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1.
A Comparison between the Uptake of Potassium by Plants from Solutions of Constant Potassium Concentration and during Depletion 总被引:6,自引:0,他引:6
A comparison was made between two methods of measuring the relationshipbetween the external [K+] and the flux of K+ into whole plantsof Lolium perenne and Raphanus sativus. The values of flux obtainedfrom solutions of 1.2 µM K+ held constant around the rootswere three and six times greater for Lolium and Raphanus respectivelythan the values obtained at the same concentration in a depletionexperiment in which the solutions, initially 100 µM K+,were depleted to below 1.2 µM K+ by plant uptake. In thedepletion experiment with Lolium, the flux was higher into plantsgrown at low [K+] than into plants grown at 100 µM eventhough [K+] within the plant was about the same for all groupsof plants. It is suggested that Lolium grown at low [K+] hasan efficient mechanism for K+ uptake which continues to operatefor some time after the plants have been transferred to a higherconcentration. With both species, Km was 1520 µMin the depletion experiment and below 1 µM when concentrationswere held constant. 相似文献
2.
The uptake of K+ by plant roots is matched to the demand forK+ for growth. The growing shoot must communicate its K+ requirementto the root. It has been suggested that this might be effectedby varying the amount of K+ retranslocated from the shoot tothe root via the phloem. It is predicted that less K+ is returnedto the roots in K+-deficient plants and that this promotes compensatoryK+ uptake from the external medium. These experiments addressthis hypothesis. Rye (Secale cereale L.) was grown hydroponically in completenutrient solutions containing either 100 aM or 400 µMK+. Plant development, shoot fresh weight (FW) and plant drymatter accumulation did not differ between seedlings grown atthese K+ concentrations. However, root FW was lower in seedlingsgrown in solutions containing 100 µM K+, which resultedin a greater shoot/root FW ratio. Seedlings from both treatmentshad similar shoot K+ concentrations, but the root K+ concentrationof seedlings grown In solutions containing 100 µM K+ wasless than their counterparts grown at 400 µM K+. When assayed at the same K+ concentration, unidirectional K+(86Rb+) influx into 14-d-old seedlings grown with 100 µMK+ in the nutrient solution was greater than that into seedlingsgrown with 400 µM K+ in the nutrient solution, indicatingan increased K+ influx capacity in the former. Furthermore,K+ (86Rb+) influx into seedlings grown and assayed at 100 µMK+ was greater than that into seedlings grown and assayed at400 µM K+. Since net K+ uptake was lower in the seedlingsgrown at 100 µM K+, this indicates a greater unidirectionalK+ efflux from roots in solutions containing 100 µM K+. An empirical model, based on the immobility of calcium in thephloem, was used to describe quantitatively K+ fluxes in seedlings14 d after sowing. As primary data, the composition of xylemsap and the accumulation of elements in root and shoot tissueswere determined. Xylem sap was collected either as root-pressureexudate or from excised roots immersed in nutrient solutionand subjected to a pneumatic pressure of 0.4 MPa. The K:Ca ratioin these saps differed, and led to contrasting conclusions concerningthe effect of K+ nutrition on the recirculation of K+. Basedon the K:Ca ratio in the sap obtained following the applicationof pneumatic pressure, which is thought to resemble that ofintact transpiring plants, it was calculated that the K+ fluxfrom the shoot to the root was higher in seedlings maintainedin solutions containing higher K+ concentrations. This suggeststhat a negative feedback mechanism based on K+ recirculationfrom the shoot to the root via the phloem could be a primarysignal decreasing K+ influx. Key words: K+ influx, K+ recirculation, regulation, root, rye, Secale cereale L 相似文献
3.
Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K+ below 1.5 mM K+ in the medium, whereas K+concentration in the guttated fluid still increases furtheras K+ concentration in the medium is raised. At 3 mM K+ averagevalues of guttation were 1.42.4 mm3 h1 per plantwith a K+ concentration of 1020 mM; for exuding plantsthe flow was 4.27.6 mm3 h1 per plant and K+ concentration3555 mM. Abscisic acid (ABA) at 106 to 104 M 02h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K+ exported. Threeh after addition of ABA both volume and amount of K+ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 108 to 105 M)and kinetin (5 x 106 M) progressively reduced volumeflow and K+ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin 相似文献
4.
The unidirectional Ca2+ fluxes across the plasma membrane andtonoplast were determined in both excised roots and roots ofintact seedlings of rye (Secale cereale L. cv. Rheidol). Theunidirectional Ca2+ fluxes across the plasma membrane and tonoplastmeasured in excised roots were of a similar order of magnitudeto those determined in roots of intact plants. Influx and effluxof Ca2+ across the root plasma membrane were similar (estimatedto be between 0·7 and 3·4 µmol g 相似文献
5.
Stem from three- and four-week-old Soyabean [Glycine max (L.)Merr. cv. Tracy] plants reduced from 0.3 to 0.7 µmol nitratehl gl f. wt. Leaf activity was 4.77.6 µmolnitrate hl gl f. wt. Outer stem was two to fourtimes more active at reducing nitrate than was inner stem. Plantnitrate nutrition had a strong effect upon the ratio of activitypresent in stem and leaf. More nitrate increased the proportionpresent in leaves. Glycine max L., soyabean, nitrate assimilation, nitrogen metabolism, Rhizobium japonicum 相似文献
6.
Potassium-Ammonium Uptake Interactions in Tobacco Seedlings 总被引:6,自引:0,他引:6
SCHERER HEINRICH W.; MACKOWN CHARLES T.; LEGGETT J. EVERETT 《Journal of experimental botany》1984,35(7):1060-1070
Short-term (< 12 h) uptake experiments were conducted with67-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K+ andNH4+. At equal solution concentrations (0.5 mol m3) netK+ uptake was inhibited 3035% by NH4+ and NH4+ uptakewas decreased 924%. Removal of NH4+ resulted in completerecovery in K+ uptake rate, but NH4+ uptake rate did not recoverwhen K+ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m3. The relative effectof K+-NH4+ interactions was not altered when Cl- was replacedwith SO42, but the magnitudes of the uptake rates wereless in the absence of Cl-. The Vmax for NH4+ uptake was reducedfrom 128 to 105 µmol g1 dry wt. h1 in thepresence of 0.5 mol m3 K+ and the Km for NH4+ doubledfrom 12 to 27 mmol m3 in the presence of K+. The resultsof these K+-NH4+ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K+ coupled to NH4+influx via an antiporter cannot be ruled out as contributingto the decrease in net K+ uptake. Key words: Nicotiana tabacum, K+, NH4+, Uptake interactions 相似文献
7.
The Occurrence of Nitrate Reduction in the Leaves of Woody Plants 总被引:13,自引:1,他引:12
Nitrate reductase activities greater than 02 µmol h1g1 f. wt, measured by an in vivo assay, occurred in 41per cent of a large sample (555 species) of woody plants. Ifseveral taxonomic groups (Gymnosperms, Ericaceae and Proteaceae)with consistently low activities were discounted activitiesgreater than 02 µmol h1 g1 f. wt occurredin 73 per cent of the species. This compares with 93 per centin herbaceous species, suggesting that leaf nitrate reductionis of common occurrence in woody plants. In a small sample ofspecies leaf nitrate reductase activity correlated with nitrateconcentration in the xylem sap. Low activities occurred consistentlyin the Gymnosperms, Ericaceae and Proteaceae. Feeding cut shootsof representatives of these groups with nitrate caused inductionof leaf nitrate reductase activity in the Gymnosperms and Proteaceae,but only limited induction in the Ericaceae. The Ericaceae,with the exception of two species, had low activities and lownitrate reductase inducibility. Root assimilation may predominatein the Gymnosperms and Proteaceae. It is suggested that nitratereduction generally occurs in the leaves of trees from a varietyof plant communities and that this may be related to the lowerenergy cost of leaf, as opposed to root, nitrate assimilation. Nitrate reductase, trees and shrubs, leaves, nitrate assimilation, nitrate translocation, nitrate reductase induction, energy cost, plant ecology 相似文献
8.
MEMON ABDUL RAZAQUE; SIDDIQI M. YAEESH; CLASS ANTHONY D. M. 《Journal of experimental botany》1985,36(1):79-90
Barley (Hordeum vulgare L.) varieties differed in their raponseto [K+]0, in terms of their utilization efficiencies (UE = freshweight. concentration of [K+]11). At low [K+]0, Compana,an efficient-non-responder demonstrated superior utilizationof absorbed K+. On the other hand, at high [K+]0, Fergus (anefficient responder) and BT 334 (an inefficient responder) hadhigher UE values for K+ than Compana which performed poorlyat this [K+]0. Kinetic parameters for K+ activation of the enzyme pyruvatekinase from 12 barley varieties, representing a range of UEvalues, were determined. Varieties showed substantial differencesin their Vmax values (P<0·01). Compana, an efficientvariety, had the highest Vmax (31 µmol g1 freshwt. h1) which was about 50% higher than that of Mingo,an inefficient variety. By contrast, Km values for the enzymeswere not significantly different among varieties The mean valuesfor all varieties (3·9±0·15 mol m3K+) is far below the estimated cytoplasmic [K+] (100-200 molm3). It is, therefore, unlikely that differences in theutilization of K+ by these varieties can be explained on thebasis of differential requirements for (K+) activation of theseenzymes. Alternative possibilities for differences in the utilizationof K+ are discussed. Key words: K+ utilization efficiency, Pyruvate kinase, Barley varieties 相似文献
9.
K+ supplementation increases muscle [Na+-K+-ATPase] and improves extrarenal K+ homeostasis in rats 总被引:1,自引:0,他引:1
Bundgaard Henning; Schmidt Thomas A.; Larsen Jim S.; Kjeldsen Keld 《Journal of applied physiology》1997,82(4):1136-1144
Bundgaard, Henning, Thomas A. Schmidt, Jim S. Larsen, andKeld Kjeldsen. K+supplementation increases muscle[Na+-K+-ATPase]and improves extrarenal K+homeostasis in rats. J. Appl. Physiol.82(4): 1136-1144, 1997.Effects ofK+ supplementation (~200 mmolKCl/100 g chow) on plasma K+,K+ content, andNa+-K+-adeonsinetriphosphatase(ATPase) concentration([Na+-K+-ATPase])in skeletal muscles as well as on extrarenalK+ clearance were evaluated inrats. After 2 days of K+supplementation, hyperkalemia prevailed(K+-supplemented vs.weight-matched control animals) [5.1 ± 0.2 (SE) vs. 3.2 ± 0.1 mmol/l, P < 0.05, n = 5-6], and after 4 daysa significant increase in K+content was observed in gastrocnemius muscle (104 ± 2 vs. 97 ± 1 µmol/g wet wt, P < 0.05, n = 5-6). After 7 days ofK+ supplementation, a significantincrease in[3H]ouabain bindingsite concentration (344 ± 5 vs. 239 ± 8 pmol/g wet wt,P < 0.05, n = 4) was observed in gastrocnemiusmuscle. After 2 wk, increases in plasmaK+,K+ content, and[3H]ouabain bindingsite concentration in gastrocnemius muscle amounted to 40, 8, and 68%(P < 0.05) above values observed inweight-matched control animals, respectively. The latter change wasconfirmed by K+-dependentp-nitrophenyl phosphatase activitymeasurements. Fasting for 1 day reduced plasmaK+ andK+ content in gastrocnemius musclein rats that had been K+supplemented for 2 wk by 3.1 ± 0.3 mmol/l(P < 0.05, n = 5) and 15 ± 2 µmol/g wet wt(P < 0.05, n = 5), respectively. After induction of anesthesia, arterial plasma K+was measured during intravenous KCl infusion (0.75 mmolKCl · 100 g bodywt1 · h1).The K+-supplemented fasted groupdemonstrated a 42% (P < 0.05) lower plasma K+ rise, associated with asignificantly higher increase inK+ content in gastrocnemius muscleof 7 µmol/g wet wt (P < 0.05, n = 5) compared with their controlanimals. In conclusion, K+supplementation increases plasmaK+,K+ content, and[Na+-K+-ATPase]in skeletal muscles and improves extrarenalK+ clearance capacity. 相似文献
10.
Anabaena PCC 7119 showed higher rates of phosphate uptake whencells were under P-starvation. Phosphate uptake was energy-dependentas indicated the decrease observed when assays were performedin the dark or in the presence of inhibitors of photosyntheticelectron transport, energy transfer and adenosine triphosphataseactivity. Phosphate uptake was stimulated by Na+ both in P-sufficientcells and P-starved cells. Li+ and K+ acted as partial analoguesfor Na+. The Na+-stimulation of phosphate uptake followed Michaelis-Mentenkinetics, half-saturation (K) of phosphate uptake was reachedwith a Na+ concentration of 212 µM. The absence of Na+reduced the rates of phosphate uptake at all phosphate concentrationsassayed (120 µM). The maximum uptake rates (Vmax)decreased from 658 nmol P (mg dry wt)-1 h-1 in the presenceof Na+ to 149 nmol P (mg dry wt)-1 h-1 in the absence of Na+.The absence of Na+ did not change significantly the concentrationof phosphate required to reach half-saturation (K) (3.01 µMin the presence of Na+ vs 3.21 µM in the absence of Na+).In the presence of Na+ the rate of phosphate uptake was affectedby the pH; optimal rates were observed at pH 8. In the absenceof Na+ phosphate uptake was not affected by the pH; low rateswere observed in all cases. Monensin, an ionophore which collapsesNa+-gradients, reduced the rate of phosphate uptake in Na+-supplementedcells. These results indicated the existence of a Na+-dependentphosphate uptake in Anabaena PCC 7119. (Received September 8, 1992; Accepted November 17, 1992) 相似文献
11.
Cation Exchange Properties of the Cell Walls of Enteromorpha intestinalis (L.) Link. (Ulvales, Chlorophyta 总被引:6,自引:0,他引:6
The cell wall of Enteromorpha intestinalis (a marine alga) hasbeen found to behave as a weakly cross-linked cation exchangerin NaCl solutions from 0.11020 mMolal (0.11000mMolar). Anion adsorption could be described by Freundlich isothermsover this concentration range. The large anion, inulin carboxylate,was found to be a tracer of the anion free space of plant tissuesonly in salt solutions above 10 mMolal. The cell wall of Enteromorphahas a cation exchange capacity of about 2500 µ mol g1dry wt. (Na+ form). The cell wallvolume is a complex functionof pH and the NaCl concentration. As a result, the cation exchangecapacity is only predictable on a dry weight basis. The fixednegative charges of the cell wall have a pKa of2 in situ and1.75 in vitro, and seem to be a mixture of sulphate and carboxylsugar esters. The applicability of the Donnan equation to plant cell wallsis discussed. Interpretation of the cell wall as a single thermodynamicphase is shown to be inappropriate. A large proportion of thecell wall solution is unaffected by the fixed anions. 相似文献
12.
The cultivation of narrow-leafed lupins (Lupinus angustifoliusL.) increase rates of subsoil acidification, and this is thoughtto be partly related to their pattern of nutrient uptake andH+/OH- excretion. The main hypothesis of this study was thatH+ and OH- excretion is not distributed evenly over the entirelength of the root system but is limited to zones where excesscation or anion uptake occur. Seedlings of nodulated lupinswere grown in solution culture using vertically split pots thatallowed the upper and lower zones of the root system to be suppliedwith varying concentrations of K+ and NO-3. Net H+/OH- excretionwas equated to the addition of NaOH/HCl required to maintaina constant pH in the nutrient solution during a 4-d treatmentperiod and nutrient uptake was measured by depletion from solutionin each zone of the split pots. The excess of cation over anion uptake was positively correlatedwith H+ excretion in each rooting zone. In zones where K+ wassupplied at 1200 µM, cation uptake was dominated by K+and up to twice as much H+ was excreted than in zones whereK+ was absent. In zones where NO-3 was supplied at 750 µM,the anion/cation uptake was balanced, however H+ excretion continuedto occur in the zone. When NO-3 was supplied at 5000 µM,anion uptake exceeded cation uptake but there was no OH- excretion.Organic acid anions may be excreted by lupins to maintain theirinternal electroneutrality when anion uptake exceeds cationuptake. Rhizosphere pH would not increase unless the pKa ofthe excreted organic anions was greater than the external pH.Copyright1993, 1999 Academic Press Lupinus angustifolius L., H+/OH- excretion, nutrient uptake, cation-anion balance, vertical split root 相似文献
13.
WHITE P. J.; COOPER H. D.; CLARKSON D. T.; EARNSHAW M. J.; LOUGHMAN B. C. 《Annals of botany》1991,68(1):23-31
Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat 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.
Determination of Volume of Dunaliella Cells by Lithium Dilution Measurements and Derivation of Internal Solute Concentrations 总被引:1,自引:0,他引:1
A method has been developed to measure the cell volume of theunicellular green alga Dunaliella parva 19/9 using Li+ measurementsonly. Concentrations of internal solutes can also be calculatedif they are assayed in the same samples as Li+. We found thatD. parva cells grown in 0.4 kmol m3 NaCl have an averageaqueous cell volume of 65.1 ?2.9 µm3, a K+ concentrationof 126?6 mol m3, a Na+ concentration of 11?11 mol m3and a glycerol concentration of 615?27 mol m3 (n= 12).Algae grown in 1.5 kmol m3 NaCl have an average aqueouscell volume of 131 ?7.5 µm3, a K+ concentration of 109?4mol m3, a Na+ concentration of 10?39 mol m3 anda glycerol concentration of 1 425?59 mol m3 (n = 12).These results indicate that D. parva cells adapted to high salinitieshave larger cell volumes than those adapted to lower salinities.However, there is no evidence for a significant difference ininternal Na+ concentration, despite the almost 4-fold differencein the concentration of external NaCl. The intracellular glycerolconcentration alone accounts for 65% and 54%, respectively,of the osmotic balance in low and high salt grown cells. Key words: Dunaliella, cell volume, intracellular solutes 相似文献
16.
The Interaction Between Silicon and Aluminium in Sorghum bicolor (L.) Moench: Growth Analysis and X-ray Microanalysis 总被引:2,自引:0,他引:2
Seeds of Sorghum bicolor (L.) Moench. were germinated on moistfilter paper for 6 d, before the seedlings were transferredto pots containing 500 µmol l-1 Ca(NO3)2 for 2 d. Theseedlings were then treated with 0 or 100 µmol l-1 Alin factorial combination with 0, 1400 or 2800 µmol l-1Si for 8 d. The background solution used throughout was 500µmol l-1 Ca(NO3)2. Aluminium treatment reduced root growthand caused a significant increase in shoot/root ratio. The presenceof silica in the solution significantly ameliorated the effectsof aluminium on root growth. Three treatment were selected for a microanalytical investigationof the basal region of the root: 2800 µmol l-1 Si only;100 µmol l-1 Al only; and a combination of the two. Inthe 2800 µmol l-1 treatment silica was deposited in theendodermis, with the greatest accumulation being in the innertangential wall (ITW). When plants were treated with 100 µmoll-1 Al only, aluminium concentration was highest in the outertangential wall (OTW) of the epidermis. The element was presentin the hypodermal walls and OTW of the endodermis and was notdetectable in the stele. With both 2800 µmol l-1 Si and100 µmol l-1 Al in the nutrient solution the two biomineralizationsites were the ITW of the endodermis, where silicon was themajor element deposited, and atypically in the OTW of the epidermiswhere both aluminium and silicon were present. The sequestrationof aluminium in the Al-Si deposit in the OTW of the epidermismay represent the mechanism that allows greater root growthin this treatment.Copyright 1993, 1999 Academic Press Sorghum bicolor (L.) Moench., aluminium, silicon, calcium, root, toxicity, biomineralization, X-ray microanalysis, freeze substitution 相似文献
17.
Bull R Marengo JJ Finkelstein JP Behrens MI Alvarez O 《American journal of physiology. Cell physiology》2003,285(1):C119-C128
We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca2+ concentration ([Ca2+]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 12631277, 1998), with low, moderate, and high maximal fractional open times (Po). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic [Ca2+]. At 10 µM [Ca2+], low-Po channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (KaATP) = 422 µM] than moderate-Po channels (KaATP = 82 µM). Oxidation of low-Po channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-Po channels and decreased KaATP from 422 to 82 µM. At 0.1 µM cytoplasmic [Ca2+], ATP induced an almost negligible activation of low-Po channels. After oxidation to high-Po behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-Po channels at 10 µM [Ca2+] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine 相似文献
18.
Drew, M. C. and Lauchli, A. 1986. The role of the mesocotylin sodium exclusion from the shoot of Zea mays L. (cv. Pioneer3906).J. exp. Bot. 38: 409418. The mesocotyl, located between the root and shoot, can stronglyaccumulate Na+ from the ascending transpiration stream, therebypotentially acting as a sink to protect the shoot from excessNa+. To determine the quantitative importance of the mesocotylas a Na+ sink, we grew plants with either short (9·0mm) or long(21 mm) mesocotyls, the latter resembling the sizefound in field-grown plants. At 13 d, plants were transferredfrom Na + -free nutrient solution to a 22Na+ labelled solutionin which the concentration of NaCl was (mol m3) 1·0,10 or 100. The concentration of Na+ accumulated in the mesocotylin 24 h (g1 fr. wt.) exceeded that in the roots thatwere directly exposed to the nutrient solution. The amountsof 22Na+ retained in the long mesocotyl were about double thatin the short ones and increased with time of exposure and NaClconcentration. At 1·0 and 10 mol m3 NaCl, theamounts of 22Na+ retained in the mesocotyl were 619%of those reaching the shoot in 24 h, but with 100 mol m3NaCl, a damaging concentration for maize, this declined to 38%.The mesocotyl, even as a fully elongated structure is, therefore,unlikely to provide an appreciable alternative sink for Na+when NaCl reaches injurious concentrations. Key words: Ion transport, potassium, roots, salinity 相似文献
19.
Influx and Efflux of Nitrate and Ammonium in Italian Ryegrass and White Clover Roots: Comparisons Between Effects of Darkness and Defoliation 总被引:9,自引:2,他引:7
Seedlings of Italian ryegrass (Lolium multiflorum Lam. cv. RVP)and clonal stolon cuttings of white clover (Trifolium repensL. cv. Blanca) were grown for 19 d in flowing solution culture,with N supplied as either 250 mmol m3 NO3 or NH3+.Rates of net uptake, influx and translocation of NO3and NH4+ were then determined using 15N and 13N labelling techniques:between 35 h into the photoperiod following 8 h darknessfor white clover (CL), and for ryegrass plants that were eitherentire (IL) or with shoots excised 90 min prior to 13N influx(IC); and 75 min into the photoperiod following 3739h darkness for ryegrass (ID). Rates of net uptake, influx andefflux of NH4+ exceeded those of NO3 in IL and IC ryegrassplants: the opposite occurred in white clover (CL). The decreasein net uptake following defoliation of ryegrass was greaterfor NH4+ (62%) than NO3 (40%). For NH4+ this was associatedwith a large decrease in influx from 110 to 6.0µmol h1g1 root fr. wt; but for NO3, influx only decreasedfrom 42 to 37 µmol h1 g1. Prolonged exposureto darkness (ID plants) also lowered net uptake of NO3and NH4+ by, respectively, 86% and 95% of IL levels. For NH4+this was characterized by a large decrease in influx and a smalldecrease in efflux; whilst for NO3 the effect of a largedecrease in influx was reinforced by a smaller increase in efflux. The data were used to estimate the translocatory fluxes of NO3(0320µmol h1 g1) and NH4+ (0030.4µmolh1 g1), assimilation in the roots of NO3(0226µmol h1 g1) and NH+4 (0589 µmolh1 g1), and the concentrations of NO3 (915mol m3) in the cytoplasmic compartment of the roots.The relevance of variable influx and efflux to models for theregulation of N uptake is discussed. Key words: Lolium multiflorum, Trifolium repens, influx, efflux, nitrate, ammonium, 13N 相似文献
20.
Two-node explants from Sweet Orange cv. St Ives Valencia orangeshoots produced prolific callus and formed secondary abscissionzones within internodes when cultured in vitro with abscisicacid (ABA, 5 µM) or -naphthaleneacetic acid (NAA, 5 µM).Benzyladenine (BA, 1 µm) induced callus but had littleeffect on abscission. Secondary abscission zone formation wasassociated with ABA-induced and auxin-induced ethylene formation.Treatment of explants with inhibitors of ethylene synthesis[aminoethoxyvinyl glycine (AVG), Co2+, PO43] preventedformation of secondary abscission zones but had variable effectson callus formation. Newly made explants contained high concentrationsof endogenous ABA (up to 6000 ng g1 f.wt), as measuredby GC/MS/SIM. Long-term subculture of explants (two years) inmedia containing BA (1 µm) led to a reduction in endogenousABA level (40 ng g1 f. wt) and to loss of capacity toform extensive callus and secondary abscission zones. Citrus sinensis (L.) Osbeck cv. St Ives Valencia, sweet orange, secondary abscission zones, in vitro, ethylene, endogenous ABA, endogenous IAA 相似文献