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1.
Reaction of Reconstituted Acceptor Quinone and Dynamic Equilibration of Electron Transfer in the Photosystem I Reaction Center 总被引:1,自引:0,他引:1
Electron transfer mechanism in the spinach photosystem I reactioncenter that contains artificial quinones in place of phylloquinone(2-methyl-3-phytyl-1,4-naphthoquinone, vitamin K1) as the secondaryelectron acceptor, Qø (or A1) was discussed. (1) Mostof the reconstituted quinones oxidized the primary acceptorchlorophyll a, A0, at a rate rapid enough to compete againstthe charge recombination between A0 and the oxidizeddonor chlorophyll P700+. (2) The pathway of electron transferfrom the semiquinone varied depending on the redox potentialvalue of each semiquinone /quinone couple. Low potentialquinones reduced the tertiary acceptor iron-sulfur center, Fx,while the high potential ones reduced P700+ directly with a200-µs halftime. (3) The Em value of each semiquinone/quinone couple in situ in the reaction center was estimatedto be shifted by about 0.3 volt to the negative side from theirhalf wave redox potential values that were measured polarographicallyin dimethylformamide. The shift seems to represent the acceptorproperty of the protein environment at the Qø site. (4)The Em of reconstituted phylloquinone was estimated to be 5080mV more negative than that of Fx. (5) The mechanism of efficientelectron transfer in the reaction center was discussed basedon the dynamic equilibria between the electron transfer componentsand on the estimated Em values. (Received April 9, 1994; Accepted July 7, 1994) 相似文献
2.
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
3.
Imaizumi Nobuyuki; Usuda Hideaki; Nakamoto Hitoshi; Ishihara Kuni 《Plant & cell physiology》1990,31(6):835-844
Photosynthesis is known to occur in rice panicles, but littlehas been reported about the photosynthetic or biochemical characteristicsof such panicles. The estimated gross amount of photo-syntheticallyassimilated CO2 in a panicle is 30% of that in a flag leaf.This result and the good light-intercepting characteristicsof the panicle in the canopy suggest that photosynthesis inthe panicle may contribute significantly to grain filling. Therice panicle is composed of spikelets and of rachis-branchesincluding rachis which have estimated gross rates of photosynthesisduring the 30-day period after anthesis of 130 to 180 and 50to 100 µmol CO2.(mg Chl)1.h1, respectively.The corresponding rate for the flag leaf is 180 to 230 µmolCO2.(mg Chl).h. On the basis of Chl, spikeletshave a high photosynthetic capability which is similar to thatof the flag leaf. The activities of ribulose-l,5-bisphosphate carboxylase (RuBPCase),phosphoenolpyruvate carboxylase (PEPCase), and pyruvate.Pi dikinase(PPDK) in spikelets were 129, 220, and 87 µmol.(mg Chl).h,respectively. The activities of PEPCase and PPDK in spikeletswere considerably higher than those in the flag leaf or rachis-branches.Oxygen-insensitive photosynthesis was found only in spikelets.The Km of NaHCO3 for photosynthesis by slices of spikelets inan aqueous solution (0.6 mM) was considerably lower than thatfor slices of flag leaf (4.2 mM). All these results indicatethat spikelets have different photosynthetic characteristicsfrom those of the flag leaf and rachis-branches. The possibilityof C3C4 intermediate photosynthesis or C4-like photosynthesisin spikelets is discussed.
4Present address: Department of Biochemistry, Faculty of Science,Saitama University, Urawa, 338 Japan (Received February 14, 1990; Accepted June 12, 1990) 相似文献
4.
Oh-oka Hirozo; Kakutani Saki; Matsubara Hiroshi; Malkin Richard; Itoh Shigeru 《Plant & cell physiology》1993,34(1):93-101
The photoactive reaction center (RC) complex from the greensulfur bacterium Chlorobium limicola f. thiosulfatophilum, strainLarsen, was isolated after solubilization and ammonium sulfatefractionation followed by ion-exchange chromatography. The spectrumof the complex was almost identical with that of the similarRC complex isolated by Feiler et al. [(1992) Biochemistry 31:26082614] except for the presence of cytochrome c551instead of c553 in the latter study. A molecular ratio of BChla to P840 of the isolated RC complex was assayed to be 2535.SDSPAGE analysis revealed that the isolated complex containedthree major polypeptides with apparent molecular masses of 68,41 and 21 kDa, respectively. The 21-kDa polypeptide was identifiedto be a heme-binding protein by staining the gel for peroxidaseactivity. The cytochrome c551 was oxidized by flash light ina biphasic manner with half times of 90 and 390 µs, respectively,that coincided with the reduction half times of P840+. Threedistinct iron-sulfur centers assigned to FA, FB and Fx, respectively,from their g-values were detected by EPR spectroscopy at cryogenictemperature. These results suggest that the present preparationcontains a minimal functional unit of the RC of this bacterium,and that this complex appears to lie on a evolutionary linebetween RC's of purple bacteria and photosystem I. (Received August 18, 1992; Accepted October 28, 1992) 相似文献
5.
Yin X Denton J Yan X Strange K 《American journal of physiology. Cell physiology》2007,292(1):C269-C277
An inwardly rectifying swelling- and meiotic cell cycle-regulated anion current carried by the ClC channel splice variant CLH-3b dominates the whole cell conductance of the Caenorhabditis elegans oocyte. Oocytes also express a novel outwardly rectifying anion current termed ICl,OR. We recently identified a worm strain carrying a null allele of the clh-3 gene and utilized oocytes from these animals to characterize ICl,OR biophysical properties. The ICl,OR channel is strongly voltage dependent. Outward rectification is due to voltage-dependent current activation at depolarized voltages and rapid inactivation at voltages more hyperpolarized than approximately +20 mV. Apparent channel open probability is zero at voltages less than +20 mV. The channel has a 4:1 selectivity for Cl over Na+ and an anion selectivity sequence of SCN > I > Br > Cl > F. ICl,OR is relatively insensitive to most conventional anion channel inhibitors including DIDS, 4,4'-dinitrostilbene-2,2'-disulfonic acid, 9-anthracenecarboxylic acid, and 5-nitro-2-(3-phenylpropylamino)benzoic acid. However, the current is rapidly inhibited by niflumic acid, metal cations including Gd3+, Cd2+, and Zn2+, and bath acidification. The combined biophysical properties of ICl,OR are distinct from those of other anion currents that have been described. During oocyte meiotic maturation, ICl,OR activity is rapidly downregulated, suggesting that the channel may play a role in oocyte Cl homeostasis, development, cell cycle control, and/or ovulation. chloride channel; ovulation; cell cycle; meiotic maturation 相似文献
6.
Effects of cytoplasmic Ca2+ on the electrical properties ofthe plasma membrane were investigated in tonoplast-free cellsof Chara australis that had been internally perfused with media,containing either 1 mM ATP to fuel the electrogenic pump orhexokinase and glucose to deplete the ATP and stop the pump. In the presence of ATP, cytoplasmic Ca2+ up to 2.5?105M did not affect the membrane potential (about -190 mV), butmembrane resistance decreased uniformly with increasing [Ca2+]i.In the absence of ATP, the membrane potential, which was onlyabout -110 mV, was depolarized further by raising [Ca2+]i from1.4?106 to 2.5?105 M. Membrane resistance, whichwas nearly the twofold that of ATP-provided cells, decreasedmarkedly with an increase in [Ca2+]i from zero to 1.38?106M, but showed no change for further increases. Internodal cellsof Nitellopsis obtusa were more sensitive to intracellular Ca2+with respect to membrane potential than were those of Charaaustralis, reconfirming the results obtained by Mimura and Tazawa(1983). The effect of cytoplasmic Ca2+ on the ATP-dependent H+ effluxwas measured. No marked difference in H+ effluxes was detectedbetween zero and 2.5?105 M [Ca2+]i; but, at 104M the ATP-dependent H+ efflux was almost zero. Ca2+ efflux experimentswere done to investigate dependencies on [Ca2+]i and [ATP]i.The efflux was about 1 pmol cm2 s1 at all [Ca2+]iconcentrations tested (1.38?106, 2.5?105, 104M).This value is much higher than the influx reported by Hayamaet al. (1979), and this efflux was independent of [ATP]i. Thepossibility of a Ca2+-extruding pump is discussed.
1 Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, 5300 Bonn, F.R.G. (Received September 22, 1984; Accepted February 19, 1985) 相似文献
7.
Involvement of anion channel(s) in the modulation of the transient outward K(+) channel in rat ventricular myocytes 总被引:5,自引:0,他引:5
Lai XG Yang J Zhou SS Zhu J Li GR Wong TM 《American journal of physiology. Cell physiology》2004,287(1):C163-C170
The cardiac Ca2+-independent transient outward K+ current (Ito), a major repolarizing ionic current, is markedly affected by Cl substitution and anion channel blockers. We reexplored the mechanism of the action of anions on Ito by using whole cell patch-clamp in single isolated rat cardiac ventricular myocytes. The transient outward current was sensitive to blockade by 4-aminopyridine (4-AP) and was abolished by Cs+ substitution for intracellular K+. Replacement of most of the extracellular Cl with less permeant anions, aspartate (Asp) and glutamate (Glu), markedly suppressed the current. Removal of external Na+ or stabilization of F-actin with phalloidin did not significantly affect the inhibitory action of less permeant anions on Ito. In contrast, the permeant Cl substitute Br did not markedly affect the current, whereas F substitution for Cl induced a slight inhibition. The Ito elicited during Br substitution for Cl was also sensitive to blockade by 4-AP. The ability of Cl substitutes to induce rightward shifts of the steady-state inactivation curve of Ito was in the following sequence: NO3 > Cl Br > gluconate > Glu > Asp. Depolymerization of actin filaments with cytochalasin D (CytD) induced an effect on the steady-state inactivation of Ito similar to that of less permeant anions. Fluorescent phalloidin staining experiments revealed that CytD-pretreatment significantly decreased the intensity of FITC-phalloidin staining of F-actin, whereas Asp substitution for Cl was without significant effect on the intensity. These results suggest that the Ito channel is modulated by anion channel(s), in which the actin cytoskeleton may be implicated. transient outward potassium current; anion channel; actin cytoskeleton; myocyte; potassium ion 相似文献
8.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献
9.
The effects of UV radiation on the low temperature fluorescenceand primary photochemistry of PSII and PSI of spinach chloroplastswere studied. Fluorescence induction curves at 196°Cwere measured at 695 nm for PSII fluorescence and at 730 nmfor PSI fluorescence to determine both the initial Fo and finalFM levels. The primary photochemistry of PSII was measured asthe rate of photoreduction of C-550 at 196°C, thatof PSI as the rate of photooxidation of P700 at 196°C.The results were analyzed in terms of a model for the photosyntheticapparatus which accounts for the yields of fluorescence andprimary photochemistry. According to this analysis UV radiationincreases nonradiative decay processes at the reaction centerchlorophyll of PSII. However, the effect of UV radiation isnot uniform throughout the sample during irradiation so thataccount must be taken of the fraction of PSII reaction centerswhich have been irradiated at any given time. UV radiation alsoinactivates P700 and causes a slight increase in nonradiativedecay in the antenna chlorophyll of PSI. All fluorescence ofvariable yield, FV = FMFo, at 730 nm is due to energytransfer from PSII to PSI so that the sensitivity of Fv to UVradiation is the same at 730 and 695 nm.
1Present address: Department of Biology, Faculty of Science,Toho University, Narashino, Chiba 275, Japan.
2Present address: Central Research Laboratories, Fuji PhotoFilm Co., Ltd., 105 Mizonuma, Asaka-Shi, Saitama 351, Japan. (Received September 10, 1975; ) 相似文献
10.
The effects of phthalate esters on chlorophyll a2 fluorescencein radish plants (Raphanus sativus L. cv. Cherry Belle) wereexamined Fluorescence yield was increased in those plants exposedto an aerial concentration of 120 ng dm3 dibutyl phthaiatc(DBP) at a rate of 3.0 dm3 min1 for 13 d. Comparisonof fluorescence enhancement ratios and Fred/Fox, suggests thatDBP inhibits photosynthesis in radish plants at a site afterQA. Both DBP and diisobutyl phthalate (DIBP) strongly inhibiteduncoupled (PS2+PS1) electron transport rates in thylakoids isolatedfrom spinach. At a chlorophyll concentration of 10 µgcm3 the concentrations of DBP and DIBP exhibiting 50%inhibition were 44 mmol m3 and 42 mmol m3 respectively.Basal electron transport rates were also inhibited, with 87mmol m3 of DBP or DIBP producing 50% inhibition. Measurementof photosystcm 1 activity suggested that the main site of actionof these phthalates was localized at a site near the reducingside of photosystem 2. Key words: Phthalate, plasticiser, chlorophyll, fluorescence, photosynthesis, inhibition 相似文献
11.
Nakayama Ishizue; Kamiya Yuji; Kobayashi Masatomo; Abe Hiroshi; Sakurai Akira 《Plant & cell physiology》1990,31(8):1183-1190
Inhibition of the biosynthesis of gibberellins by prohexadione,3,5-dioxo-4-propionylcyclo-hexanecarboxylic acid, was studiedwith cell-free systems derived from immature seeds of Cucur-bitamaxima, Phaseolus vulgaris and Pisum sativum. Prohexadione,at a concentration of 104 M, inhibited C-7 oxidationof GA12-aldehyde, C-20 oxidation of GA15, conversion of C20-gib-berellinsto C19-gibberellins, 3ß-hydroxylation, 2,3-dehydrogenationof GA20, 2,3-epoxidation of GA5 and 2ß-hydroxylationof GA9 and GA20. The 3ß-hydroxylase activity appearedto be more sensitive to prohexadione than were the C-20 oxygenaseand the 2ß-hydroxylase activities. The conversionof mevalonic acid to GA12-aldehyde and the 13-hydroxylationof GA12 were not affected by prohexadione at a concentrationof 3 ? 104 M. All of the steps inhibited by prohexadioneare oxidation steps catalyzed by soluble enzymes that require2-oxoglutarate, Fe2+ and oxygen, and all of them occur distalto the synthesis of GA12-aldehyde in the biosynthesis of gibberellins. (Received April 4, 1990; Accepted September 14, 1990) 相似文献
12.
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
13.
K+ efflux from tobacco (Nicotiana tabacum L, cv. Samsun NN)leaf discs into the external medium was increased and the membranepotential (Em) changed in the positive direction with a changein pH from 8.0 to 4.0. Em was affected by the external concentrationof KCl, greatly decreasing with a change in concentration from1 mM to 100 mM. The equilibrium potential of the membrane forK+ (Ek) was decreased in a Nernst fashion with increasing externalconcentrations of KCl. Ek is more positive than Em above ca.50 µM KCl. Most of the experiments were carried out underconditions in which the difference between the electrochemicalpotential for K+ on the inside to the outside of the cell (µkis positive. Thus, K+ may passively flow to the outside of thecells accompanied by the depolarization of the membrane. Abscisic acid (ABA) increased the K+ efflux under conditionsof passive transport. K+ efflux was accelerated with an increasingconcentration of ABA, being maximal at 104 M103M. This acceleration was due to the enhancement of the potassiummotive force (µk/F) which is the force causing the netpassive transport of K+. The membrane potential was decreasedfrom 205 mV to 170 mV by 2 x 104 M ABAwithin 10 min. The depolarization was not transient, being lostfor at least 3 hr. These results show that ABA accelerated passive K+ efflux, whichaccompanied depolarization of the membrane. (Received June 22, 1981; Accepted August 24, 1981) 相似文献
14.
Ammonium Nutrition in Ricinus communis: Its Effect on Plant Growth and the Chemical Composition of the Whole Plant, Xylem and Phloem Saps 总被引:2,自引:0,他引:2
Allen, S. and Smith, J A. C. 1986. Ammonium nutrition in Ricinuscommunis: its effect on plantgrowth and the chemical compositionof the whole plant, xylem and phloem saps.J. exp. Bot.37: 15991610. The growth and chemical composition of Ricinus communis cultivatedhydroponically on 12 mol m 3 NO3-N were comparedwith plants raised on a range of NH4+-N concentrations. At NH4+-Nconcentrations between 0·5 and 4·0 mol m3,fresh- and dry-weight yields of 62-d-old plants were not significantlydifferent from those of the NO3-N controls. Growth wasreduced at 0·2 mol m3 NH4+-N and was associatedwith increased root. shoot and C: organic N ratios, suggestingthat the plants were N-limited. At 8·0 mol m3NH4+-N, growth was greatly restricted and the plants exhibitedsymptoms of severe NH4+ toxicity. Plants growingon NH4+-N showed marked acidification of the rooting medium,this effect being greatest on media supporting the highest growthrates. Shoot carboxylate content per unit dry weight was lower at mostNH4+-N concentrations than in the NO3-N controls, althoughit increased at the lowest NH4+-N levels. Root carboxylate contentwas comparable on the two N sources, but also increased substantiallyat the lowest NH4+-N levels. N source had little effect on inorganic-cationcontent at the whole-plant level, while NO3 and carboxylatewere replaced by Cl as the dominant anion in the NH4+-N plants.This was reflected in the ionic composition of the xylem andleaf-cell saps, the latter containing about 100 mol m3Cl in plants on 8·0 mol m3 NH4+. Xylem-saporganic-N concentration increased more than threefold with NH4+-N(with glutamine being the dominant compound irrespective ofN source) while in leaf-cell sap it increased more than 12-foldon NH4+-N media (with arginine becoming the dominant species).In the phloem, N source had little or no effect on inorganic-cation,sucrose or organic-N concentrations or sap pH, but sap fromNH4+-N plants contained high levels of Cl and serine. Collectively, the results suggested that the toxic effects ofhigh NH4+ concentrations were not the result of medium acidification,reduced inorganic-cation or carboxylate levels, or restrictedcarbohydrate availability, as is commonly supposed. Rather,NH4+ toxicity in R. communis is probably the result of changesin protein N turnover and impairment of the photorespiratoryN cycle. Key words: Ricinus, ammonium nutrition, nitrate, whole-plant composition, xylem, Phloem, amino acids, carboxylate 相似文献
15.
Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day1 and 630 mg.day1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO2.g totalbody mass1.h1 at 15°C, when the snails wereactive, and 11.27 µlO2.g total body mass1.h1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990) 相似文献
16.
Treatment of S-sufficient or S-deficient Chlorella pyrenoidosacells with NaHSO3, during an 8-h period in the light, significantlydecreased their chlorophyll and dry matter contents when thecells were incubated in the presence or absence of SO42+. Incontrols lacking HSO3, when the starting pH was 7.5,dry matter and chlorophyll contents increased slightly, whereasno significant changes in either occurred at a starting pH of3.0 when the cells and medium contained SO4. In the dark,at both pH 3.0 and 7.5, dry matter and chlorophyll contentsdecreased slightly. Bisulphite treatment in the dark causedlittle decrease of either dry matter or chlorophyll when cellsand medium contained SO42. However, in its absence, drymatter decreased markedly, but there was little change of chlorophyllcontent in the dark. The interactions between HSO3 asa source of S and as an inhibitor of growth and chlorophyllformation are discussed in the context of the changes inducedby light and alternative sources of S. Overall, the harmfuleffects of HSO3 outweigh any role it has as a sourceof S, since its effects are ameliorated by SO42. 相似文献
17.
Ritchie Raymond J.; Trautman Donelle A.; Larkum A.W.D. 《Plant & cell physiology》1997,38(11):1232-1241
Phosphate uptake rates in Synechococcus R-2 in BG-11 media (anitrate-based medium, not phosphate limited) were measured usingcells grown semi-continuously and in continuous culture. Netuptake of phosphate is proportional to external concentration.Growing cells at pHo 10 have a net uptake rate of about 600pmol m2 s1 phosphate, but the isotopic flux for32P phosphate was about 4 nmol m2 s1. There appearsto be a constitutive over-capacity for phosphate uptake. TheKm and Vmax, of the saturable component were not significantlydifferent at pHo 7.5 and 10, hence the transport system probablyrecognizes both H2PO4and HPO24. The intracellularinorganic phosphate concentration is about 3 to 10 mol m3,but there is an intracellular polyphosphate store of about 400mol m3. Intracellular inorganic phosphate is 25 to 50kJ mol1 from electrochemical equilibrium in both thelight and dark and at pHo 7.5 and 10. Phosphate uptake is veryslow in the dark ( 100 pmol m2 s1) and is light-activated(pHo 7.51.3 nmol m2 s1, pHo 10600 pmol m2s1). Uptake has an irreversible requirement for Mg2+in the medium. Uptake in the light is strongly Na+-dependent.Phosphate uptake was negatively electrogenic (net negative chargetaken up when transporting phosphate) at pHo 7.5, but positivelyelectrogenic at pHo 10. This seems to exclude a sodium motiveforce driven mechanism. An ATP-driven phosphate uptake mechanismneeds to have a stoichiometry of one phosphate taken up perATP (1 PO4 in/ATP) to be thermodynamically possible under allthe conditions tested in the present study. (Received June 16, 1997; Accepted September 4, 1997) 相似文献
18.
Phototransformation of the red-light-absorbing form (PR) tothe far-red-light-absorbing form (PFR) of phytochrome in 7-day-oldetiolated pea epicotyl hook segments was examined at 0.5C aftera red laser flash excitation using a multichannel transientspectra analyser with electrically gated photomultiplier. Effectsof a red laser pulse on the induction of phototransformationfrom PR to PFR were saturated at Ca. 15 mJ for flash wavelengthsof both 640 and 655 nm. The amount of PFR induced by a saturatinglaser pulse was ca. 50% of that obtained at the photostationaryequilibrium. A difference spectrum measured 15 µs afterthe flash showed an absorbance increase at 697 nm and a decreaseat 663 nm. A difference spectrum determined 200 ms after theflash showed no such major absorbance increase. Kinetic analysisof the rapid absorbance decrease at 700 and 710 nm gave onesimple first-order reaction component having a rate constantof 2,500 s1. Kinetics of PFR appearance measured by absorbanceincrease at 750 nm was resolved into three first-order reactionshaving rate constants of 5, 1.8 and 0.4 s1. The secondflash light of 710 nm given 2 µs and 2 ms after the firstred flash irradiation on PR resulted in the formation of PRrather than PFR. (Received February 8, 1985; Accepted April 11, 1985) 相似文献
19.
In vitro culture of Picea sitchensis (Bong.) Carr. needle explantson a number of basal culture media indicated that a complexmixture of organic additives was neither essential nor stimulatory.Adventitious bud production occurred at inorganic nitrogen levelsof 1560 x 103M and 7.530 x 103 Min the adventitious bud induction and elongation media, respectively,when a well-balanced ratio of NH4+:NO3 was maintained.However, necrosis was increased at the highest level of inorganicnitrogen. Organogenesis was more sensitive to changes in theratio of NH4+:NO3. Complete replacement of NH4+ withNO3 during the adventitious bud induction passage severelyinhibited organogenesis, indicating that a reduced form of nitrogenmay be essential for adventitious bud differentiation. Conversely,a high proportion of NH4+ in either the adventitious bud inductionor elongation medium increased tissue necrosis and inhibitedbud induction, reflecting the potential toxicity of this ion.Explants from different individual trees were found to varyconsiderably in their morphogenetic responses, but NH4+:NO3ratios of 1:5 or 1:2 were o ptimal for all individual treeswhich developed adventitious buds from needle cultures. Picea sitchensis, Sitka spruce, tissue culture, nitrogen 相似文献
20.
Variable fluorescence (Fv) of intact leaves was measured whenthe temperature was lowered at a rate of 12?C per mn,from 20?C to 20?C. The quantum flux density of the excitinglight was 12 µE m2 sec1 in orderto sensitize F only at 20?C. The fluorescence yield decreasedrapidly at the freezing point of the leaf and upon further coolingthe fluorescence yield increased again. Fm was obtained a fewdegrees below the freezing point. Repeated freeze-thaw cycles caused successively increased damageto the thylakoid membranes on either the oxidizing or the reducingside of photosystem II. An eventual loss of Fv over Fo was typicalfor damage on the water splitting side of photosystem II, whereasdamage after the primary electron acceptor Q of photosystemII was characterized by an invariable fluorescence yield atFm over the temperature range examined. (Received January 18, 1982; Accepted June 12, 1982) 相似文献