Nitrate Storage Research Articles

Widespread occurrence of nitrate storage and denitrification among Foraminifera andGromiida

Benthic foraminifers inhabit a wide range of aquatic environments including open marine, brackish, and freshwater environments. Here we show that several different and diverse foraminiferal groups (miliolids, rotaliids, textulariids) and Gromia, another taxon also belonging to Rhizaria, accumulate and respire nitrates through denitrification. The widespread occurrence among distantly related organisms suggests an ancient origin of the trait. The diverse metabolic capacity of these organisms, which enables them to respire with oxygen and nitrate and to sustain respiratory activity even when electron acceptors are absent from the environment, may be one of the reasons for their successful colonization of diverse marine sediment environments. The contribution of eukaryotes to the removal of fixed nitrogen by respiration may equal the importance of bacterial denitrification in ocean sediments.

Nitrate responses of Arabidopsis cho1 mutants

We reported a loss-of-function of an Arabidopsis double AP2 transcription factor CHOTTO1 (CHO1) gene results in the altered responses to high concentrations of nitrate (~50 mM). Nitrate up to 10 mM promotes growth of the wildtype seedling, but inhibits it under higher concentrations. The cho1 seedlings responded to nitrate up to 10 mM similarly to the wildtype, but the inhibitory effect of excess nitrate is less prominent in the mutants. This phenotype is restricted to the cotyledons, and growth of the hypocotyl and roots of the cho1 mutants is inhibited by excess nitrate. The cho1 mutations caused the up-regulation of two nitrate transporter genes, AtNRT1.4 and At1g52190. Altered nitrate distribution and storage may explain the phenotypes of the cho1 mutants.

The Arabidopsis nitrate transporter NRT1.7, expressed in phloem, is responsible for source-to-sink remobilization of nitrate.

Several quantitative trait locus analyses have suggested that grain yield and nitrogen use efficiency are well correlated with nitrate storage capacity and efficient remobilization. This study of the Arabidopsis thaliana nitrate transporter NRT1.7 provides new insights into nitrate remobilization. Immunoblots, quantitative RT-PCR, beta-glucuronidase reporter analysis, and immunolocalization indicated that NRT1.7 is expressed in the phloem of the leaf minor vein and that its expression levels increase coincidentally with the source strength of the leaf. In nrt1.7 mutants, more nitrate was present in the older leaves, less (15)NO(3)(-) spotted on old leaves was remobilized into N-demanding tissues, and less nitrate was detected in the phloem exudates of old leaves. These data indicate that NRT1.7 is responsible for phloem loading of nitrate in the source leaf to allow nitrate transport out of older leaves and into younger leaves. Interestingly, nrt1.7 mutants showed growth retardation when external nitrogen was depleted. We conclude that (1) nitrate itself, in addition to organic forms of nitrogen, is remobilized, (2) nitrate remobilization is important to sustain vigorous growth during nitrogen deficiency, and (3) source-to-sink remobilization of nitrate is mediated by phloem.

ATP Binding to the C Terminus of the Arabidopsis thaliana Nitrate/Proton Antiporter, AtCLCa, Regulates Nitrate Transport into Plant Vacuoles

Nitrate, one of the major nitrogen sources for plants, is stored in the vacuole. Nitrate accumulation within the vacuole is primarily mediated by the NO(3)(-)/H(+) exchanger AtCLCa, which belongs to the chloride channel (CLC) family. Crystallography analysis of hCLC5 suggested that the C-terminal domain, composed by two cystathionine beta-synthetase motifs in all eukaryotic members of the CLC family is able to interact with ATP. However, interaction of nucleotides with a functional CLC protein has not been unambiguously demonstrated. Here we show that ATP reversibly inhibits AtCLCa by interacting with the C-terminal domain. Applying the patch clamp technique to isolated Arabidopsis thaliana vacuoles, we demonstrate that ATP reduces AtCLCa activity with a maximum inhibition of 60%. ATP inhibition of nitrate influx into the vacuole at cytosolic physiological nitrate concentrations suggests that ATP modulation is physiologically relevant. ADP and AMP do not decrease the AtCLCa transport activity; nonetheless, AMP (but not ADP) competes with ATP, preventing inhibition. A molecular model of the C terminus of AtCLCa was built by homology to hCLC5 C terminus. The model predicted the effects of mutations of the ATP binding site on the interaction energy between ATP and AtCLCa that were further confirmed by functional expression of site-directed mutated AtCLCa.

Physiological responses of intertidal marine brown algae to nitrogen deprivation and resupply of nitrate and ammonium.

Intertidal macroalgae Fucus and Laminaria experience seasonally fluctuating inorganic N supply. This study examined the effects of long-term N deprivation, recovery following N resupply, and effects of elevated ammonium and nitrate exposure on N acquisition in intertidal algae using manipulations of N supply in tank culture. Over 15 weeks of N deprivation, internal N and nitrate reductase activity (NRA) declined, but maximum quantum yield of PSII was unaffected in Fucus serratus and Fucus vesiculosus. Low NRA was maintained despite no external nitrate availability and depletion of internal pools, suggesting a constitutive NRA, insensitive to N supply. Nitrate resupplied to N-starved thalli was rapidly taken up and internal nitrate pools and NRA increased. Exposure to elevated (50 microM) nitrate over 4 days stimulated nitrate uptake and NRA in Laminaria digitata and F. serratus. Exposure to elevated ammonium suppressed NRA in L. digitata but not in F. serratus. This novel insensitivity of NRA to ammonium in Fucus contrasts with regulation of NRA in other algae and higher plants. Ammonium suppression of NRA in L. digitata was not via inhibition of nitrate uptake and was independent of nitrate availability. L. digitata showed a higher capacity for internal nitrate storage when exposed to elevated ambient nitrate, but NRA was lower than in Fucus. All species maintained nitrate assimilation capacity in excess of nitrate uptake capacity. N uptake and storage strategies of these intertidal macroalgae are adaptive to life in fluctuating N supply, and distinct regulation of N metabolism in Fucus vs Laminaria may relate to position in the intertidal zone.

Effect of supports on formation and reduction rate of stored nitrates on NSR catalysts as investigated by in situ FT/IR

Surface dynamics of nitrates on NOx storage–reduction (NSR) catalysts are examined by means of in situ FT/IR. In the initial state of NOx storage, both nitrite and nitrates are formed on Pt–Ba/Al 2O 3 surface, and then nitrite become abundant with the increase of storage time. The initial rate of nitrate storage is faster in a flow of NO/O 2 mixture than in a flow of NO 2 without O 2. The presence of oxygen is found to be essential for the conversion of surface nitrite to nitrates. The rate and amount of nitrate formation are strongly affected by type of supports. The storage ability is in the order of MgO > Al 2O 3 > ZrO 2 > SiO 2, which is in accordance with that of basicity of the supports. On the other hand, the rate of nitrate reduction by H 2 is in the different order: Al 2O 3 > ZrO 2 > SiO 2 > MgO. The strong contribution of acid–base property of supports as a controlling factor is suggested.

Plant response to nitrate starvation is determined by N storage capacity matched by nitrate uptake capacity in two Arabidopsis genotypes

In a low-input agricultural context, plants facing temporal nutrient deficiencies need to be efficient. By comparing the effects of NO(3)(-)-starvation in two lines of Arabidopsis thaliana (RIL282 and 432 from the Bay-0xShahdara population), this study aimed to screen the physiological mechanisms allowing one genotype to withstand NO(3)(-)-deprivation better than another and to rate the relative importance of processes such as nitrate uptake, storage, and recycling. These two lines, chosen because of their contrasted shoot N contents for identical shoot biomass under N-replete conditions, underwent a 10 d nitrate starvation after 28 d of culture at 5 mM NO(3)(-). It was demonstrated that line 432 coped better with NO(3)(-)-starvation, producing higher shoot and root biomass and sustaining maximal growth for a longer time. However, both lines exhibited similar features under NO(3)(-)-starvation conditions. In particular, the nitrate pool underwent the same drastic and early depletion, whereas the protein pool was increased to a similar extent. Nitrate remobilization rate was identical too. It was proportional to nitrate content in both shoots and roots, but it was higher in roots. One difference emerged: line 432 had a higher nitrate content at the beginning of the starvation phase. This suggests that to overcome NO(3)(-)-starvation, line 432 did not directly rely on the N pool composition, nor on nitrate remobilization efficiency, but on higher nitrate storage capacities prior to NO(3)(-)-starvation. Moreover, the higher resistance of 432 corresponded to a higher nitrate uptake capacity and a 2-9-fold higher expression of AtNRT1.1, AtNRT2.1, and AtNRT2.4 genes, suggesting that the corresponding nitrate transporters may be preferentially involved under fluctuating N supply conditions.

Physiological Adaptation of a Nitrate-Storing Beggiatoa sp. to Diel Cycling in a Phototrophic Hypersaline Mat

The aim of this study was to investigate the supposed vertical diel migration and the accompanying physiology of Beggiatoa bacteria from hypersaline microbial mats. We combined microsensor, stable-isotope, and molecular techniques to clarify the phylogeny and physiology of the most dominant species inhabiting mats of the natural hypersaline Lake Chiprana, Spain. The most dominant morphotype had a filament diameter of 6 to 8 microm and a length varying from 1 to >10 mm. Phylogenetic analysis by 16S rRNA gene comparison revealed that this type appeared to be most closely related (91% sequence identity) to the narrow (4-microm diameter) nonvacuolated marine strain MS-81-6. Stable-isotope analysis showed that the Lake Chiprana species could store nitrate intracellularly to 40 mM. The presence of large intracellular vacuoles was confirmed by fluorescein isothiocyanate staining and subsequent confocal microscopy. In illuminated mats, their highest abundance was found at a depth of 8 mm, where oxygen and sulfide co-occurred. However, in the dark, the highest Beggiatoa densities occurred at 7 mm, and the whole population was present in the anoxic zone of the mat. Our findings suggest that hypersaline Beggiatoa bacteria oxidize sulfide with oxygen under light conditions and with internally stored nitrate under dark conditions. It was concluded that nitrate storage by Beggiatoa is an optimal strategy to both occupy the suboxic zones in sulfidic sediments and survive the dark periods in phototrophic mats.

Biological and chemical sulfide oxidation in a Beggiatoa inhabited marine sediment

The ecological niche of nitrate-storing Beggiatoa, and their contribution to the removal of sulfide were investigated in coastal sediment. With microsensors a clear suboxic zone of 2-10 cm thick was identified, where neither oxygen nor free sulfide was detectable. In this zone most of the Beggiatoa were found, where they oxidize sulfide with internally stored nitrate. The sulfide input into the suboxic zone was dominated by an upward sulfide flux from deeper sediment, whereas the local production in the suboxic zone was much smaller. Despite their abundance, the calculated sulfide-oxidizing capacity of the Beggiatoa could account for only a small fraction of the total sulfide removal in the sediment. Consequently, most of the sulfide flux into the suboxic layer must have been removed by chemical processes, mainly by precipitation with Fe2+ and oxidation by Fe(III), which was coupled with a pH increase. The free Fe2+ diffusing upwards was oxidized by Mn(IV), resulting in a strong pH decrease. The nitrate storage capacity allows Beggiatoa to migrate randomly up and down in anoxic sediments with an accumulated gliding distance of 4 m before running out of nitrate. We propose that the steep sulfide gradient and corresponding high sulfide flux, a typical characteristic of Beggiatoa habitats, is not needed for their metabolic performance, but rather used as a chemotactic cue by the highly motile filaments to avoid getting lost at depth in the sediment. Indeed sulfide is a repellent for Beggiatoa.

Nitrate transporters and peptide transporters

In higher plants, two types of nitrate transporters, NRT1 and NRT2, have been identified. In Arabidopsis, there are 53 NRT1 genes and 7 NRT2 genes. NRT2 are high-affinity nitrate transporters, while most members of the NRT1 family are low-affinity nitrate transporters. The exception is CHL1 (AtNRT1.1), which is a dual-affinity nitrate transporter, its mode of action being switched by phosphorylation and dephosphorylation of threonine 101. Two of the NRT1 genes, CHL1 and AtNRT1.2, and two of the NRT2 genes, AtNRT2.1 and AtNRT2.2, are known to be involved in nitrate uptake. In addition, AtNRT1.4 is required for petiole nitrate storage. On the other hand, some members of the NRT1 family are dipeptide transporters, called PTRs, which transport a broad spectrum of di/tripeptides. In barley, HvPTR1, expressed in the plasma membrane of scutellar epithelial cells, is involved in mobilizing peptides, produced by hydrolysis of endosperm storage protein, to the developing embryo. In higher plants, there is another family of peptide transporters, called oligopeptide transporters (OPTs), which transport tetra/pentapeptides. In addition, some OPTs transport GSH, GSSH, GSH conjugates, phytochelatins, and metals.

Pt and Nb species on various supports: An alternative to current materials for NO x removal

Meso- or micro/mesoporous supports (NbMCM-41 and NaY + NbMCM-41, respectively) were tested for Pt loading. The effects of the support structure and composition on the metal oxidation and on nitrate storage properties were pointed out in the SCR for NO x removal. Nitrate species were found directly related to the catalytic performance of Pt. Niobium from NbMCM-41 matrix in Pt/NbMCM-41 play the role of NO x storage species, whereas in the presence of NaY in the support, sodium cations act as storage for NO x .

MnOx-CeO2 mixed oxides for the low-temperature oxidation of diesel soot

TG-FTIR and flow reactor experiments were performed to study soot oxidation on MnOx-CeO2 mixed oxide catalysts in model diesel exhaust gas (10% O2, 5% H2O, 1000ppm NO, balance N2). The ignition temperature in TG-FTIR experiments for a 1:20 mixture of soot and catalyst was found to be ∼280°C, which is significantly lower than for the individual oxides.It was found that NO is oxidized over the catalyst to NO2, which is stored on the catalyst as nitrate at low temperatures. At higher temperatures the nitrates decompose, releasing NO2 to the gas phase which acts as the oxidizing agent for soot. The nitrate storage capacity of MnOx-CeO2 is three to five times higher than that of the individual oxides resulting in a major contribution of the released NO2 to the soot oxidation process. This explains the strong synergistic effect of manganese and cerium in the mixed oxide on the soot oxidation.Adding SO2 to the model gas resulted in a deactivation of the catalyst, which is traced to the loss of the NO oxidation activity. The sulphates could be decomposed by heating the catalyst under reducing as well as oxidizing conditions. However, the initial activity of the catalyst could not be restored.

Nutrient and iron limitation to Ulva blooms in a eutrophic coastal lagoon (Sacca di Goro, Italy)

Growth patterns and bloom formation of the green seaweed Ulva rigida were analysed in the eutrophic Sacca di Goro lagoon (Po River Delta, Italy). Variations of standing biomasses and elemental composition of Ulva were analysed through an annual cycle with respect to nitrogen, phosphorus and iron. Growth rates, nutrient and iron uptake and nitrate storage by macroalgal thalli were also assessed with field experiments during the formation of a spring bloom. The control of Ulva growth and the bloom formation depended on multiple factors, especially on nitrogen availability and iron deficiency. In the nitrate rich waters of the Sacca di Goro lagoon, nitrate accumulation in Ulva thalli was inversely related with Fe uptake, indicating an influence of Fe limitation on N acquisition. Since length and magnitude of nitrate luxury uptake are inversely related to the size of the intracellular nitrate pools, in nitrate rich waters the fast growing Ulva may face risk of N-limitation not only when exposed to low N concentrations or at high biomass levels, but also when exposed to pulsed dissolved nitrate concentrations at low iron availability. The potential Fe limitation could be affected by processes controlled by geochemical reactions and by macroalgal growth and decomposition. Both Fe oxidation during the active macroalgal growth and the formation of insoluble FeS and FeS2 during bloom collapse can result in a drastic decrease of soluble iron. Thus, a potential limitation of Fe to macroalgae can occur, determining positive feedbacks and potentially controlling the extent of bloom development and persistence.

Light-Dark Changes in Cytosolic Nitrate Pools Depend on Nitrate Reductase Activity in Arabidopsis Leaf Cells

Several different cellular processes determine the size of the metabolically available nitrate pool in the cytoplasm. These processes include not only ion fluxes across the plasma membrane and tonoplast but also assimilation by the activity of nitrate reductase (NR). In roots, the maintenance of cytosolic nitrate activity during periods of nitrate starvation and resupply (M. van der Leij, S.J. Smith, A.J. Miller [1998] Planta 205: 64-72; R.-G. Zhen, H.-W. Koyro, R.A. Leigh, A.D. Tomos, A.J. Miller [1991] Planta 185: 356-361) suggests that this pool is regulated. Under nitrate-replete conditions vacuolar nitrate is a membrane-bound store that can release nitrate to the cytoplasm; after depletion of cytosolic nitrate, tonoplast transporters would serve to restore this pool. To study the role of assimilation, specifically the activity of NR in regulating the size of the cytosolic nitrate pool, we have compared wild-type and mutant plants. In leaf mesophyll cells, light-to-dark transitions increase cytosolic nitrate activity (1.5-2.8 mm), and these changes were reversed by dark-to-light transitions. Such changes were not observed in nia1nia2 NR-deficient plants indicating that this change in cytosolic nitrate activity was dependent on the presence of functional NR. Furthermore, in the dark, the steady-state cytosolic nitrate activities were not statistically different between the two types of plant, indicating that NR has little role in determining resting levels of nitrate. Epidermal cells of both wild type and NR mutants had cytosolic nitrate activities that were not significantly different from mesophyll cells in the dark and were unaltered by dark-to-light transitions. We propose that the NR-dependent changes in cytosolic nitrate provide a cellular mechanism for the diurnal changes in vacuolar nitrate storage, and the results are discussed in terms of the possible signaling role of cytosolic nitrate.

P-immobilisation and phosphatase activities in lake sediment following treatment with nitrate and iron

The influence of a further developed inlake restoration method on the P-immobilisation and microbial activities, especially under anoxic conditions was investigated. The impact of nitrate and iron dosing with a newly developed nitrate storage compound (Depox ®Fe) was tested in enclosures in the eutrophic dimictic Lake Dagowsee, Germany. Additions of 50 g m −2 of NO 3 −–N and 66 g m −2 of Fe 3+ ensured availability of nitrate at the sediment surface during a 2-months period. As a result the phosphate release from the anoxic sediments was completely suppressed even 1 year after the application. The hypolimnetic deoxygenation was unaffected by the Depox ®Fe addition. However, sulfur reduction and methanogenesis were inhibited and the phosphatase activity increased.

Response of Enteromorpha sp. (Chlorophyceae) to a nitrate pulse: nitrate uptake, inorganic nitrogen storage and nitrate reductase activity

The uptake, storage and reduction of nitrate (NO3 - ) by Enteromorpha sp. during a NO3 - pulse was studied in the laboratory using algae collected from the Mobile Bay estuary, Alabama, USA. Peak uptake occurred when Enteromorpha sp. was initially exposed to NO3 - . As the internal NO3 - pool filled, NO3 - uptake declined. After 6 h of exposure to a 30 µM NO3 - pulse, the tissue NO3 - pool was filled and NO3 - uptake decreased to 1.64 ± 2.63 µmol NO3 - g -1 fresh wt h -1 . While tissue NO3 - increased when NO3 - became available, the size of the internal nitrite (NO2 - ), ammonium (NH4 + ), and free amino acid (FAA) pools remained roughly constant, suggesting that reduction of NO3 - to nitrite (NO2 - ) by nitrate reductase (NR) was the rate-limiting step in NO3 - assimilation. Meanwhile, there was a lag time (2 to 3 h) between exposure to NO3 - and peak NR activity (0.80 ± 0.23 µmol NO2 - g -1 fresh wt h -1 ). These characteristics, combined with a peak NR activity that was 11-fold less than the peak NO3 - uptake rate, suggest that during a NO3 - pulse the internal NO3 - pool quickly fills and uptake becomes limited by the rate at which the internal NO3 - pool is reduced by NR. Predicted levels of tissue NO3 - calculated from initial tissue NO3 - , NO3 - uptake and NR activity agreed with the measured tissue NO3 - .

Quantified NOx adsorption on Pt/K/gamma-Al2O3 and the effects of CO2 and H2O

A multi-component NOx-trap catalyst consisting of Pt and K supported on γ-Al2O3 was studied at 250°C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H2O and CO2 on NOx storage. The Al2O3 support was shown to have NOx trapping capability with and without Pt present (at 250°C Pt/Al2O3 adsorbs 2.3μmols NOx/m2). NOx is primarily trapped on Al2O3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2μmols NOx/m2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al2O3 catalyst are coordinated on the Al2O3 support at saturation.When 5% CO2 was included in a feed stream with 300ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition.

Quantitative trait loci analysis of nitrate storage in Arabidopsis leading to an investigation of the contribution of the anion channel gene, AtCLC-c, to variation in nitrate levels.

Storage of excess nitrate in the vacuole and its subsequent remobilization is an important aspect of a plant's nitrogen economy, but the genes controlling the underlying processes have not all been identified and characterized. Cape Verdi Island (Cvi)/Landsberg erecta (Ler) and Columbia (Col)/Landsberg erecta recombinant inbred line (RIL) populations of Arabidopsis thaliana were used to identify quantitative trait loci (QTL) controlling natural variation in nitrate concentrations. One major and two minor QTLs were found for the Cvi/Ler population and one minor QTL for the Col/Ler RIL. These were designated NA1 to NA4. The major Cvi/Ler QTL (NA3) was located at the bottom of chromosome 5. No interaction among the QTLs was found by two-way ANOVA. By comparing in silico the locations of the QTLs with a physical map of the Arabidopsis genome, candidate genes for each QTL were identified. Several of these were anion channels of the AtCLC family. One of these, AtCLC-c, coincided with NA3 and its role was investigated using a mutant with a transposon insertion in AtCLC-c. Mutant plants homozygous for the insertion (designated clcc-1) had less than 5% of AtCLC-c mRNA compared with wild-type (WT) shoots. They also had significantly lower nitrate concentrations when grown at a range of external nitrate concentrations. The concentrations of chloride, malate, and citrate were also affected in the mutant. In wild-type plants, expression of AtCLC-c was down-regulated in the presence of nitrate, but ammonium had a much smaller effect while chloride and sulphate did not affect expression. These and published results suggest that multiple genes affect nitrate concentrations in plants and that AtCLC-c and other members of the AtCLC gene family play some role in this.

In vitro effect of nanoleakage expression on resin-dentin bond strengths analyzed by microtensile bond test, SEM/EDX and TEM

This study evaluated the effect of multiple consecutive adhesive resin coatings of adhesive bonded to human dentin on nanoleakage and resin–dentin bond strength. Resin bonded dentin specimens were prepared using a total-etch adhesive (One-Step Plus) applied as multiple consecutive coating, or using two self-etch adhesive systems (iBond or Fluoro Bond). For the total-etch adhesive, resin application and air evaporation were performed 1, 2, 3, or 4 times. The self-etch adhesives were applied according to manufacturers’ instructions. Resin–dentin bonded beams were prepared and immersed in water (control) or ammoniacal silver nitrate. After storage, microtensile bond strengths were measured. The fractured surfaces were examined by scanning and transmission electron microscopy (SEM and TEM), and energy-dispersive X-ray spectrometry (EDX). No significant differences in bond strength were found between water and silver nitrate storage groups. Several types of silver depositions (spotted, reticular, or water trees) were found in adhesive joints. The bond strengths of the single coated specimens of the total-etch adhesive were significantly lower than those receiving 2–4 coatings. Single coats produced more nanoleakage than multiple coats. However, no correlation was found between the bond strengths and nanoleakage between the different adhesives (total-etch adhesive with different conditions or self-etch adhesives).

Nutrient translocation in the xylem of poplar--diurnal variations and spatial distribution along the shoot axis.

This investigation shows diurnal variations in the xylem sap composition of poplar (Populus tremula x P. alba). All major macronutrients reached a maximum concentration in the first half of the light period and decreased to the middle of the night. The relative abundance of the nutrients did not change during the day. The sap flow, which responded very fast to the environmental changes (2.2-fold increase within 10-20 min of illumination), reached a maximum value in the second half of the light period. Transpiration (and photosynthesis) was constant throughout the light phase. The calculated translocation rates displayed a maximum in the first half of the light period and therefore did not fit the time course of sap flow. During the night, translocation rates were 63-69% lower than the maximum. The regulation of nutrient translocation is discussed taking the active xylem loading into account. The axial distribution located the nitrate assimilation in younger leaves and storage of nitrate (and other macronutrients) in older leaves. Nitrate and potassium concentrations in the xylem sap did not change along the plant axis. However, the sap flow was greater in younger shoot sections than in older sections. We assume that the greater demand for nitrate in the younger shoot section was satisfied via an increased volume flow rather an increased nitrate concentration.