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1.
The effects of light on induction, time courses, and kinetic patterns of net nitrate uptake in barley 总被引:4,自引:1,他引:3
Barley seedlings ( Hordeum vulgare L.) were grown hydroponically with (induced) or without (uninduced) nitrate in a light/dark cycle with high photon flux density to determine the effects of light on time courses, induction and kinetics of net nitrate uptake. Nitrate uptake was induced by external nitrate in both light and dark and was prevented by 1 mol m–3 p-fluorophenylalanine. In high light, nitrate uptake was about 2-fold higher than in low light. During time course experiments the uptake rates oscillated due to daily light–dark changes. Rates of nitrate uptake also increased at about 2200 h during continuous darkness. This increase coincided approximately with the time at which the dark period started during the previous culture of the plants, indicating that it was due to a mechanism associated with an endogenous diurnal rhythm. When calculating the kinetics of nitrate uptake, a model with two saturable systems, including a high-affinity system (HATS) and a low-affinity system (LATS), gave the best fit to data in all treatments. The apparent affinity of the HATS ranged from 7·7 to 12·2 mmol m–3 in induced plants in all light conditions. The effect of light on the HATS was mainly an increase of apparent V max in the step from low to high light. In uninduced plants the HATS operated at a very low activity which was strongly enhanced during induction. Interpretation of the calculated kinetics of the LATS was much more difficult on the basis of net uptake data. The apparent affinity of the LATS increased from 24·3 mol m–3 in low light up to 0·17 mol m–3 after acceleration in high light. These extreme changes in apparent affinity of the LATS could not be explained satisfactorily, and the nature of this system is also discussed with respect to the method used. 相似文献
2.
The uptake of [36Cl]chlorate by the 14U variant of the XD cell line of Nicotiana tobaccum L. cv Xanthi was investigated to examine the use of chlorate as a nitrate analog in transport studies. The kinetics of chlorate uptake against concentration was complex. Evidence was obtained, e.g., by means of nitrate competition, that these kinetics could be resolved into two components indicating the existence of two influx mechanisms: a saturable high affinity transport system (HATS) and a low affinity transport system (LATS) that showed first order kinetics. HATS has an apparent Km for chlorate of 0.3 millimolar, and a marked pH dependence. The Vmax dropped about fivefold as the pH was changed from the optimum pH (5.5-6.5), while the Km remained virtually unchanged. The activity of HATS was completely inhibited by 15 millimolar nitrate and was less sensitive to chloride. LATS was inhibited by chloride and showed some inhibition by nitrate. It was concluded that [36Cl]chlorate can be used as an analog for nitrate uptake studies only in a limited low concentration range where HATS is the main route for chlorate influx. 相似文献
3.
Salinity remarkably inhibits NO3 - uptake but the mechanisms are not well understood. This study was addressed to elucidate the role of ionic and osmotic components of salinity on NO3 - influx and efflux employing classic kinetics involving a low affinity transport system (LATS) and a high affinity transport system (HATS). In the presence of KCl, NaCl, and Na2SO4 at 100 mM concentrations, in both LATS and HATS, Michaelis constant (Km) was similar for the three salts and maximum rate (Vmax) decreased as follows: KCl > NaCl > Na2SO4, compared to control indicating a non-competitive interaction with NO3 -. Unexpectedly, iso-osmotic solutions (osmotic potential Ψπ = -0.450) of polyethylene glycol (PEG, 17.84 %, v/v) and mannitol (100 mM) remarkably increased Km in both the LATS and the HATS, but Vmax did not change indicating a competitive inhibition. Under the PEG and mannitol treatments, Km and Vmax were higher than under the salt treatments. The salts increased slightly NO3 - efflux in the following order KCl > NaCl > Na2SO4. In contrast, mannitol strongly stimulated and the PEG inhibited NO3 - efflux. The obtained data reveal that salinity effects were not dependent on the anion type (Cl- versus SO4 2-) indicating a non-competitive inhibition mechanism between Cl- and NO3 -. In contrast, the cation types (K+ versus Na+) had a pronounced effect. The osmotic component is important to net NO3 - uptake affecting remarkably the influx in both LATS and HATS components of cowpea roots. 相似文献
4.
Transmembrane electrical potential differences (Δψ) of epidermal and cortical cells were measured in intact roots of barley (Hordeum vulgare L. cv Klondike). The effects of exogenous NO3− on Δψ (in the concentration range from 100 micromolar to 20 millimolar) were investigated to probe the mechanisms of nitrate uptake by the high-affinity (HATS) and low-affinity (LATS) transport systems for NO3− uptake. Both transport systems caused depolarization of Δψ, demonstrating that the LATS (like the HATS) for NO3− uptake is probably mediated by an electrogenic cation (H+?) cotransport system. Membrane depolarization by the HATS was “inducible” by NO3−, and saturable with respect to exogenous [NO3−]. By contrast, depolarization by the LATS was constitutive, and first-order in response to external [NO3−]. H+ fluxes, measured in 200 micromolar and in 5 millimolar Ca(NO3)2 solutions, failed to alkalinize external media as anticipated for a 2 H+:1 NO3− symport. However, switching from K2SO4 solutions (which were strongly acidifying) to KNO3 solutions at the same K+ concentration caused marked reductions in H+ efflux. These observations are consistent with NO3− uptake by the HATS and the LATS via 2 H+:1 NO3− symports. These observations establish that the HATS for nitrate uptake by barley roots is essentially similar to those reported for Lemna and Zea mays by earlier workers. There are, nevertheless, distinct differences between barley and corn in their quantitative responses to external NO3−. 相似文献
5.
Miguel Cerezo Gemma Cama?es Víctor Flors Eduardo Primo-Millo Pilar García-Agustín 《Plant signaling & behavior》2007,2(5):337-342
Previously, we reported that in Citrus plants, nitrate influx through the plasmalemma of roots cells follows a biphasic pattern, suggesting the existence of at least two different uptake systems, a high and low affinity transport system (HATS and LATS, respectively). Here, we describe a novel inducible high affinity transport system (iHATS). This new nitrate transport system has a high capacity to uptake nitrate in two different Citrus rootstocks (Cleopatra mandarin and Troyer citrange). The iHATS was saturable, showing higher affinity than constitutive high affinity transport system (cHATS) to the substrate NO3−. The Vmax for this saturable component iHATS was higher than cHATS, reaching similar values in both rootstocks.Additionally, we studied the regulation of root NO3− uptake mediated by both HATS (iHATS and cHATS) and LATS. In both rootstocks, cHATS is constitutive and independent of N-status. Concerning the regulation of iHATS, this system is upregulated by NO3− and down-regulated by the N status and by NO3− itself when plants are exposed to it for a longer period of time. LATS in Cleopatra mandarin and Troyer citrange rootstocks is repressed by the N-status.The use of various metabolic uncouplers or inhibitors indicated that NO3− net uptake mediated by iHATS and LATS was an active transport system in both rootstocks.Key Words: Citrus, inducible high affinity transport system (iHATS), constitutive high affinity transport system (cHATS), nitrate uptake, regulation 相似文献
6.
Salt activation and inhibition of membrane ATPase from roots of the halophyte Atriplex nummularia 总被引:1,自引:0,他引:1
H. R. LERNER LEONORA REINHOLD RACHEL GUY YAEL BRAUN MIRIAM HASIDIM ALEXANDRA POLJAKOFF-MAYBER 《Plant, cell & environment》1983,6(6):501-506
Abstract Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep-tible to inhibition by KC1 or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m?3. At pH 8 stimulation occurred at 50 mol m?3 but concentrations above 100 mol m?3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m?3 of NaCl or KC1; concentrations higher than 150 mol m?3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m?3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m?3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity. 相似文献
7.
Effects of silicon on enzyme activity and sodium,potassium and calcium concentration in barley under salt stress 总被引:35,自引:1,他引:35
Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown
in a hydroponics system containing 120 mol m-3 NaCl only and 120 mol m-3 NaCl with 1.0 mol m-3 Si (as potassium silicate). Compared with the plants treated with salt alone, superoxide dismutase (SOD) activity in plant
leaves and H+-ATPase activity in plant roots increased, and malondialdehyde (MDA) concentration in plant leaves decreased significantly
for both cultivars when treated with salt and Si. The addition of Si was also found to reduce sodium but increase potassium
concentrations in shoots and roots of salt-stressed barley. Sodium uptake and transport into shoots from roots was greatly
inhibited by added Si under salt stress conditions. However, Si addition exhibited little effect on calcium concentrations
in shoots of salt-stressed barley. Thus, Si-enhanced salt tolerance is attributed to selective uptake and transport of potassium
and sodium by plants. The results of the present study suggest that Si is involved in the metabolic or physiological changes
in plants.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Pea seedlings (Pisum sativum L. cv ‘Kleine Rheinlän-derin’) were grown hydroponically in solutions containing either nitrate (3 or 14 mol m−3) or ammonium (3 mol m−3) as the nitrogen source. Ammonium nutrition as such had no negative effect on plant biomass production, but drastically increased the sensitivity to moderate salinity (50 mol m−3 NaCl). The reasons for this effect are investigated here and in a subsequent paper. The appearance of visible symptoms of salt damage (wilting of marginal leaf areas followed by progressive necrosis) was paralleled by the development of several characteristic modifications in the solute and metabolite contents. Major changes were: (i) high salt (NaCl) accumulation in leaves; (ii) accumulation of ammonium (up to 20 mol m−3) and amino acids (up to 110 mol m−3) in leaves, but at decreased ammonium uptake rates; and (iii) decreased protein content. In a comparison paper we report on the subcellular distribution of salts, ammonium and metabolites under the above conditions. 相似文献
9.
《Plant and Soil》2000,220(1-2):175-187
Several studies have previously shown that shoot removal of forage species, either by cutting or herbivore grazing, results
in a large decline in N uptake (60%) and/or N2 fixation (80%). The source of N used for initial shoot growth following defoliation relies mainly on mobilisation of N reserves
from tissues remaining after defoliation. To date, most studies investigating N-mobilisation have been conducted, with isolated
plants grown in controlled conditions. The objectives of this study were for Lolium perenne L., grown in a dense canopy in field conditions, to determine: 1) the contribution of N-mobilisation, NH4
+ uptake and NO3
- uptake to growing shoots after defoliation, and 2) the contribution of the high (HATS) and low (LATS) affinity transport
systems to the total plant uptake of NH4
+ and NO3
-. During the first seven days following defoliation, decreases in biomass and N-content of roots (34% and 47%, respectively)
and to a lesser extent stubble (18% and 43%, respectively) were observed, concomitant with mobilisation of N to shoots. The
proportion and origin of N used by shoots (derived from reserves or uptake) was similar to data reported for isolated plants.
Both HATS and LATS contributed to the total root uptake of NH4
+ and NO3
-. The Vmax of both the NH4
+ and NO3
- HATS increased as a function of time after defoliation, and both HATS systems were saturated by substrate concentrations
in the soil at all times. The capacity of the LATS was reduced as soil NO3
- and NH4
+ concentrations decreased following defoliation. Data from 15N uptake by field-grown plants, and uptake rates of NH4
+ and NO3
- estimated by excised root bioassays, were significantly correlated, though uptake was over-estimated by the later method.
The results are discussed in terms of putative mechanisms for regulating N uptake following severe defoliation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
Thornton B 《Journal of experimental botany》2004,55(397):761-769
Plants of Lolium perenne L. were grown in sterile solution culture supplied with 2 mol m(-3) nitrogen as either nitrate or ammonium. Glutamine at 5 mol m(-3) was added to the nutrient solution of half the plants for 24 h. Root nitrate influx (at external nitrate concentrations 0-2000 mmol m(-3)) and amino acid concentrations were determined. In a second experiment the concentration of the added glutamine was varied from 0-5 mol m(-3) and nitrate influx determined at 250 and 2000 mmol m(-3). The maximum rate of influx attributed to the high affinity transport system (HATS) was reduced by 66% by the presence of glutamine achieved through an 84% reduction in its constitutive component and a 59% reduction in its inducible component. Influx attributed to LATS was unaffected by the addition of glutamine. The inhibition of total nitrate influx by glutamine was positively related to the contribution of HATS to the total influx. In both nitrate- and ammonium-grown plants, the concentration of glutamine required to inhibit nitrate influx significantly was lower when influx was determined at 250 mmol m(-3) compared with 2000 mmol m(-3) nitrate. The addition of glutamine increased its concentrations in root tissue. However, the results cannot be attributed to changes in glutamine alone as its addition also resulted in increased concentrations of other amino acids. Implications for plants growing under field conditions are discussed. 相似文献
11.
In view of the need to exploit saline water resources in agriculture in arid zones, we investigated the salt tolerance of Opuntia ficus-indica in plants growing in solution culture. Salt (NaCl) was added in concentrations ranging from 5 (control) to 200 mol m-3. Cladode growth was sensitive to salinity, being 60% of the control at 50 mol m-3 NaCl. The root-to-stem ratio decreased significantly only at 200 mol m-3. Various other parameters were studied, such as water content, Na, K and Cl content, osmotic pressure, and CO2 uptake. Of these parameters the decreases in cladode water content and CO2 uptake were related to the decrease in cladode growth. Raised salinity increased cladode osmotic pressure, which was associated with tissue dehydration. We concluded that osmotic adjustment does not occur in prickly pear under salt stress. 相似文献
12.
Abstract Salt-stressed plants often show Ca deficiency symptoms. The effects of NaCl salinity (1 to 150 mol m-3) and supplemental Ca (10 mol m-3) on Na and Ca transport in barley (Hordeum vulgare L.) and their relationship to growth were investigated. The adjustment of Na and Ca transport was investigated by examining young seedlings exposed to short-term (immediate) and long-term (7 d) exposure to salinity. When the plants were exposed to long-term treatments of salinity, the rate of sodium accumulation in roots was approximately 10 to 15% of short-term treatments. No significant adjustment in the transport to the shoot was observed. Rates of tracer (22Na) transport were compared to calculated rates based on relative growth rates and tissue element concentrations. Comparisons between measured tracer and calculated rates of transport indicate that 22Na transport may underestimate transport to the shoot because of dilution of the tracer in the root cytoplasm. Calcium uptake showed only minor adjustment with time. Measured rates of tracer transport to the shoot correlated well with calculated values. The transport and tissue concentrations of Na were significantly affected by supplemental Ca. Calcium transport and tissue concentrations were markedly inhibited by salinity. Supplemental Ca increased Ca transport and accumulation at all NaCl treatments above that of control plants without supplemental Ca. Salinity inhibited plant growth at 150 mol m -3NaCl, but not at 75 mol m-3. Supplemental Ca significantly improved root length but not fresh weight after 7d of salinity, although differences in fresh weight were detected after 9d. There were significant Na-Ca interactions with ion transport, ion accumulation, and growth. The effects of salinity on Na and Ca transport to the shoot do not appear to play a major role in shoot growth of barley. 相似文献
13.
A comparative kinetic analysis of nitrate and ammonium influx in two early-successional tree species of temperate and boreal forest ecosystems 总被引:6,自引:1,他引:6
Xiangjia Min M. Yaeesh Siddiqi Robert D. Guy Anthony D. M. Glass & Herbert J. Kronzucker 《Plant, cell & environment》2000,23(3):321-328
Root NO3 ? and NH4 + influx systems of two early‐successional species of temperate (trembling aspen: Populus tremuloides Michx.) and boreal (lodgepole pine: Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) forest ecosystems were characterized. NO3 ? and NH4 + influxes were biphasic, consisting of saturable high‐affinity (HATS) and constitutive non‐saturable low‐affinity transport systems (LATS) that were evident at low and relatively high N concentrations, respectively. NO3 ? influx via HATS was inducible (IHATS); nitrate pre‐treatment resulted in 8–10‐fold increases in the Vmax for influx in both species. By contrast, HATS for NH4 + were entirely constitutive. In both species, Vmax values for NH4 + influx were higher than those for NO3 ? uptake; the differences were larger in pine (6‐fold) than aspen (1·8‐fold). In aspen, the Km for NH4 + influx by HATS was approximately 3‐fold higher than for IHATS NO3 ? influx, while in pine the Km for IHATS NO3 ? influx was approximately 3‐fold higher than for NH4 + influx. The aspen IHATS for NO3 ? influx appeared to be more efficient than that of pine (Vmax values for aspen being approximately 10‐fold higher and Km values being approximately 13‐fold lower than for pine). By contrast, only small differences in values for the NH4 + HATS were evident between the two species. The kinetic parameters observed here probably result from adaptations to the N availabilities in their respective natural habitats; these may contribute to the distribution and niche separation of these species. 相似文献
14.
Greenhouse-grown cut flower roses are often irrigated with moderately saline irrigation water. The salt/ballast ions are either present initially in poor quality raw water or reclaimed municipal water, or accumulated in greenhouse irrigation water that is captured and reused. Such ions can inhibit root absorption of essential nutrients. The objective of this work was to quantify the influence of NaCl concentration on the uptake of nitrate and potassium by roses and develop a predictive model of uptake inhibition based on NaCl, NO3 ?, and K+ concentration. One year-old rose plants (Rosa spp. ‘Kardinal’ on ‘Natal Briar’ rootstock) were moved into growth chambers where nitrogen and potassium depletion were monitored during 6 days. Eight different initial NaCl treatments varying from zero to 65 mol m?3 were used and within these there were two initial NO3 ? and K+ concentrations: high concentration (HC, 7.0 mol m?3 and 2.6 mol m?3 NO3 ? and K+ respectively) or low concentration (LC, 3.5 mol m?3 and 1.3 mol m?3 NO3 ? and K+ respectively). Plant NO3 ? uptake was negatively affected by NaCl concentration. NO3 ? maximum influx (Imax) declined from 5.1 µmol to 2.5 µmol per gram of plant dry weight per hour as NaCl concentration increased from zero to 65 mol m?3. A modified Michaelis–Menten (M–M) equation taking into account inhibition by NaCl provided the best fit for NO3 ? uptake in response to varying NaCl concentration. K+ uptake was unaffected by NaCl concentration. A M–M equation that did not include inhibition was suitable for describing K+ uptake at varying NaCl concentration. The resulting empirical models could assist with decision making, such as: adjustment of NO3 ? fertilization based on NaCl concentration, necessity of water desalinization, or determination of the desired leaching fraction. 相似文献
15.
Nitrate and ammonium absorption by plants growing at a sufficient or insufficient level of phosphorus in nutrient solutions 总被引:1,自引:0,他引:1
J. K. Schjørring 《Plant and Soil》1986,91(3):313-318
Summary Absorption of nitrate and ammonium was studied in water culture experiments with 4 to 6 weeks old plants of barley (Hordeum vulgare L.), buckwheat (Fagopyrum esculentum L. Moench) and rape (Brassica napus L.). The plants were grown in a complete nutrient solution with nitrate (5.7±0.2 mM) or nitrate (5.6±0.2 mM) + ammonium (0.04±0.02 mM). The pH of the nutrient solution was kept at 5.0 using a pH-stat. It was found that phosphorus deficiency reduced the rate of nitrate uptake by 58±3% when nitrate was the sole N source and by 83±1% when both nitrate and ammonium were present. The reduction occurred even before growth was significantly impeded by P deficiency. The inhibition of the uptake of ammonium was less,i.e. ammonium constituted 10±1% of the total N uptake in the P sufficient plants and 30±5% in the P deficient plants. The reduction of nitrate absorption greatly decreased the difference between the uptake of anions and cations. It is suggested that P deficiency reduced the assimilation of NO
3
–
into the proteins, which might cause a negative feedback on NO
3
–
influx and/or stimulate NO
3
–
efflux. 相似文献
16.
Rapid, Reversible Inhibition of Nitrate Influx in Barley by Ammonium 总被引:18,自引:2,他引:16
The rate of influx of nitrate into the roots of intact barleyplants was measured over a period of 35 min from externalnitrate concentrations of 1150 mmol m3, using13N-labelled nitrate as tracer. Ammonium at external concentrationsof 0.00550 mol m3 inhibited nitrate influx ina manner which did not conform to a simple kinetic model butincreased approximately as the logarithm of the ammonium concentration.At any particular ammonium concentration, inhibition of nitrateinflux reached its full extent within 3 min of the ammoniumbeing supplied and was not made more severe by up to 17 minpre-treatment with ammonium. On removing the external ammonium,nitrate influx returned to its original rate within about 3min. Potassium at 0.00550 mol m3 did not reproducethe rapid effect of ammonium on nitrate influx. Net uptake of nitrate also decreased when ammonium was supplied,over a similar timescale and to a similar extent as nitrateinflux. The decrease in nitrate influx caused by ammonium wassufficient to account for the observed reduction in net uptake,without necessitating any acceleration of nitrate efflux. Key words: Hordeum vulgare, roots, ion transport, short-lived isotopes, 13N 相似文献
17.
Compartmental nitrate concentrations in barley root cells measured with nitrate-selective microelectrodes and by single-cell sap sampling 总被引:18,自引:0,他引:18
Rui-Guang Zhen Hans-Werner Koyro Roger A. Leigh A. Deri Tomos Anthony J. Miller 《Planta》1991,184(3):356-361
Nitrate-selective microelectrodes were used to measure intracellular nitrate concentrations (as activities) in epidermal and cortical cells of roots of 5-d-old barley (Hordeum vulgare L.) seedlings grown in nutrient solution containing 10 mol · m–3 nitrate. Measurements in each cell type grouped into two populations with mean (±SE) values of 5.4 ± 0.5 mol · m–3 (n=19) and 41.8 ± 2.6 mol · m–3 (n = 35) in epidermal cells, and 3.2 ± 1.2 mol · m–3 (n = 4) and 72.8 ± 8.4 mol · m–3 (n = 13) in cortical cells. These could represent the cytoplasmic and vacuolar nitrate concentrations, respectively, in each cell type. To test this hypothesis, a single-cell sampling procedure was used to withdraw a vacuolar sap sample from individual epidermal and cortical cells. Measurement of the nitrate concentration in these samples by a fluorometric nitrate-reductase assay confirmed a mean vacuolar nitrate concentration of 52.6 ± 5.3 mol · m–3 (n = 10) in epidermal cells and 101.2 ± 4.8 mol · m–3 (n = 44) in cortical cells. The nitrate-reductase assay gave only a single population of measurements in each cell type, supporting the hypothesis that the higher of the two populations of electrode measurements in each cell type are vacuolar in origin. Differences in the absolute values obtained by these methods are probably related to the fact that the nitrate electrodes were calibrated against nitrate activity but the enzymic assay against concentration. Furthermore, a 28-h time course for the accumulation of nitrate measured with electrodes in epidermal cells showed the apparent cytoplasmic measurements remained constant at 5.0 ± 0.7 mol · m–3, while the vacuole accumulated nitrate to 30–50 mol · m–3. The implications of the data for mechanisms of nitrate transport at the plasma membrane and tonoplast are discussed.Symbol
n
2
Chi-squared with n degrees of freedom
R.-G.Z. was awarded a Sino-British Friendship Scholarship sponsored by the British Council and H.-W.K. was supported by an AFRC Linked Research Grant to A.D.T for collaboration with R.A.L. We wish to thank Dr. K. Goulding for advice on ion chromatography, Dr. K. Moore for assistance with statistical analysis and Dr. J.H. Williams for advice on the microsample analysis. 相似文献
18.
The amino acid (35S-methionine) incorporating activity of an in vitro wheat germ translation system was found to be maximal in 80 to 125 mol m–3 K with 2 to 4 mol m–3 Mg both as the acetate. Substitution of Na for K, or chloride for acetate at concentrations above 80 mol m–3 inhibited incorporation. When the K acetate concentration was raised to 200 mol m–3, no incorporation of radioactive methionine occurred.Translation by polysomes extracted from leaf tissue of S. maritima, supplemented with postribosomal supernatant from wheat germ, showed activity which was optimal in the presence of 225 mol m–3 K acetate and 8 mol m–3 Mg acetate. However, the translation system was not directly comparable with the wheat germ system, as studies with an initiation inhibitor, aurintricarboxylic acid, suggested that the S. maritima system was essentially elongation-dependent, while initiation occurred in the wheat germ system.Elongation-dependent polysomal preparations were extracted from leaves of the glycophytes Pisum sativum, Triticum aestivum, Oryza sativa and Hordeum vulgare, and from the halophytes Atriplex isatidea and Inula crithmoides. Translation by polysomes from the salt-tolerant plants was optimal at higher K and Mg concentrations, than by polysomes from the glycophytes. Furthermore, NaCl was better able partially to substitute for the role of K in polysomal preparations from halophytes than glycophytes. 相似文献
19.
Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψπ) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized
to (Ψπ) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl2 or Na2SO4. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO3. The nutrient solutions were sampled for NO3 analysis each day immediately before renewing the solutions. The accumulative loss of NO3 from the solutions was considered to be uptake whereas NO3 reduction was the difference between uptake and seedling content. Lowering the (Ψπ) of the nutrient solutions resulted in decreased concentrations of NO3 in the plant, little or no effect (except at the lowest (Ψπ) level) on uptake, and increased nitrate reductase activity. Increased rates of NO3 reduction were in particular associated with the Cl concentration of the nutrient solution. 相似文献
20.
Regulation of the High-Affinity Nitrate Transport System in Wheat Roots by Exogenous Abscisic Acid and Glutamine 总被引:1,自引:0,他引:1
Chao Cai Xue-Qiang Zhao Yong-Guan Zhu Bin Li Yi-Ping Tong Zhen-Sheng Li 《植物学报(英文版)》2007,49(12):1719-1725
Nitrate is a major nitrogen (N) source for most crops. Nitrate uptake by root cells is a key step of nitrogen metabolism and has been widely studied at the physiological and molecular levels. Understanding how nitrate uptake is regulated will help us engineer crops with improved nitrate uptake efficiency. The present study investigated the regulation of the high-affinity nitrate transport system (HATS) by exogenous abscisic acid (ABA) and glutamine (Gin) in wheat (Triticum aestivum L.) roots. Wheat seedlings grown in nutrient solution containing 2 mmol/L nitrate as the only nitrogen source for 2weeks were deprived of N for 4d and were then transferred to nutrient solution containing 50 μmol/L ABA, and 1 mmol/L Gin in the presence or absence of 2 mmol/L nitrate for 0, 0.5, 1, 2, 4, and 8 h. Treated wheat plants were then divided into two groups. One group of plants was used to investigate the mRNA levels of the HATS components NRT2 and NAR2 genes in roots through semi-quantitative RT-PCR approach, and the other set of plants were used to measure high-affinity nitrate influx rates in a nutrient solution containing 0.2 mmol/L ^15N-labeled nitrate. The results showed that exogenous ABA induced the expression of the TaNRT2.1, TaNRT2.2, TaNRT2.3, TaNAR2.1, and TaNAR2.2 genes in roots when nitrate was not present in the nutrient solution, but did not further enhance the induction of these genes by nitrate. Glutamine, which has been shown to inhibit the expression of NRT2 genes when nitrate is present in the growth media, did not inhibit this induction. When Gin was supplied to a nitrate-free nutrient solution, the expression of these five genes in roots was induced. These results imply that the inhibition by Gin of NRT2 expression occurs only when nitrate is present in the growth media. Although exogenous ABA and Gin induced HATS genes in the roots of wheat, they did not induce nitrate influx. 相似文献