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1.
Net uptakes of K + and NO 3− were monitored simultaneously and continuously for two barley ( Hordeum vulgare) cultivars, Prato and Olli. The cultivars had similar rates of net K + and NO 3− uptake in the absence of NH 4+ or Cl −. Long-term exposure (over 6 hours) to media which contained equimolar mixtures of NH 4+, K +, Cl −, or NO 3− affected the cultivars very differently: (a) the presence of NH 4+ as NH 4Cl stimulated net NO 3− uptake in Prato barley but inhibited net NO 3− uptake in Olli barley; (b) Cl − inhibited net NO 3− uptake in Prato but had little effect in Olli; and (c) NH 4+ as (NH 4) 2SO 4 inhibited net K + uptake in Prato but had little effect in Olli. Moreover, the immediate response to the addition of an ion often varied significantly from the long-term response; for example, the addition of Cl − initially inhibited net K + uptake in Olli barley but, after a 4 hour exposure, it was stimulatory. For both cultivars, net NH 4+ and Cl − uptake did not change significantly with time after these ions were added to the nutrient medium. These data indicate that, even within one species, there is a high degree of genotypic variation in the control of nutrient absorption. 相似文献
2.
The influence of NH 4+, in the external medium, on fluxes of NO 3− and K + were investigated using barley ( Hordeum vulgare cv Betzes) plants. NH 4+ was without effect on NO 3− ( 36ClO 3−) influx whereas inhibition of net uptake appeared to be a function of previous NO 3− provision. Plants grown at 10 micromolar NO 3− were sensitive to external NH 4+ when uptake was measured in 100 micromolar NO 3−. By contrast, NO 3− uptake (from 100 micromolar NO 3−) by plants previously grown at this concentration was not reduced by NH 4+ treatment. Plants pretreated for 2 days with 5 millimolar NO 3− showed net efflux of NO 3− when roots were transferred to 100 micromolar NO 3−. This efflux was stimulated in the presence of NH 4+. NH 4+ also stimulated NO 3− efflux from plants pretreated with relatively low nitrate concentrations. It is proposed that short term effects on net uptake of NO 3− occur via effects upon efflux. By contrast to the situation for NO 3−, net K + uptake and influx of 36Rb +-labeled K + was inhibited by NH 4+ regardless of the nutrient history of the plants. Inhibition of net K + uptake reached its maximum value within 2 minutes of NH 4+ addition. It is concluded that the latter ion exerts a direct effect upon K + influx. 相似文献
3.
The influence of NO 3− uptake and reduction on ionic balance in barley seedlings ( Hordeum vulgare, cv. Compana) was studied. KNO 3 and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl − uptake was more rapid than the rate of NO 3− uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO 3− uptake after 4 hours resulting in a sustained rate of NO 3− uptake which exceeded the rate of Cl − uptake. The initial (2 to 4 hours) rate of K + uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K + uptake was greater with the KNO 3 treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO 3 increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K + uptake from KNO 3 did not exceed K + uptake from KCl. We suggest that the greater uptake and accumulation of K + in NO 3−-treated plants resulted from ( a) a more rapid, sustained uptake and transport of NO 3− providing a mobile counteranion for K + transport, and ( b) the synthesis of organic acids in response to NO 3− reduction increasing the capacity for K + accumulation by providing a source of nondiffusible organic anions. 相似文献
4.
A detailed examination was conducted on the linear, or first-order kinetic component for K +( 86Rb +) influx into root segments of both low- and high-salt grown corn seedlings ( Zea mays [A632 × Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl − in the uptake solution by either SO 42−, H 2PO 4−, or NO 3− caused a significant (50-60%) and specific inhibition of the linear component of K + influx. The anion transport inhibitor, 4,4′-diisothiocyano-2,2′-disulfonic acid, was found to abolish saturable Cl − influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K + uptake system; this inhibition was identical to that observed when Cl − was replaced by other anions in the K + uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K + channels in nerve axons, also caused a dramatic (70%) and specific inhibition of the linear component of K + influx, but this was obtained only in high-salt roots. The reasons for this difference are discussed with respect to the differing abilities of low- and high-salt roots to absorb tetraethylammonium. Our present results indicate that the linear component of K+ influx may occur by a passive process involving transmembrane K+ channels. Fluxes through these K+ channels may be partly coupled to a saturating Cl− influx mechanism. 相似文献
5.
Ca 2+ uptake was studied in short-term experiments using 5-day-old excised maize roots. This tissue readily absorbs Ca 2+, and inhibition by dinitrophenol and low temperature shows that the process is metabolically mediated. The uptake of Ca 2+, like that of other cations, is influenced by the counter ion, the pH and concentration of the ambient solution, and the presence of other cations. The rate of uptake from various salts decreases in the following order: NO 3− > Cl − = Br − > SO 42−. K + and H + greatly interfere with Ca 2+ absorption, while Li + and Na + have only slight effects. 相似文献
6.
Dark-grown, detopped corn seedlings (cv. Pioneer 3369A) were exposed to treatment solutions containing Ca(NO 3) 2, NaNO 3, or KNO 3; KNO 3 plus 50 or 100 millimolar sorbitol; and KNO 3 at root temperatures of 30, 22, or 16 C. In all experiments, the accelerated phase of NO 3− transport had previously been induced by prior exposure to NO 3− for 10 hours. The experimental system allowed direct measurements of net NO 3− uptake and translocation, and calculation of NO 3− reduction in the root. The presence of K + resulted in small increases in NO 3− uptake, but appreciably stimulated NO 3− translocation out of the root. Enhanced translocation was associated with a marked decrease in the proportion of absorbed NO 3− that was reduced in the root. When translocation was slowed by osmoticum or by low root temperatures, a greater proportion of absorbed NO 3− was reduced in the presence of K +. Results support the proposition that NO 3− reduction in the root is reciprocally related to the rate of NO 3− transport through the root symplasm. 相似文献
7.
The effect of the exogenous and endogenous NO 3− concentration on net uptake, influx, and efflux of NO 3− and on nitrate reductase activity (NRA) in roots was studied in Phaseolus vulgaris L. cv. Witte Krombek. After exposure to NO 3−, an apparent induction period of about 6 hours occurred regardless of the exogenous NO 3− level. A double reciprocal plot of the net uptake rate of induced plants versus exogenous NO 3− concentration yielded four distinct phases, each with simple Michaelis-Menten kinetics, and separated by sharp breaks at about 45, 80, and 480 micromoles per cubic decimeter. Influx was estimated as the accumulation of 15N after 1 hour exposure to 15NO3−. The isotherms for influx and net uptake were similar and corresponded to those for alkali cations and Cl−. Efflux of NO3− was a constant proportion of net uptake during initial NO3− supply and increased with exogenous NO3− concentration. No efflux occurred to a NO3−-free medium. The net uptake rate was negatively correlated with the NO3− content of roots. Nitrate efflux, but not influx, was influenced by endogenous NO3−. Variations between experiments, e.g. in NO3− status, affected the values of Km and Vmax in the various concentration phases. The concentrations at which phase transitions occurred, however, were constant both for influx and net uptake. The findings corroborate the contention that separate sites are responsible for uptake and transitions between phases. Beyond 100 micromoles per cubic decimeter, root NRA was not affected by exogenous NO3− indicating that NO3− uptake was not coupled to root NRA, at least not at high concentrations. 相似文献
8.
The effect of NaCl and Na 2SO 4 salinity on NO 3− assimilation in young barley ( Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO 3− transporter was affected very little; the major effect of the salts was on its activity. Both Cl − and SO 42− salts severely inhibited uptake of NO 3−. When compared on the basis of osmolality of the uptake solutions, Cl − salts were more inhibitory (15-30%) than SO 42− salts. At equal concentrations, SO 42− salts inhibited NO 3− uptake 30 to 40% more than did Cl − salts. The absolute concentrations of each ion seemed more important as inhibitors of NO 3− uptake than did the osmolality of the uptake solutions. Both K + and Na + salts inhibited NO 3− uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity. Unlike NO3− uptake, NO3− reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO3− in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the `anaerobic' in vivo assay, was always greater than the actual in situ rate of NO3− reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO3− transporter, rather than that of the NO3− reduction system, may be a critical factor to plant survival during salt stress. 相似文献
9.
Potential-dependent anion movement into tonoplast vesicles from oat roots ( Avena sativa L. var Lang) was monitored as dissipation of membrane potentials (Δψ) using the fluorescence probe Oxonol V. The potentials (positive inside) were generated with the H +-pumping pyrophosphatase, which is K + stimulated and anion insensitive. The relative rate of ΔΨ dissipation by anions was used to estimate the relative permeabilities of the anions. In decreasing order they were: SCN − (100) > NO 3− (72) = Cl − (70) > Br − (62) > SO 42− (5) = H 2PO 4− (5) > malate (3) = acetate (3) > iminodiacetate (2). Kinetic studies showed that the rate of Δψ dissipation by Cl − and NO 3−, but not by SCN −, was saturable. The Km values for Cl − and NO 3− uptake were about 2.3 and 5 millimolar, respectively, suggesting these anions move into the vacuole through proteinaceous porters. In contrast to a H +-coupled Cl − transporter on the same vesicles, the potential-dependent Cl − transport was insensitive to 4,4′-diisothiocyano-2,2′-stilbene disulfonate. These results suggest the existence of at least two different mechanisms for Cl − transport in these vesicles. The potentials generated by the H +-translocating ATPase and H +-pyrophosphatase were nonadditive, giving support to the model that both pumps are on tonoplast vesicles. No evidence for a putative Cl − conductance on the anion-sensitive H +-ATPase was found. 相似文献
10.
The investigations were focussed on the question as to whether roots of intact maize plants ( Zea mays L. cv Blizzard) release protons into deionized H 2O. Plants in the six to seven leaf stage depressed the pH of deionized H 2O from 6 to about 4.8 during an experimental period of 4 hours. Only one-third of the protons released could be ascribed to the solvation of CO 2 in H 2O. The main counter anions released were Cl −, NO 3−, and SO 42−. At low temperature (2°C), the H + release was virtually blocked while a relatively high amount of K + was released. The presence of K +, Na +, Ca 2+, and Mg 2+ in the external solution increased the H + secretion significantly. Addition of vanadate to the outer medium inhibited the H + release while fusicoccin had a stimulating effect. Substituting the nutrient solution of deionized H 2O resulted in a substantial increase of the membrane potential difference from −120 to −190 millivolts. The experimental results support the conclusion that the H + release by roots of intact maize plants is an active process driven by a plasmalemmalocated ATPase. Since the net H + release was not associated with a net uptake of K +, it is unlikely to originate from a K +/H + antiport. 相似文献
11.
Chloride or nitrate decreased a pH gradient (measured as [ 14C]methylamine accumulation) in tonoplast-enriched vesicles. The ΔpH decrease was dependent on the anion concentration. These effects are independent of the anion-sensitive H +-ATPase of the tonoplast, since the pH gradient (acid inside) was imposed artificially using a pH jump or a K + gradient and nigericin. 4,4′-Diisothiocyano-2,2′-stilbene disulfonic acid partially prevented the decrease in pH gradient induced by Cl −. Two possible models to account for this anion-dependent decrease of ΔpH are: (a) H + loss is accompanied by Cl − or NO 3− efflux from the vesicles via H +/anion symport systems on the tonoplast and (b) H + loss is accompanied by Cl − or NO 3− uptake into the vesicles via H +/anion antiport systems. Depending on the requirements and conditions of the cell, these two systems would serve to either mobilize Cl − and NO 3− stored in the vacuole for use in the cytoplasm or to drive anions into the vacuole. Chloride or nitrate also decreased a pH gradient in fractions containing plasma membrane and Golgi, implying that these membranes may have similar H +-coupled anion transport systems. 相似文献
12.
The H +-ATPase of tonoplast vesicles isolated from red beet ( Beta vulgaris L.) storage tissue was studied with respect to the kinetic effects of Cl − and NO 3−. N-Ethylmaleimide (NEM) was employed as a probe to investigate substrate binding and gross conformational changes of the enzyme. Chloride decreased the Km of the enzyme for ATP but caused relatively little alteration of the Vmax. Nitrate increased Km only. Michaelis-Menten kinetics applied throughout with respect to ATP concentration. Nitrate yielded similar kinetics of inhibition in both the presence and absence of Cl −. Other monovalent anions that specifically increased the Km of the ATPase for ATP were, in order of increasing Ki, SCN −, ClO 4−, and ClO 3−. Sulfate, although inhibitory, manifested noncompetitive kinetics with respect to ATP concentration. ADP, like NO 3−, was a competitive inhibitor of the ATPase but ADP and NO 3− did not interact cooperatively nor did either interfere with the inhibitory action of the other. It is concluded that NO 3− does not show competitive kinetics because of its stereochemical similarity to the terminal phosphoryl group of ATP. NEM was an irreversible inhibitor of the tonoplast ATPase. Both Mg·ADP and Mg·ATP protected the enzyme from inactivation by NEM but Mg·ADP was the more potent of the two. Chloride and NO 3− exerted little or no effect on the protective actions of Mg·ADP and Mg·ATP suggesting that neither Cl − nor NO 3− are involved in substrate binding. 相似文献
13.
To understand the mechanism and molecular properties of the tonoplast-type H +-translocating ATPase, we have studied the effect of Cl −, NO 3−, and 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid (DIDS) on the activity of the electrogenic H +-ATPase associated with low-density microsomal vesicles from oat roots ( Avena sativa cv Lang). The H +-pumping ATPase generates a membrane potential (Δψ) and a pH gradient (ΔpH) that make up two interconvertible components of the proton electrochemical gradient (μ h+). A permeant anion ( e.g. Cl −), unlike an impermeant anion ( e.g. iminodiacetate), dissipated the membrane potential ([ 14C]thiocyanate distribution) and stimulated formation of a pH gradient ([ 14C]methylamine distribution). However, Cl −-stimulated ATPase activity was about 75% caused by a direct stimulation of the ATPase by Cl − independent of the proton electrochemical gradient. Unlike the plasma membrane H +-ATPase, the Cl −-stimulated ATPase was inhibited by NO 3− (a permeant anion) and by DIDS. In the absence of Cl −, NO 3− decreased membrane potential formation and did not stimulate pH gradient formation. The inhibition by NO 3− of Cl −-stimulated pH gradient formation and Cl −-stimulated ATPase activity was noncompetitive. In the absence of Cl −, DIDS inhibited the basal Mg,ATPase activity and membrane potential formation. DIDS also inhibited the Cl −-stimulated ATPase activity and pH gradient formation. Direct inhibition of the electrogenic H +-ATPase by NO 3− or DIDS suggest that the vanadate-insensitive H +-pumping ATPase has anion-sensitive site(s) that regulate the catalytic and vectorial activity. Whether the anion-sensitive H +-ATPase has channels that conduct anions is yet to be established. 相似文献
14.
Soybeans ( Glycine max L. Merr., cv Kingsoy) were grown on media containing NO 3− or urea. The enrichments of shoots in K +, NO 3−, and total reduced N (N r), relative to that in Ca 2+, were compared to the ratios K +/Ca 2+,NO 3−/Ca 2+, and N r/Ca 2+ in the xylem saps, to estimate the cycling of K +, and N r. The net production of carboxylates (R −) was estimated from the difference between the sums of the main cations and inorganic anions. The estimate for shoots was compared to the theoretical production of R − associated with NO 3− assimilation in these organs, and the difference was attributed to export of R − to roots. The net exchange rates of H + and OH − between the medium and roots were monitored. The shoots were the site of more than 90% of total NO 3− reduction, and N r was cycling through the plants at a high rate. Alkalinization of the medium by NO 3−-fed plants was interrupted by stem girdling, and not restored by glucose addition to the medium. It was concluded that the majority of the base excreted in NO 3− medium originated from R − produced in the shoots, and transported to the roots together with K +. As expected, cycling of K + and reduced N was favoured by NO 3− nutrition as compared to urea nutrition. 相似文献
15.
The nature of the injury and recovery of nitrate uptake (net uptake) from NaCl stress in young barley ( Hordeum vulgare L, var CM 72) seedlings was investigated. Nitrate uptake was inhibited rapidly by NaCl, within 1 minute after exposure to 200 millimolar NaCl. The duration of exposure to saline conditions determined the time of recovery of NO 3− uptake from NaCl stress. Recovery was dependent on the presence of NO 3− and was inhibited by cycloheximide, 6-methylpurine, and cerulenin, respective inhibitors of protein, RNA, and sterol/fatty acid synthesis. These inhibitors also prevented the induction of the NO 3− uptake system in uninduced seedlings. Uninduced seedlings exhibited endogenous NO 3− transport activity that appeared to be constitutive. This constitutive activity was also inhibited by NaCl. Recovery of constitutive NO 3− uptake did not require the presence of NO 3−. 相似文献
16.
Current-voltage curves for DIDS-insensitive Cl − conductance have been determined in human red
blood cells from five donors. Currents were estimated from the rate of cell shrinkage using flow cytometry and differential laser light scattering. Membrane potentials were estimated from the extracellular pH of unbuffered suspensions using the proton ionophore FCCP. The width of the Gaussian distribution of cell volumes remained invariant during cell shrinkage, indicating a homogeneous Cl − conductance among the cells. After pretreatment for
30 min with DIDS, net effluxes of K + and Cl − were induced by valinomycin and were measured in the continued
presence of DIDS; inhibition was maximal at ∼65% above 1 μM DIDS at both 25°C and 37°C. The nonlinear current-voltage curves for DIDS-insensitive net Cl − effluxes, induced by valinomycin or gramicidin at varied [K +] o,
were compared with predictions based on ( 1) the theory of electrodiffusion, ( 2) a single barrier model, ( 3) single
occupancy, multiple barrier models, and ( 4) a voltage-gated mechanism. Electrodiffusion precisely describes the
relationship between the measured transmembrane voltage and [K +] o. Under our experimental conditions (pH
7.5, 23°C, 1–3 μM valinomycin or 60 ng/ml gramicidin, 1.2% hematocrit), the constant field permeability ratio
P K/P Cl is 74 ± 9 with 10 μM DIDS, corresponding to 73% inhibition of P Cl. Fitting the constant field current-voltage equation to the measured Cl − currents yields P
Cl = 0.13 h −1 with DIDS, compared to 0.49 h −1 without DIDS,
in good agreement with most previous studies. The inward rectifying DIDS-insensitive Cl − current, however, is inconsistent with electrodiffusion and with certain single-occupancy multiple barrier models. The data are well described either by a single barrier located near the center of the transmembrane electric field, or, alternatively, by a
voltage-gated channel mechanism according to which the maximal conductance is 0.055 ± 0.005 S/g Hb, half the
channels are open at −27 ± 2 mV, and the equivalent gating charge is −1.2 ± 0.3. 相似文献
17.
Short-term (10 minutes) measurements of plasmalemma NO 3− influx ( oc) into roots of intact barley plants were obtained using 13NO 3−. In plants grown for 4 days at various NO 3− levels (0.1, 0.2, 0.5 millimolar), oc was found to be independent of the level of NO 3− pretreatment. Similarly, pretreatment with Cl − had no effect upon plasmalemma 13NO 3− influx. Plants grown in the complete absence of 13NO 3− (in CaSO 4 solutions) subsequently revealed influx values which were more than 50% lower than for plants grown in NO 3−. Based upon the documented effects of NO 3− or Cl − pretreatments on net uptake of NO 3−, these observations suggest that negative feedback from vacuolar NO 3− and/or Cl − acts at the tonoplast but not at the plasmalemma. When included in the influx medium, 0.5 millimolar Cl − was without effect upon 13NO 3− influx, but NH 4+ caused approximately 50% reduction of influx at this concentration. 相似文献
18.
Experiments were designed to study the importance of organic acids as counterions for K + translocation in the xylem during excess cation uptake. A comparison was made of xylem exudate from wheat seedlings treated 72 hours with either 1.0 millimolar KNO 3 or 0.5 millimolar K 2SO 4, both in the presence of 0.2 millimolar CaSO 4. Exudation from KNO 3 plants had twice the volume and twice the K + and Ca 2+ fluxes or rate of delivery to shoots, as K 2SO 4 plants. Malate flux was 25% higher in K 2SO 4 than in KNO 3 exudate. Malate was the principal anion accompanying K + or Ca 2+ in K 2SO 4 treatment, while in the KNO 3 treatment, NO 3− was the principal anion. The contribution of SO 42− was negligible in both treatments. In a second experiment, exudate was collected every 4 hours during the daytime throughout a 72-hour treatment with KNO 3. Malate was the only anion present in exudate at first, just after the CaSO 4 pretreatment had ended. Malate concentration decreased and NO 3− concentration increased with time and these concentrations were negatively correlated. By 62 hours, NO 3− represented 80% of exudate anions. K + and NO 3− concentrations in exudate were strongly correlated with K + and NO 3− uptake, respectively. The first 36 hours of absorption from KNO 3 solution resembled the continuous absorption of K 2SO 4, in that malate was the principal counterion for translocation of K +. 相似文献
19.
Short-term ion uptake into roots of Limnobium stoloniferum was followed extracellularly with ion selective macroelectrodes. Cytosolic or vacuolar pH, together with the electrical membrane potential, was recorded with microelectrodes both located in the same young root hair. At the onset of chloride, phosphate, and nitrate uptake the membrane potential transiently decreased by 50 to 100 millivolts. During Cl − and H 2PO 4− uptake cytosolic pH decreased by 0.2 to 0.3 pH units. Nitrate induced cytosolic alkalinization by 0.19 pH units, indicating rapid reduction. The extracellular medium alkalinized when anion uptake exceeded K + uptake. During fusicoccin-dependent plasmalemma hyperpolarization, extracellular and cytosolic pH remained rather constant. Upon K + absorption, FC intensified extracellular acidification and intracellular alkalinization (from 0.31 to 0.4 pH units). In the presence of Cl − FC induced intracellular acidification. Since H + fluxes per se do not change the pH, recorded pH changes only result from fluxes of the stronger ions. The extra- and intracellular pH changes, together with membrane depolarization, exclude mechanisms as K +/A − symport or HCO 3−/A − antiport for anion uptake. Though not suitable to reveal the actual H +/A − stoichiometry, the results are consistent with an H +/A − cotransport mechanism. 相似文献
20.
The effect of exogenous NH 4+ on NO 3− uptake and in vivo NO 3− reductase activity (NRA) in roots of Phaseolus vulgaris L. cv Witte Krombek was studied before, during, and after the apparent induction of root NRA and NO 3− uptake. Pretreatment with NH 4Cl (0.15-50 millimolar) affected neither the time pattern nor the steady state rate of NO 3− uptake. When NH4+ was given at the start of NO3− nutrition, the time pattern of NO3− uptake was the same as in plants receiving no NH4+. After 6 hours, however, the NO3− uptake rate (NUR) and root NRA were inhibited by NH4+ to a maximum of 45% and 60%, respectively. The response of the NUR of NO3−-induced plants depended on the NH4Cl concentration. Below 1 millimolar NH4+, the NUR declined immediately and some restoration occurred in the second hour. In the third hour, the NUR became constant. In contrast, NH4+ at 2 millimolar and above caused a rapid and transient stimulation of NO3− uptake, followed again by a decrease in the first, a recovery in the second, and a steady state in the third hour. Maximal inhibition of steady state NUR was 50%. With NO3−-induced plants, root NRA responded less and more slowly to NH4+ than did NUR. Methionine sulfoximine and azaserine, inhibitors of glutamine synthetase and glutamate synthase, respectively, relieved the NH4+ inhibition of the NUR of NO3−-induced plants. We conclude that repression of the NUR by NH4+ depends on NH4+ assimilation. The repression by NH4+ was least at the lowest and highest NH4+ levels tested (0.04 and 25 millimolar). 相似文献
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