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1.
Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as NO 3− or NH 4+, the solutions being maintained at pH 5.5. In NO 3−-fed plants excess nutrient anion over cation uptake was equivalent to net OH − efflux, and the total charge from NO 3− and SO 42− reduction equated to the sum of organic anion accumulation plus net OH − efflux. In NH 4+-fed plants a large H + efflux was recorded in close agreement with excess cation over anion uptake. This H + efflux equated to the sum of net cation (NH 4+ minus SO 42−) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO 3− that is taken up and reduced in NO 3−-fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH 4+-fed plants absorbed NH 4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO 3−-fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake, assimilation, and accumulation data in terms of shoot/root pH regulation and cycling of nutrients. 相似文献
2.
Supplying both N forms (NH 4
++NO 3
−) to the maize ( Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible
for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore,
field and gravel hydroponic studies were conducted to examine the effect of N form (NH 4
++NO 3
− versus predominantly NO 3
−) and exogenous cytokinin treatment (six foliar applications of 22 μ M 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants,
NH 4
++NO 3
− nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO 3
−. Cytokinin application to NO 3
−-grown field plants increased grain yield to that of NH 4
++NO 3
−-grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise,
hydroponically grown maize supplied with NH 4
++NO 3
− doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH 4
++NO 3
− nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH 4
++NO 3
− plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO 3
−-grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH 4
++NO 3
− may be partly associated with an increased endogenous cytokinin supply. 相似文献
3.
Phosphate-limited chemostat cultures were used to study cell growth and N assimilation in Anabaena flos-aquae under various N sources to determine the relative energetic costs associated with the assimilation of NH 3, NO 3−, or N 2. Expressed as a function of relative growth rate, steady state cellular P contents and PO 4 assimilation rates did not vary with N-source. However, N-source did alter the maximal PO 4-limited growth rate achieved by the cultures: the NO 3− and N 2 cultures attained only 97 and 80%, respectively, of the maximal growth rate of the NH 3 grown cells. Cellular biomass and C contents did not vary with growth rate, but changed with N source. The NO 3−-grown cells were the smallest (627 ± 34 micromoles C · 10 −9 cells), while NH 3-grown cells were largest (900 ± 44 micromoles C · 10 −9 cells) and N 2-fixing cells were intermediate (726 ± 48 micromoles C · 10 −9 cells) in size. In the NO 3−-and N 2-grown cultures, N content per cell was only 57 and 63%, respectively, of that in the NH 3-grown cells. Heterocysts were absent in NH 3-grown cultures but were present in both the N 2 and NO 3− cultures. In the NO 3−-grown cultures C 2H 2 reduction was detected only at high growth rates, where it was estimated to account for a maximum of 6% of the N assimilated. In the N 2-fixing cultures the acetylene:N 2 ratio varied from 3.4:1 at lower growth rates to 3.0:1 at growth rates approaching maximal. Compared with NH3, the assimilation of NO3− and N2 resulted either in a decrease in cellular C (NO3− and N2 cultures) or in a lower maximal growth rate (N2 culture only). The observed changes in cell C content were used to calculate the net cost (in electron pair equivalents) associated with growth on NO3− or N2 compared with NH3. 相似文献
4.
We examined nitrate assimilation and root gas fluxes in a wild-type barley ( Hordeum vulgare L. cv Steptoe), a mutant ( nar1a) deficient in NADH nitrate reductase, and a mutant ( nar1a; nar7w) deficient in both NADH and NAD(P)H nitrate reductases. Estimates of in vivo nitrate assimilation from excised roots and whole plants indicated that the nar1a mutation influences assimilation only in the shoot and that exposure to NO 3− induced shoot nitrate reduction more slowly than root nitrate reduction in all three genotypes. When plants that had been deprived of nitrogen for several days were exposed to ammonium, root carbon dioxide evolution and oxygen consumption increased markedly, but respiratory quotient—the ratio of carbon dioxide evolved to oxygen consumed—did not change. A shift from ammonium to nitrate nutrition stimulated root carbon dioxide evolution slightly and inhibited oxygen consumption in the wild type and nar1a mutant, but had negligible effects on root gas fluxes in the nar1a; nar7w mutant. These results indicate that, under NH 4+ nutrition, 14% of root carbon catabolism is coupled to NH 4+ absorption and assimilation and that, under NO 3− nutrition, 5% of root carbon catabolism is coupled to NO 3− absorption, 15% to NO 3− assimilation, and 3% to NH 4+ assimilation. The additional energy requirements of NO 3− assimilation appear to diminish root mitochondrial electron transport. Thus, the energy requirements of NH 4+ and NO 3− absorption and assimilation constitute a significant portion of root respiration. 相似文献
5.
Assimilation of NO 3− and NH 4+ by perennial ryegrass ( Lolium perenne L.) turf, previously deprived of N for 7 days, was examined. Nitrogen uptake rate was increased up to four- to five-fold for both forms of N by N-deprivation as compared to N-sufficient controls, with the deficiency-enhanced N absorption persisting through a 48 hour uptake period. Nitrate, but not NH 4+, accumulated in the roots and to a lesser degree in shoots. By 48 hours, 53% of the absorbed NO 3− had been reduced, whereas 97% of the NH 4+ had been assimilated. During the early stages (0 to 8 hours) of NO 3− uptake by N-deficient turf, reduction occurred primarily in the roots. Between 8 and 16 hours, however, the site of reduction shifted to the shoots. Nitrogen form did not affect partitioning of the absorbed N between roots (40%) and shoots (60%) but did affect growth. Compared to NO 3−, NH 4+ uptake inhibited root, but not shoot, growth. Total soluble carbohydrates decreased in both roots and shoots during the uptake period, principally the result of fructan metabolism. Ammonium uptake resulted in greater total depletion of soluble carbohydrates in the root compared to NO 3− uptake. The data indicate that N assimilation by ryegrass turf utilizes stored sugars but is also dependent on current photosynthate. 相似文献
6.
At root temperature below 14 C the absorption of 15N from NH 4+ greatly exceeded that from NO 2− by tillers of Lolium multiflorum and Lolium perenne under conditions where pH, external concentration, plant N status, and pretreatment temperature were varied. There was a marked increase in the temperature sensitivity of NO 3− transport below 14 C, irrespective of the temperature at which plants were grown previously. A marked increase in the temperature sensitivity was also seen for NH 4+ transport, but this occurred at the lower temperature of 10 C. Pretreatment of roots at 8 C lowered this still further to 5 C. Above and below these transition temperatures the Q 10 values for NO 3− and NH 4+ transport were similar. Thus, the increased absorption of NH 4+ relative to NO 3− at low temperatures seems to be related primarily to the difference in transition temperatures. 相似文献
7.
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
8.
We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO 3
−), ammonium (NH 4
+), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L −1 for NO 3
− and NH 4
+, 0.5–50 μmol N L −1 for urea, 0.5–100 μmol N L −1 for glu and cyanate, and 0.5–200 μmol N L −1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μ m, 1.51±0.06 d −1 and 1.50±0.05 d −1, respectively). However, cultures grown on cyanate, NO 3
−, and NH 4
+ had lower half saturation constants (K μ, 0.28–0.51 μmol N L −1). N uptake kinetics were measured in NO 3
−-deplete and -replete batch cultures of P. donghaiense. In NO 3
−-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO 3
−, NH 4
+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L −1. In NO 3
−-replete batch cultures, NH 4
+, urea, and algal amino acid uptake kinetics were similar to those measured in NO 3
−-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth. 相似文献
9.
In Mucuna pruriens var. utilis, grown with nitrate-N in a hydroponic split-root system, an Al avoidance reaction of root growth was observed, which was ascribed to local P stress in the Al containing compartment. The Al avoidance reaction was similar to the avoidance of Mucuna roots of acid subsoil in the field where roots grew preferentially in the topsoil. In the present paper the effect of different N forms (NO 3
– and NH 4
+) on the reactions of Mucuna to Al were studied, since in acid soils N is present as a mixture of NO 3
– and NH 4
+. No interaction between the N form and Al toxicity was found. A hydroponic split-root experiment with NH 4NO 3 nutrition, which is comparable to the situation in the field, showed that under these conditions Al avoidance did not occur. It is concluded that a relation between the Al avoidance reaction of Mucuna and P stress is still likely.Abbreviations D r
root diameter
- L pr
total root length per plant
- L rw
specific root length
- NRA
nitrate reductase activity
- S/R
shoot: root ratio 相似文献
10.
Nitrogen-14 and nitrogen-15 nuclear magnetic resonance (NMR) spectra were recorded for freshly dissected buds of Picea glauca and for buds grown for 3, 6 and 9 weeks on shoot-forming medium. Resonances for Glu (and other αNH 2 groups), Pro, Ala, and the side chain groups in Gln, Arg, Orn, and γ-aminobutyric acid could be detected in in vivo15N NMR spectra. Peaks for α-amino groups, Pro, NO 3− and NH 4+ could also be identified in 14N NMR spectra. Perfusion experiments performed for up to 20 hours in the NMR spectrometer showed that 15N-labeled NH 4+ and NO 3− are first incorporated into the amide group of Gln and then in the αNH 2 pool. Subsequently, it also emerges in Ala and Arg. These data suggest that the glutamine synthetase/ glutamate synthase pathway functions under these conditions. The assimilation of NH 4+ is much faster than that of NO 3−. Consequently after 10 days of growth more than 70% of the newly synthesized internal free amino acid pool derives its nitrogen from NH 4+ rather than NO 3−. If NH 4+ is omitted from the medium, no NO 3− is taken up during 9 weeks and the buds support limited growth by utilizing their endogenous amino acid pools. It is concluded that NH 4+ and NO 3− are both required for the induction of nitrate- and nitrite reductase. 相似文献
11.
Chlamydomonas reinhardii cells, growing photoautotrophically under air, excreted to the culture medium much higher amounts of NO 2− and NH 4+ under blue than under red light. Under similar conditions, but with NO 2− as the only nitrogen source, the cells consumed NO 2− and excreted NH 4+ at similar rates under blue and red light. In the presence of NO 3− and air with 2% CO 2 (v/v), no excretion of NO 2− and NH 4+ occurred and, moreover, if the bubbling air of the cells that were currently excreting NO 2− and NH 4+ was enriched with 2% CO 2 (v/v), the previously excreted reduced nitrogen ions were rapidly reassimilated. The levels of total nitrate reductase and active nitrate reductase increased several times in the blue-light-irradiated cells growing on NO 3− under air. When tungstate replaced molybdate in the medium (conditions that do not allow the formation of functional nitrate reductase), blue light activated most of the preformed inactive enzyme of the cells. Furthermore, nitrate reductase extracted from the cells in its inactive form was readily activated in vitro by blue light. It appears that under high irradiance (90 w m −2) and low CO 2 tensions, cells growing on NO 3− or NO 2− may not have sufficient carbon skeletons to incorporate all the photogenerated NH 4+. Because these cells should have high levels of reducing power, they might use NO 3− or, in its absence, NO 2− as terminal electron acceptors. The excretion of the products of NO 2− and NH 4+ to the medium may provide a mechanism to control reductant level in the cells. Blue light is suggested as an important regulatory factor of this photorespiratory consumption of NO 3− and possibly of the whole nitrogen metabolism in green algae. 相似文献
12.
The effect of nitrogen form (NH 4-N, NH 4-N + NO 3−, NO 3−) on nitrate reductase activity in roots and shoots of maize ( Zea mays L. cv INRA 508) seedlings was studied. Nitrate reductase activity in leaves was consistent with the well known fact that NO 3− increases, and NH 4+ and amide-N decrease, nitrate reductase activity. Nitrate reductase activity in the roots, however, could not be explained by the root content of NO 3−, NH 4-N, and amide-N. In roots, nitrate reductase activity in vitro was correlated with the rate of nitrate reduction in vivo. Inasmuch as nitrate reduction results in the production of OH − and stimulates the synthesis of organic anions, it was postulated that nitrate reductase activity of roots is stimulated by the released OH − or by the synthesized organic anions rather than by nitrate itself. Addition of HCO 3− to nutrient solution of maize seedlings resulted in a significant increase of the nitrate reductase activity in the roots. As HCO 3−, like OH −, increases pH and promotes the synthesis of organic anions, this provides circumstantial evidence that alkaline conditions and/or organic anions have a more direct impact on nitrate reductase activity than do NO 3−, NH 4-N, and amide-N. 相似文献
13.
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
14.
Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH 4 or NO3 at 10 mmol m ?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO 3. The specific absorption rate (SAR) of NH +4 was greater at all temperatures than SAR-NO 3. In plants grown with NH +, 3–5% of the total N was recovered as NH +4, whereas in those grown with NO ?3 the unassimilated NO ?3 rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH +4 lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO ?3-grown plants. Plants grown with NH +4 had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO ?3 grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH +4 or NO ?3. The additional residual N (protein) in NH +4 grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient. 相似文献
15.
Young bean plants ( Phaseolus vulgaris L. var Saxa) were fed with 3.5 or 10 millimolar N in either the form of NO 3− or NH 4+, after being grown on N-free nutrient solution for 8 days. The pH of the nutrient solutions was either 6 or 4. The cell sap pH and the extractable activities of phosphoenolpyruvate carboxylase and of pyruvate kinase from roots and primary leaves were measured over several days. The extractable activity of phosphoenolpyruvate carboxylase (based on soluble protein) from primary leaves increased with NO3− nutrition, whereas with NH4+ nutrition and on N-free nutrient solution the activity remained at a low level. Phosphoenopyruvate carboxylase activity from the roots of NH4+-fed plants at pH 4 was finally somewhat higher than from the roots of plants grown on NO3− at the same pH. There was no difference in activity from the root between the N treatments when pH in the nutrient solutions was 6. The extractable activity of pyruvate kinase from roots and primary leaves seemed not to be influenced by the N nutrition of the plants. The results are discussed in relation to the physiological function of both enzymes with special regard to the postulated functions of phosphoenolpyruvate carboxylase in C3 plants as an anaplerotic enzyme and as part of a cellular pH stat. 相似文献
16.
Many reports have shown that plant growth and yield is superior on mixtures of NO 3− and NH 4+ compared with provision of either N source alone. Despite its clear practical importance, the nature of this N-source synergism at the cellular level is poorly understood. In the present study we have used the technique of compartmental analysis by efflux and the radiotracer 13N to measure cellular turnover kinetics, patterns of flux partitioning, and cytosolic pool sizes of both NO 3− and NH 4+ in seedling roots of rice ( Oryza sativa L. cv IR72), supplied simultaneously with the two N sources. We show that plasma membrane fluxes for NH 4+, cytosolic NH 4+ accumulation, and NH 4+ metabolism are enhanced by the presence of NO 3−, whereas NO 3− fluxes, accumulation, and metabolism are strongly repressed by NH 4+. However, net N acquisition and N translocation to the shoot with dual N-source provision are substantially larger than when NO 3− or NH 4+ is provided alone at identical N concentrations. 相似文献
17.
A study was conducted to elucidate the effect of N form, either NH 4
+ or NO 3
–, on growth and solute composition of the salt-tolerant kallar grass [ Leptochloa fusca (L.) Kunth] grown under 10 m M or 100 m M NaCl in hydroponics. Shoot biomass was not affected by N form, whereas NH 4
+ compared to NO 3
– nutrition caused an almost 4-fold reduction in the root biomass at both salinity levels. Under NH 4
+ nutrition, salinity had no effect on the biomass yield, whereas under NO 3
– nutrition, increasing salinity from 10 m M to 100 m M caused 23% and 36% reduction in the root and shoot biomass, respectively. The reduced root growth under NH 4
+ nutrition was not attributable to impaired shoot to root C allocation since N form did not affect the overall root sugar concentration and the starch concentration was even higher under NH 4
+ compared to NO 3
– nutrition. The low NH 4
+ (2 m M) and generally higher amino-N concentrations in NH 4
+- compared to NO 3
–-fed plants indicated that the grass was able to effectively detoxify NH 4
+. Salinity had no effect on Ca 2+ and Mg 2+ levels, whereas their concentration in shoots was lower under NH 4
+ compared to NO 3
– nutrition (over 66% reduction in Ca 2+; over 20% reduction in Mg 2+), but without showing deficiency symptoms. Ammonium compared to NO 3
– nutrition did not inhibit K + uptake, and the K +-Na + selectivity either remained unaffected or it was higher under NH 4
+ than under NO 3
– nutrition. Results suggested that while NH 4
+
versus NO 3
– nutrition substantially reduced root growth, and also strongly modified anion concentrations and to a minor extent concentrations of divalent cations in shoots, it did not influence salt tolerance of kallar grass. 相似文献
18.
Biochar produced by pyrolysis of biomass can be used to counter nitrogen (N) pollution. The present study investigated the effects of feedstock and temperature on characteristics of biochars and their adsorption ability for ammonium N (NH 4
+-N) and nitrate N (NO 3
−-N). Twelve biochars were produced from wheat-straw (W-BC), corn-straw (C-BC) and peanut-shell (P-BC) at pyrolysis temperatures of 400, 500, 600 and 700°C. Biochar physical and chemical properties were determined and the biochars were used for N sorption experiments. The results showed that biochar yield and contents of N, hydrogen and oxygen decreased as pyrolysis temperature increased from 400°C to 700°C, whereas contents of ash, pH and carbon increased with greater pyrolysis temperature. All biochars could sorb substantial amounts of NH 4
+-N, and the sorption characteristics were well fitted to the Freundlich isotherm model. The ability of biochars to adsorb NH 4
+-N followed: C-BC>P-BC>W-BC, and the adsorption amount decreased with higher pyrolysis temperature. The ability of C-BC to sorb NH 4
+-N was the highest because it had the largest cation exchange capacity (CEC) among all biochars (e.g., C-BC400 with a CEC of 38.3 cmol kg −1 adsorbed 2.3 mg NH 4
+-N g −1 in solutions with 50 mg NH 4
+ L −1). Compared with NH 4
+-N, none of NO 3
−-N was adsorbed to biochars at different NO 3
− concentrations. Instead, some NO 3
−-N was even released from the biochar materials. We conclude that biochars can be used under conditions where NH 4
+-N (or NH 3) pollution is a concern, but further research is needed in terms of applying biochars to reduce NO 3
−-N pollution. 相似文献
19.
Either NO 3− (16 millimolar) or NH 4+ (1 millimolar) completely inhibited infection and nodulation of white clover seedlings ( Trifoliin repens) inoculated with Rhizobium trifolii. The binding of R. trifolii to root hairs and the immunologically detectable levels of the plant lectin, trifoliin, on the root hair surface had parallel declining slopes as the concentration of either NO 3− or NH 4+ was increased in the rooting medium. This supports the role of trifoliin in binding R. trifolii to clover root hairs. Agglutination of R. trifolii by trifoliin from seeds was not inhibited by these levels of NO 3− or NH 4+. The results suggest that these fixed N ions may play important roles in regulating an early recognition process in the Rhizobium-clover symbiosis, namely the accumulation of high numbers of infective R. trifolii cells on clover root hairs. 相似文献
20.
Ammonium (NH 4+) nutrition inhibits water uptake and root exudation and decreases leaf water potential of tomato plants grown in solution culture. This inhibition is readily reversible by NO 3− for short term exposures to NH 4+; however, recovery is delayed following long term exposures. 相似文献
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