC would be achieved by the S0.5 forpyruvate which is 0.75 mol m3 at pH 6.0, 1.0 mol m3at pH 6.8, and 2.5 mol m3 at pH 7.4; the latter is wellabove estimates for pyruvate concentrations in the cytoplasmof aerated tissues. We assess that the combined effects of the acid pH optimum,the high S0.5 at pH 7.4 and the long-term decreases in activityobserved during incubation at pH 7.4 would reduce PDC activityin aerobic cells to at most 7% of the activity in anoxic cells.Possible additional controls for the pathway of alcoholic fermentationare briefly considered. Key words: PDC, regulation, anoxia 相似文献
19.
Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.) 总被引:2,自引:0,他引:2
Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m1 (34.2 mol m3 NaCl)and nodulation was completely inhibited at 7 dS m1 (61.6mol m3 NaCl); the plants died at 8 dS m1 (71.8mol m3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 14 dS m1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N2 fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N2 fixation, Rhizobium, salinity 相似文献
20.
With the use of voltage clamp and current clamp techniques thesupposition was proved that during the hyperpolarizing response(HR) N. obtusa cells generate active electromotive force (emf)at the expense of metabolic energy. Threshold inward currentsent through the plasmalemma of the cell which was depolarizedwith 100 mol m3 KG resulted in the HR with the transferof the membrane's excitable units from the high-conductive stateto the low-conductive state. During the HR the membrane potentialVm increased from 135±10 mV to 290±15mV, the membrane resistance increased from 3.3±1.5 kOhmcm2 to 5.8±1.2 kOhm cm2 and the membrane emf Em increasedfrom 20±4 mV to 93± 15 mV. Changesin the external concentration of K, Na+, Cl andH did not affect the patterns of HR. Cells which weredepolarized by light also generated HR (in normal medium) whichwas accompanied with the increase of Vm, Rm and Em. The highvalue of Em generated during the HR can be explained only withthe involvement of active electrogenic charge transfer acrossthe membrane. 0.05 mol m3 DCCD added to the externalmedium inhibited the HR in both cases. Key words: Active ion transport, Hyperpolarizing response, Nitellopsis obtusa 相似文献