Carbohydrate and lipid status in soybean roots influenced by ferulic acid uptake

The objective of this research was to investigate how the allelochemical ferulic acid affects the carbohydrate and lipid contents of soybean roots cultivated in nutrient culture. The results presented revealed that ferulic acid has significant effects on carbohydrates by the increase in xylose, fructose and sucrose and decrease in glucose, after 24 h treatment of roots. Ferulic acid increased the contents of saturated and unsaturated fatty acids of the polar and non-polar lipid fractions. The results may contribute as additional data to explain allelopathic effects caused by ferulic acid.     

Cyclic variations in nitrogen uptake rate of soybean plants: effects of pH and mixed nitrogen sources.

To determine if the daily pattern of NO3- and NH4+ uptake is affected by acidity or NO3- : NH4+ ratio of the nutrient solution, non-nodulated soybean plants (Glycine max) were exposed for 21 days to replenished, complete nutrient solutions at pH 6.0, 5.5, 5.0, and 4.5 which contained either 1.0 mM NH4+, 1.0 mM NO3- [correction of NO3+], 0.67 mM NH4+ plus 0.33 mM NO3- (2:1 NH4+ : NO3-) [correction of (2:1 NH3+ : NO4-)], or 0.33 mM NH4+ plus 0.67 mM NO3- (1:2 NH4+ : NO3-). Net uptake rates of NH4+ and NO3- were measured daily by ion chromatography as depletion from the replenished solutions. When NH4+ and NO3- were supplied together, cumulative uptake of total nitrogen was not affected by pH or solution NH4+ : NO3- ratio. The cumulative proportion of nitrogen absorbed as NH4+ decreased with increasing acidity; however, the proportional uptake of NH4+ and NO3- was not constant, but varied day-to-day. This day-to-day variation in relative proportions of NH4+ and NO3- absorbed when NH4+ : NO3- ratio and pH of solution were constant indicates that the regulatory mechanism is not directly competitive. Regardless of the effect of pH on cumulative uptake of NH4+, the specific nitrogen uptake rates from mixed and from individual NH4+ and NO3- sources oscillated between maxima and minima at each pH with average periodicities similar to the expected interval of leaf emergence.     

The effect of soil acidification on atmospheric methane uptake by a Maine forest soil(1)

Soil from the zone of maximal methanotrophic activity (approximately 5-8 cm depth) in a mixed coniferous-hardwood forest consumed atmospheric methane over a wide pH range (3.5-7.5) with a broad optimum between 4.8 and 6.0. Methane uptake at native soil pH values (4.4-4.8) was only slightly less rapid than rates at optimal pH values. Addition of mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption. The extent of inhibition varied with the type, concentration and volume of acid added: nitric acid was more inhibitory than sulfuric acid at an equivalent soil pH, and methane uptake decreased with increasing volumes and concentrations of added acid. Although ammonium chloride at 1 μmol g fresh weight (gfw) soil(-1) inhibited methane uptake, the extent of inhibition did not vary significantly with decreasing soil pH below values of 4.4.     

Effects of ferulic acid on L-malate oxidation in isolated soybean mitochondria

The effects of ferulic acid on L-malate oxidation in mitochondria isolated from soybean (Glycine max L.) seedlings were investigated. Oxygen uptake and the products of L-malate oxidation were measured under two conditions: pH 6.8 and 7.8. At acidic pH, the activity of the NAD+-linked malic enzyme (L-malate:NAD+oxidoreductase [decarboxylating] EC 1.1.1.39) was favoured, whereas at alkaline pH a predominance of the L-malate dehydrogenase activity (L-malate:NAD+oxidoreductase EC 1.1.1.37) was apparent. Ferulic acid inhibited basal and coupled respiration during L-malate oxidation either at acidic or alkaline pH, reducing also the amounts of pyruvate or oxaloacetate produced. The results suggest that the site of ferulic acid action is situated at some step that precedes the respiratory chain. An interference with the L-malate entry into the mitochondria could be an explanation for the effects of ferulic acid, but the possibility of a direct inhibition of both enzymes involved in L-malate oxidation cannot be ruled out. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inorganic carbon acquisition in the acid‐tolerant alga Chlorella kessleri

The ability of the freshwater alga, Chlorella kessleri, to maintain a carbon concentrating mechanism when grown at acid pH was investigated. The alga grows over the pH range 4.0–9.0 and was found to take up bicarbonate and CO₂ actively when grown at pH 6.0. However, when grown at acid pH (below 5.5), it does not have active CO₂ uptake. The acidotolerant species maintained an internal pH of 6.1–7.5 over the external pH range 4.5–7.5, thus the pH difference between the cell interior and the external medium was large enough to allow for the diffusive uptake of CO₂ at acid external pH. Mass spectrometric monitoring of O₂ and CO₂ fluxes by suspensions of C. kessleri, grown at acid pH, and maintained at pH 7.5 showed that the rates of O₂ evolution did not exceed those of CO₂ uptake. The final CO₂ compensation concentrations of 14.0–17.7 µM reached by photosynthetic cells were above the CO₂ equilibrium concentration in the external medium, indicating a lack of active CO₂ uptake at acid pH. Chlorella kessleri accumulated CO₂ with internal concentrations that were 9.9, 18.7 and 22.7‐fold that of the external medium for cells grown, respectively, at pH 4.5, 5.0 and 5.5. The ability of C. kessleri cells to accumulate high intracellular concentrations of inorganic carbon at acid pH would provide a sufficiently high concentration of CO₂ at the active site of Rubisco thus allowing the alga to maintain growth rates similar to those at alkaline pH.     

A comparative study of ammonium toxicity at different constatn pH of the nutrient solution

Seedlings of 14 species were grown for 14–28 days on nutrient solution with 6 mmol.l⁻¹ NH₄ as the sole nitrogen source. Solutions acidity was were kept constant at pH 4.0, 5.0, 6.0 and 7.0 by continuous titration with diluted KOH. The following species were used: barley, maize, oats sorghum, yellow and white lupin, pea, soybean, carrot, flax, castor-oil, spinach, sugarbeet and sunflower. Most plant species grew optimally at pH 6.0 with slight reductions at pH 5.0. Growth of many species was severely inhibited at pH 4.0, but this inhibition was not observed with the legume and cereal species. Yield depressions at pH 4.0 relative to pH 6.0 were well correlated with the respective relative decreases of the K concentration in their roots (P<0.002). In the roots of two species (sunflower and flax) total N concentrations were also strongly reduced at pH 4.0. apparently, the interactions between uptake of K, NH₄ and H ions become the prevalent problem at suboptimal pH. At pH 7.0, yields were also considerably decreased, with the exception of the lupines. At this pH, the roots of the growth inhibited plants were characterized by increased levels of total N and free NH₄. It is thought that the binding capacity of the roots for NH₄ is an important factor in preventing NH₄/NH₃ toxicity at supraoptimal pH.     

Growth and nutrient uptake of sorghum cultivated with vesicular-arbuscular mycorrhiza isolates at varying pH

This study was conducted to determine the effects of different pH regimes on root colonization with four vesicular-arbuscular mycorrhiza (VAM) isolates, and VAM effects on host plant growth and nutrient uptake. Sorghum [Sorghum bicolor (L.) Moench] was grown at pH 4.0, 5.0, 6.0 and 7.0 (±0.1) in hydroponic sand culture with the VAM isolates Glomus etunicatum UT316 (isolate E), G. intraradices UT143 (isolate I), G. intraradices UT126 (isolate B), and an unknown Glomus isolate with no INVAM number (isolate A). Colonization of roots with the different VAM isolates varied differentially with pH. As pH increased, root colonization increased with isolates B and E, remained unchanged with isolate I, and was low at pH 4.0 and high at pH 5.0, 6.0, and 7.0 with isolate A. Isolates E and I were more effective than isolates A and B in promoting plant growth irrespective of pH. Root colonization with VAM appeared to be independent of dry matter yields or dry matter yield responsiveness (dry matter produced by VAM compared to nonmycorrhizal plants). Dry matter yield responsiveness values were higher in plants whose roots were colonized with isolates E and I than with isolates A and B. Shoot P concentrations were lower in plants colonized with isolates E and I than with isolates A and B or nonmycorrhizal plants. This was probably due to the dilution effect of the higher dry matter yields. Neither the VAM isolate nor pH had an effect on shoot Ca, Mg, Zn, Cu, and Mn concentrations, while the VAM isolate affected not only P but also S, K, and Fe concentrations. The pH x VAM interaction was significant for shoot K, Mg, and Cu concentrations.     

The influence of pH on cystine and dibasic amino acid transport by rat renal brushborder membrane vesicles

The uptake of cystine and lysine by rat renal brushborder membrane vesicles was examined at various intravesicular and extravesicular hydrogen ion concentrations to discern whether ionic species are determinants of specificity for the shared transport system and whether hydrogen ion gradients play a role in determining uptake values. When intravesicular and extravesicular pH are identical, the highest uptake of cystine occurred at pH 7.4, with lesser uptake at pH 6.0 and 8.3. Since cystine is electroneutral at pH 6.0 and 90% anionic at pH 8.3, it appears that neither form of the amino acid is a preferred species for transport. A similar relationship between pH and uptake occurs for lysine, which is cationic at pH below 8.5. This suggests that pH affects the functioning of the membrane carrier system independent of ionic species of the substrate. There is no apparent relationship of cystine uptake to hydrogen ion gradients across the membrane. Over the range of extravesicular pH studied, optimal cystine uptake occurred whenever the intravesicular pH was 7.4. Competitive interactions between unlabeled amino acids and labeled cystine were not affected by the extravesicular pH and, therefore, did not seem determined by the ionic species of cystine.     

Growth and physiological responses of trembling aspen (Populus tremuloides), white spruce (Picea glauca) and tamarack (Larix laricina) seedlings to root zone pH

Background and aims

Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH.

Methods

In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0.

Results

The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH.

Conclusions

The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth.     

Humic acid and iron uptake by plants

Summary The behaviour of ferric EDTA and ferric citrate in nutrient solution and their interaction with humic acid was investigated at various hydrogen ion concentrations using the technique of membrane ultrafiltration to separate small iron species from high molecular weight products of hydrolysis and to estimate the binding of iron by humic acid. Ferric EDTA was found to be of small molecular size at all pH values between 5.0 and 7.0 whilst ferric citrate solutions contained an increasing proportion of high molecular weight material as pH was increased from 5.0 to 7.0. Some iron present in solutions of both ferric EDTA and ferric citrate was bound by humic acid at all pH values from 5.0 to 7.0. Studies were also made of the uptake of iron by wheat roots from nutrient solutions containing either ferric EDTA or ferric citrate and of the effect of humic acid on uptake. More iron was absorbed from ferric EDTA than from ferric citrate at all pH values. Increasing pH between 5.0 and 7.0 resulted in a progressive decrease in the uptake of iron in both cases. The presence of humic acid depressed iron absorption from both solutions at all pH values.     

Quantitative evaluation of the role of organic acid exudation in the mobilization of rock phosphate by rape

Phosphorus-deficient rape plants appear to acidify part of their rhizosphere by exuding malic and citric acid. A simulation model was used to evaluate the effect of measured exudation rates on phosphate uptake from Mali rock phosphate. The model used was one on nutrient uptake, extended to include both the effect of ion uptake and exudation on rhizosphere pH and the effect of rhizosphere pH on the solubilization of rock phosphate. Only the youngest zones of the root system were assumed to exude organic acids. The transport of protons released by organic acids was described by mass flow and diffusion. An experimentally determined relation was used describing pH and phosphate concentration in the soil solution as a function of total soil acid concentration. Model parameters were determined in experiments on organic acid exudation and on the uptake of phosphate by rape from a mixture of quartz sand and rock phosphate. Results based on simulation calculations indicated that the exudation rates measured in rape plants deficient in phosphorus can provide the roots with more phosphate than is actually taken up. Presence of root hairs enhanced the effect of organic acid exudation on calculated phosphate uptake. However, increase of root hair length without exudation as an alternative strategy to increase phosphate uptake from rock phosphate appeared to be less effective than exudation of organic acids. It was concluded that organic acid exudation is a highly effective strategy to increase phosphate uptake from rock phosphate, and that it unlikely that other rhizosphere processes play an important role in rock phosphate mobilization by rape.     

Oscillatory behavior of Saccharomyces cerevisiae in continuous culture: II. Analysis of cell synchronization and metabolism

Sustained oscillations of biomass, ethanol, and ammonium concentrations, specific growth rate, and specific uptake rates of ethanol, ammonium, and oxygen were found in continuous cultures of Saccharomyces cerevisiae under controlled dissolved oxygen (DO), pH, and temperature conditions. The period of oscillations was approximately 2.5-3 h at a pH of 5.5 and 2-2.5 h at a pH of 6.5. Oscillations were observed only under conditions of low carbon (glucose below the minimum detectable level), nitrogen nutrient (ammonium concentration varied between 0.00001 and 0.0015M), and ethanol concentration (0.002-0.085 g/L) in the bioreactor.The oscillatory behavior at pH 5.5 was also characterized by partially synchronized cell growth and reproduction. Not only did the total percentage of budding cells oscillate with the same period as observed for the global biomass and nutrient concentrations, but the peaks in the individual subpopulations of initial budding, middle budding, and late budding cells appeared sequentially during the oscillation period. This provides strong evidence of the hypothesis that variations in metabolism during different periods in the cell cycle of a partially synchronized cell population are responsible for the observed oscillatory bioreactor behavior.The specific nutrient uptake rates for ammonium and oxygen as well as the net specific ethanol uptake rate oscillated with the same period as the biomass oscillations. These results show a dramatic increase in the ammonium and oxygen consumption rates prior to the initial budding of the synchronized subpopulation and a decrease in these rates during the late budding phase. At a pH of 5.5, the late budding phase is characterized by high specific ethanol productivity; however, the ethanol productivity lags the late budding phase at a pH pf 6.5. The observed time-varying metabolism in the oscillatory operating regime appears to be the result of the metabolic changes which occur during the cell cycle. Models which can predict the oscillatory biomass concentration and nutrient levels in this regime must be capable of predicting the concentrations and metabolic rates of the subpopulations as well.     

The influence of phosphate nutrition on H ion efflux from the roots of young rape plants

Changes in pH around the roots of young rape plants were studied using a nutrient film technique which allowed either part or all of the root system to be subjected to specific nutrient treatments. The rapidity and direction of change of pH was assessed by embedding absorbing roots in a thin layer of agar containing bromocresol purple. Measurements were also made with a pH microelectrode placed next to the roots. Phosphate-fed plants were deprived of phosphate when 14 days old. Patterns of pH changes round the deprived roots were the same as with phosphate-fed plants until the plants had been deprived of P for three days, when H ion efflux started in the terminal portions of the roots. The lengths of root producing acid and amounts of H ion both increased as the plants became more P deficient. Both P fed and P deprived roots produced HCO₃ ions but the net amount of HCO₃ ion produced by the P deficient roots fell as did nitrate uptake rates. Cation-anion balances measured at the end of the experiment showed that uptake of all anions and K decreased in the P deprived plants but uptake of Ca and Mg were little altered. This resulted in a smaller ratio of anions to cations absorbed which was reflected in the reduced HCO₃ ion efflux.     

Acid soil damage in sorghum genotypes: Role of magnesium deficiency and root impairment

The effects of liming and Mg fertilization on growth, specific root length (root length per unit of root dry weight; SRL) and nutrient uptake of twelve sorghum genotypes (Sorghum bicolor (L.) Moench) were studied in two pot experiments. Liming increased the pH of the sandy loam from pH 4.3 (unlimed) to 4.7 (with 0.5 g Ca(OH)₂ kg^-1 soil) and to 6.1 (with 2.5 g Ca(OH)₂ kg^-1 soil). Liming increased the dry matter yield of the genotypes by factors of 1.2 to 6.0 (between pH 4.3 and 4.7) and by 1.1 to 2.4 (between pH 4.7 and 6.1). In absence of Mg at soil pH of 4.3 and 4.7, all genotypes suffered from Mg deficiency, as indicated by low Mg concentrations in the shoots (26–94 mmol Mg kg^-1 DM) and visible Mg deficiency symptoms. At pH 4.7 several of the genotypes responded to Mg application and produced significantly more dry matter. At pH 4.3, however, none of the genotypes responded to Mg, even though the internal Mg concentrations were increased by applied Mg. The relative increase in dry matter yield between pH 4.3 and 4.7 was closely correlated to the relative change in specific root length in the same soil pH interval, especially when the soil was fertilized with Mg (r²=0.91^**). The group of genotypes where SRL and dry matter yield were reduced by soil acidity was not the same as the group that responded positively to Mg application at pH 4.7.It is concluded that the growth of sorghum genotypes on acid soils is determined by two independent characteristics: the sensitivity of root development to soil acidity and the efficiency of the uptake and utilization of Mg. The first characteristic is predminant at high soil acidity whilst the latter is dominant at moderate soil acidity.     

Macronutrient concentrations of soybean infected with soybean cyst nematode

Soybean cultivars (Glycine max(L.) Merr.) infected with soybean cyst nematode (SCN; Heterodera glycinesIchinohe) often show symptoms similar to K deficiency. The objectives of this experiment were to determine if SCN infection affected macronutrient concentrations in soybean seedling vegetative tissues, determine whether increased K fertility can overcome these possible effects, and to determine if these possible effects are localized at the site of infection or expressed systemically throughout the root system. Soybean plants were grown with root systems split into two halves. This allowed differential K (0.2, 2.4 and 6.0 mM K nutrient solutions) and SCN (0 and 15 000 eggs/plant) treatments to be applied to opposite root-halves of the same plant. Thirty days after plants were inoculated with SCN, macronutrient concentrations of shoot and root tissues were determined. Potassium concentration in leaf blades was not affected; but K concentrations in leaf-petiole and stem tissues were increased with SCN infection. Roots infected with SCN contained lower K concentrations than uninfected roots, but only for the 2.4 mM K treatment. Thus, at the medium level of K fertility, SCN reduced K concentration in soybean roots, and increasing K fertility to the high level overcame the effect. Because K concentrations in the shoot tissues were not reduced by SCN infection, above ground portions of the plant may be able to overcome limitations that occur in roots during the first 30 days of infection. Increasing K fertility level in soybean fields may not benefit vegetative growth of soybean infected with SCN.     

Influences of high acidity and aluminum on the growth of lowland rice

Summary Lowland rice was grown on nutrient solutions in a continuous-flow system, with pH levels varying from 3.5 to 6.0. The chemical compositions of all nutrient solutions were alike, except for small amounts of HCl or KOH, needed for pH adjustments, and for variations in the Al supply.Rice was found not to be affected in its vegetative growth by H-ion concentrations up to that found at pH 3.5. High acidity suppressed the uptake of metallic cations without affecting vegetative growth.In low concentrations (0.05 and 0.2 ppm), Al suppressed the growth of rice seedlings. Concentrations ten times higher (0.5 and 2 ppm) appeared to be lethal to young rice plants. In contrast, 2 ppm Al when added to the nutrient solution past the seedling stage, exerted no adverse effect on the growth of rice. Two ppm Al, in chelated form, had no deleterious effect on rice in the seedling stage.The decreasing sensitivity of lowland rice to Al with advancing age of the plants might be of practical importance in regions where rice is grown on highly acid soils. By allowing the seedlings to develop on a seedbed consisting of soil close to neutrality, the plants may be transplanted into the acid soil once they have lost most of their initial sensitivity to high levels of soluble Al.     

Effect of withdrawal of phosphorus on nitrate assimilation and PEP carboxylase activity in tomato

Tomato plants (Lycopersicon esculentum) grown in a complete nutrient solution for 8 days were transferred to a P-free solution of pH 6.0. Within 2 days of transfer the rate of alkalinization of the nutrient solution declined and by 4 days the solution had become acid. Nitrate transferred from roots to leaves was depressed over this period, and the rate of nitrate reductase activity in the leaves (the main site of assimilation of nitrate in tomato) had declined by 60% within 5 days of transfer. The activity of PEP carboxylase in the leaves of the P-deficient plants increased after 3 days, eventually becoming 3 times greater than in the leaves of plants adequately supplied with P. The PEP carboxylase activity in the roots of the P-deficient plants increased within 2 days, becoming 4 times greater after 8 days' growth. These results are discussed in relation to mechanisms for enhancement of P acquisition and maintenance of cation and anion uptake during P-deficiency.     

Mechanism of phosphorus-induced zinc deficiency in cotton. II. Evidence for impaired shoot control of phosphorus uptake and translocation under zinc deficiency

Cotton (Gossypium hirsutum L. cv. Deltapine 15/21) plants were precultured for 19 to 25 days under controlled climatic conditions in nutrient solutions with different levels of Zn. With the onset of visual Zn-deficiency symptoms the pH of the nutrient solution decreased from 6.0 to about 5.0. In contrast, Zn-sufficient plants raised the pH of the nutrient solution to about 7.0. In short-term studies it could be demonstrated that the Zn nutritional status of the plants remarkably influenced the uptake and translocation rates of mineral nutrients. Compared to Zn-sufficient plants, P uptake rate in severely Zn-deficient plants was increased by a factor of 2 to 3, whereas the uptake rates of K, Ca and particularly NO₃ decreased. The accumulation of P in the roots of Zn-deficient plants was either not affected or even lower than in Zn-sufficient plants. Thus, Zn deficiency had a specific enhancement effect on root to shoot transport of P. This enhancement effect of Zn deficiency on uptake and transport of P was similar at nutrient solution pH values of 7.0 and 5.8; i.e. it was not the result of acidification of the nutrient solution. After application of ³⁶CI, ⁸⁶Rb and ³²P to plant stems, basipetal transport of ³⁶CI and ⁸⁶Rb was not affected by the Zn nutritional status of the plants. However, in Zn-deficient plants, only 7.8% of the ³²P was translocated basipetally compared to 34% in the Zn-sufficient plants. A resupply of Zn for 19 h to Zn-deficient plants enhanced basipetal ³²P transport. The results indicate that a feedback mechanism in the shoots is impaired in Zn-deficient plants which controls the P uptake by roots and especially the P transport from roots to shoots. As a result of this impairment toxic concentrations of P accumulate in the leaves. The mechanism responsible is likely the retranslocation of P in the phloem from shoots to roots.     

Nutrient interactions between phytoplankton and bacterioplankton under different carbon dioxide regimes

Light, nutrients, temperature, pH, and salinity are important factors in controlling the growth of phytoplankton and bacterioplankton. Supply of key nutrients to these communities can result in mutualistic or competitive relationships between bacterioplankton and phytoplankton. In this study, we investigated growth and uptake of nutrients by the marine prasinophyte flagellate Tetraselmis chui (strain PLY429) in the presence and absence of a community of bacterioplankton at two pH levels. Growth of PLY429 and total nutrient uptake were calculated for each treatment. The addition of bacterioplankton resulted in lower growth rates of PLY429, but the removal of ammonium was greater in those cultures with bacterioplankton present. The division rate of PLY429 was affected by pH; however, pH changes did not result in different uptake rates of nitrate, ammonium, or phosphate by the mixed algal and bacterial assemblage. These findings suggest that bacterioplankton and phytoplankton were competing for ammonium and that a lower pH resulted in more rapid algal growth. Mention of a trade name does not imply endorsement by the National Marine Fisheries Service.     

Kinetic properties of a phosphate-bond-driven glutamate-glutamine transport system in Streptococcus lactis and Streptococcus cremoris.

In Streptococcus lactis ML3 and Streptococcus cremoris Wg2 the uptake of glutamate and glutamine is mediated by the same transport system, which has a 30-fold higher affinity for glutamine than for glutamate at pH 6.0. The apparent affinity constant for transport (KT) of glutamine is 2.5 +/- 0.3 microM, independent of the extracellular pH. The KTS for glutamate uptake are 3.5, 11.2, 77, and 1200 microM at pH 4.0, 5.1, 6.0, and 7.0, respectively. Recalculation of the affinity constants based on the concentration of glutamic acid in the solution yield KTS of 1.8 +/- 0.5 microM independent of the external pH, indicating that the protonated form of glutamate, i.e., glutamic acid, and glutamine are the transported species. The maximal rates of glutamate and glutamine uptake are independent of the extracellular pH as long as the intracellular pH is kept constant, despite large differences in the magnitude and composition of the components of the proton motive force. Uptake of glutamate and glutamine requires the synthesis of ATP either from glycolysis or from arginine metabolism and appears to be essentially unidirectional. Cells are able to maintain glutamate concentration gradients exceeding 4 X 10(3) for several hours even in the absence of metabolic energy. The t1/2s of glutamate efflux are 2, 12, and greater than 30 h at pH 5.0, 6.0, and 7.0, respectively. After the addition of lactose as energy source, the rate of glutamine uptake and the level of ATP are both very sensitive to arsenate. When the intracellular pH is kept constant, both parameters decrease approximately in parallel (between 0.2 and 1.0 mM ATP) with increasing concentrations of the inhibitor. These results suggest that the accumulation of glutamate and glutamine is energized by ATP or an equivalent energy-rich phosphorylated intermediate and not by the the proton motive force.