Differences In Uptake Rates Research Articles

Plant uptake of dual-labeled organic N biased by inorganic C uptake: Results of a triple labeling study

Direct plant uptake of organic nitrogen (N) is often studied using the dual-labeling approach ( 15N + 13C or 15N + 14C). However, the method might be hampered by uptake of labeled inorganic carbon (C) produced by mineralization of labeled organic compounds. Here we report the results from a triple labeling experiment ( 15N + 13C + 14C) investigating whether root uptake of labeled inorganic C can bias the results obtained in studies of organic N uptake using dual-labeled amino acids ( 15N, 13C). In a rhizosphere tube experiment we investigated 13C and 14C uptake by maize either supplied with labeled glycine or CO 3 2 − , but found no differences in uptake rates between these C-sources. The uptake of inorganic C to the shoot tissue was higher for maize grown in full light compared to shading, which indicates a passive uptake of inorganic C with water. We conclude that uptake of inorganic C produced by mineralization of amino acids can significantly bias the interpretations of organic N uptake studies using dual-labeling.

Field calibration of polyurethane foam disk passive air samplers for PBDEs

A field study was performed to derive uptake rates of airborne polybrominated diphenyl ethers (PBDEs) to polyurethane foam (PUF) disk passive air samplers (PAS) and to investigate the influence of deployment location and device design. Data are presented on the gas-particle partitioning of PBDEs, since atmospheric phase distribution was considered to be a variable which could affect sampler performance. Uptake rates for these compounds were similar to those derived previously for other classes of persistent organic pollutants (POPs) (approximately 2-6 m(3)/day), with rates higher for the higher brominated species. Whilst other compound classes (e.g. polychlorinated biphenyls) are predominantly present in the air in the gas phase, heavier PBDEs have an association with particulates in the atmosphere at ambient temperatures. In this study, the PUF disk PAS therefore sampled PBDEs present in the gas phase and on fine aerosols with a similar sampling efficiency to those which are predominantly gas phase compounds. Compounds which are exclusively on particles are sampled less efficiently. A comparison of the three most commonly used PUF deployment configurations, used by different research groups, indicated little difference in uptake rates. The ranges of derived air concentrations for BDE-47, -99, and -183 between three sampler designs were 7.5-9.8, 7.4-12.4, and 4.7-6.6 pg/m(3), respectively. This suggests the robustness of this sampler in comparisons between regional and global campaigns where these three designs are employed.

Field Deployment of Polyethylene Devices to Measure PCB Concentrations in Pore Water of Contaminated Sediment

Sediment pore water concentrations of polychlorinated biphenyls (PCBs) in a contaminated mudflat in San Francisco Bay, CA were determined by field-deployed polyethylene devices (PEDs). Sequential sampling of PEDs deployed in the field showed large differences in uptake rates and time to equilibrium compared to PEDs mixed with field-collected sediment in the laboratory. We demonstrate a modeling approach that involves the use of impregnated performance reference compounds (PRCs) and interpretation of the data either by PCB molar volume adjustment or environmental adjustment factors to measure pore water concentrations of 118 PCB congeners. Both adjustment methods predicted comparable sampling rates, and PCB pore water concentrations estimated by use of the molar volume adjustment method were similar to values analytically measured in pore waters from the laboratory and field. The utility of PEDs for sampling pore water in the field was evaluated at a tidal mudflat amended with activated carbon to sequester PCBs. Pore water concentrations decreased up to 60% within 18 months after activated carbon amendment, as compared to a mechanical-mixed control plot Results of this study illustrate PEDs provide an inexpensive, in situ method to measure total PCB contamination in sediment pore water using a small set of PRCs.

Populations who die without specialist palliative care: does lower uptake equate with unmet need?

Background: In palliative care, the target population (all people with life-limiting illnesses and their family/caregivers) and the complexity of their needs from diagnosis to bereavement should define the subpopulation who access specialist palliative care services (SPCS). Have caregivers of patients who have not accessed SPCS had their needs met? Methods: As part of a broader state-wide randomized face-to-face population health survey over six years (18 224 interviews, 71% response), questions were asked of people bereaved in the previous five years when someone close to them died an `expected' death (39% of respondents). Questions included respondent demographics, the diagnosis of the deceased and, for one year, whether SPCS was of benefit (if used) or needed (if not used). Differential uptake rates were calculated for diagnosis, income, country of birth and age and 2 × 2 tables reflecting the accuracy of match of service with caregiver needs were generated for each group (accuracy = true positives + true negatives/total) *100. Results: Uptake of SPCS was significantly lower in people with a non-cancer diagnosis (40% versus 62%; P = 0.0001), lower income (56% versus 61%; P = 0.0006) and people born where English was not the first language (52% versus 58%; P = 0.0096). The only subgroup where the accuracy of matching between palliative care service uptake and identified needs was lower than the overall average (83%) was where cancer was not the life-limiting illness (69%; cancer 86%). Discussion: SPCS under utilization has previously been described in the population subgroups explored in this study and assumed to equal unmet needs and poorer outcomes. Caregiver responses suggest that, except for people with a non-cancer diagnosis, lack of service uptake may not represent unmet needs. These results are limited to people with caregivers. Palliative Medicine 2008; 22: 43—50

Kinetic analysis of 99mTc-sestamibi evaluates the protective effects by ischaemic preconditioning on ischaemic myocardium in an isolated rabbit heart

To analyse the kinetic changes of uptake, washout and retention of Tc-sestamibi in order to evaluate the protective effects and possible mechanism of ischaemic preconditioning and adenosine preconditioning on myocardium injured by ischaemia/reperfusion. Isolated ischaemia/reperfusion rabbit heart models, as established by Langendorff, were used. Eighteen rabbit hearts perfused in Krebs-Henseleit (KH) buffer were randomly assigned to three groups: ischaemia/reperfusion (I/R, n=6), adenosine preconditioning (AD, n=6), and ischaemic preconditioning (IPC, n=6). Tc-sestamibi (55.5 MBq) in KH was perfused for 40 min and washed out for 40 min. The kinetic changes of Tc-sestamibi within myocardial tissue was monitored during the uptake and washout phases. Cardiac haemodynamic parameters, creatine kinase and lactate dehydrogenase leakage in coronary effluent, and myocardial infarct size were measured to assess myocardial injuries in rabbit hearts. In the early phases of uptake, there were no significantly different uptake rates of Tc-sestamibi between AD (before 20 min), IPC (before 15 min) and I/R myocardium (all P>0.05). Uptake rates of Tc-sestamibi in myocardium of the three groups all tended to increase, with the uptake time increasing. In the late phases of uptake, AD and IPC were significantly higher than I/R (all P<0.05). In the washout phases, the retention fractions of Tc-sestamibi in myocardium of the three groups all showed a descending tendency with washout time increasing. The retention fractions in AD and IPC were all higher than I/R (all P<0.05). There were no statistical differences in uptake rates and retention fractions of Tc-sestamibi between AD and IPC (all P>0.05). Cardiac haemodynamic parameters, creatine kinase and lactate dehydrogenase leakage, and myocardial infarct size demonstrated there is lighter injury in AD and IPC myocardium than in I/R (all P<0.05). The retention of Tc-sestamibi and myocardial infarction weight were significantly negatively correlated (r=-0.8384, P<0.001). Adenosine preconditioning has similar myocardial protective effects on ischaemia/reperfusion myocardium as does ischaemic preconditioning. Tc-sestamibi may be a sensitive and reliable measure for evaluating the importance and mechanism of ischaemic preconditioning and adenosine preconditioning.

Sensitivity of marine microalgae to copper: The effect of biotic factors on copper adsorption and toxicity

Microalgae are sensitive indicators of environmental change and, as the basis of most freshwater and marine ecosystems, are widely used in the assessment of risk and development of environmental regulations for metals. However, interspecies differences in sensitivity to metals are not well understood. The relationship between metal-algal cell binding and copper sensitivity of marine microalgae was investigated using a series of 72-h growth-rate inhibition bioassays and short-term (1-h) uptake studies. A range of marine algae from different taxonomic groups were screened to determine whether copper adsorption to the cell membrane was influenced by biotic factors, such as the ultrastructure of cell walls and cell size. Minutocellus polymorphus was the most sensitive species to copper and Dunaliella tertiolecta the least sensitive, with 72-h IC50 values (concentration to inhibit growth-rate by 50%) of 0.6 and 530 microg Cu/L, respectively. Copper solution-cell partition coefficients at equilibrium (K(d)) were calculated for six species of algae on a per cell and surface area basis. The largest and smallest cells had the lowest and highest K(d) values, respectively (on a surface area basis), with a general (non-linear) trend of decreasing K(d) with increasing cell surface area (p=0.026), however, no relationship was found between K(d) and copper sensitivity, nor cell size and copper sensitivity. Interspecies differences in copper sensitivity were not related to cell size, cell wall type, taxonomic group or K(d) values. The differences in sensitivity may be due to differences in uptake rates across the plasma membrane, in internal binding mechanisms and/or detoxification mechanisms between the different microalgal species.

Little effect of excessive biofouling on the uptake of organic contaminants by semipermeable membrane devices

The effects of water flow rate and antifouling agents on the extent of biofouling and on the uptake of non-polar organic contaminants by semipermeable membrane devices (SPMDs) were studied during four field experiments in the Western Wadden Sea. Biofouling densities on the sampler surface ranged from 0.3 to 16 g dry weight dm −2. Water sampling rates were estimated from the dissipation rates of performance reference compounds (PRCs). The antifouling agents Irgarol and capsaicin (33 mg per ml triolein) had no noticeable effect on the extent of fouling, and caused only a 5–10% increase in the absorbed amounts. Enhanced flow rates had only a minimal effect on the amount of biofouling, but caused the water sampling rates to increase by a factor of 1.2–2. Increases in PRC-derived sampling rates were reflected by increases in the absorbed amounts for compounds that were in the linear uptake stage of the sampling process. The results imply (1) that extreme biofouling does not always result in reduced sampling rates, (2) that extreme biofouling does not preclude the existence of flow effects on the sampling rates, and (3) that differences in uptake rates are quantitatively reflected by the dissipation rates of PRCs.

Uptake–toxicity relationships of a series of N-substituted N′-(4-imidazole-ethyl)thiourea in precision-cut rat liver slices

A previous study showed that the cytotoxicity of a series of N-p-phenyl-substituted N′-(4-imidazole-ethyl)thiourea in precision-cut rat liver slices increased with increasing electron-withdrawing capacity of the p-substituent and may be related to the Vmax/Km values of bioactivation of the thiourea-moiety by hepatic flavin-containing monooxygenases (FMOs). However, differences in the uptake of xenobiotics into precision-cut liver slices can also have consequences for the rates of metabolism of xenobiotics. In the present study, therefore, we investigated the rate and nature of uptake of 9 N-substituted N′-(4-imidazole-ethyl)thiourea into precision-cut rat liver slices. It was found that a five-fold difference exists among a series of N-substituted N′-(4-imidazole-ethyl)thiourea both in the initial rate of uptake and in the steady-state levels ultimately achieved in the precision-cut rat liver slices. It appeared that the most cytotoxic compounds were also the most readily absorbed compounds. The concentration-dependent initial rate of uptake could be described by a carrier-mediated saturable component and a non-saturable component. At cytotoxic concentrations, the non-saturable component accounted for more than 95% of the total uptake. From this study, it is concluded that differences in rate of uptake of thiourea-containing compounds may be a contributing factor to the differences in bioactivation by FMOs as the basis of the structure–toxicity relationships observed in precision-cut rat liver slices.

In situ measurement of water absorption by fine roots of three temperate trees: species differences and differential activity of superficial and deep roots.

The spatial heterogeneity of water uptake by fine roots under field conditions was analyzed in situ with miniature sap flow gauges in a mature beech-oak-spruce mixed stand. Sap flow rate (J), sap flow density (Jd), and root surface-area-specific flow rate (uptake rate, Js) were measured for eight to 10 small-diameter roots (3-4 mm) per species in the organic layer (superficial roots) and in the mineral soil (30-80 cm, deep roots) during four months in summer 1999. We calculated Js by relating J to the surface area of the section of the fine root system distal to the position of the gauge on the root. When measured synchronously, roots of the three species did not differ significantly in mean Js, although oak roots tended to have lower rates. However, Jd decreased in the sequence spruce > beech > oak in most measurement periods. Microscopic investigation revealed differences in fine root anatomy that may partly explain the species differences in Jd and Js. Oak fine roots had a thicker periderm than beech and spruce roots of similar diameter and spruce roots had fewer fine branch rootlets than the other species. Synchronously recorded Jd and Js of nearby roots of the same tree species showed large differences in flow with coefficients of variation from 25 to 150% that could not be explained by patchy distribution of soil water. We hypothesize that the main cause of the large spatial heterogeneity in root water uptake is associated with differences between individual roots in morphology and ultrastructure of the root cortex that affect root radial and root-soil interface conductivities. The high intraspecific variation in Js may mask species differences in root water uptake. Superficial roots of all species typically had about five times higher Jd than deep roots of the same species. However, Js values were similar for superficial and deep roots in beech and spruce because small diameter roots of both species were more branched in the organic layer than in mineral soil. In oak, deep roots had lower Js (maximum of 100 g m(-2) day(-1)) than superficial roots (about 1000 g m(-2) day(-1)). We conclude that temperate tree species in mixed stands have different water uptake capacities. Water flow in the rhizosphere of forests appears to be a highly heterogeneous process that is influenced by both tree species and differences in uptake rates of individual roots within a species.

Processes modulating calcium distribution in citrus leaves. An investigation using x-ray microanalysis with strontium as a tracer.

Citrus leaves accumulate large amounts of calcium that must be compartmented effectively to prevent stomatal closure by extracellular Ca2+ and interference with Ca(2+)-based cell signaling pathways. Using x-ray microanalysis, the distribution of calcium between vacuoles in different cell types of leaves of rough lemon (Citrus jambhiri Lush.) was investigated. Calcium was accumulated principally in palisade, spongy mesophyll, and crystal-containing idioblast cells. It was low in epidermal and bundle sheath cells. Potassium showed the reverse distribution. Rubidium and strontium were used as tracers to examine the pathways by which potassium and calcium reached these cells. Comparisons of strontium and calcium distribution indicated that strontium is a good tracer for calcium, but rubidium did not mirror the potassium distribution pattern. The amount of strontium accumulated was highest in palisade cells, lowest in bundle sheath and epidermal cells, and intermediate in the spongy mesophyll. Accumulation of strontium in palisade and spongy mesophyll was accompanied by loss of potassium from these cells and its accumulation in the bundle sheath. Strontium moved apoplastically from the xylem to all cell types, and manipulation of water loss from the adaxial leaf surface suggested that diffusion is responsible for strontium movement to this side of the leaf. The results highlight the importance of palisade and spongy mesophyll as repositories for calcium and suggest that calcium distribution between different cell types is the result of differential rates of uptake. This tracer technique can provide important information about the ion uptake and accumulation properties of cells in intact leaves.

The effects of temperature and nutrient concentrations on nitrate and phosphate uptake in different species of Porphyra from Long Island Sound (USA)

Uptake rates of nitrate and phosphate were measured for four species and one variety of Porphyra from Long Island Sound (USA) at two temperatures and two nutrient medium concentrations at increasing intervals over a 24- or 48-h period. Maximum uptake rates found were: V 30 μM 0–1 h=73.8 μmol NO 3 g −1 DW h −1 and V 3 μM 0–1 h=16.7 μmol PO 4 g −1 DW h −1, in the two thinnest Porphyra. We found that the nitrate uptake rates were significantly greater at 30 μM than 3 μM NO 3 concentration, and that the uptake rates decreased with time of exposure. Temperature (5, 15, and 25 °C) did not have as strong an effect on nitrate uptake rates as did nutrient concentration. Q 10 values and uptake rates at four different nitrate concentrations indicated that nutrient uptake at 5 °C was initially an active process. After 24 h, the processes involved appeared passive as Q 10 values were between 1.0 and 1.3 and nitrate uptake curves were linear. Nitrate uptake rates correlated positively with the surface area/volume (SA/V) ratio. No coherent trends were found for uptake of phosphate, except that the uptake rates were significantly higher in 30 μM NO 3 medium as opposed to 3 μM NO 3. We did not find any significant difference in uptake rate and pattern between the summer species Porphyra purpurea (Roth.) C. Agardh, the eurythermic Porphyra suborbiculata Kjellm., the winter species Porphyra rosengurttii J. Coll and J. Cox, and the two varieties of Porphyra leucosticta Thur. Le Jol. (both winter species).

Exchange of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) between air and a mixed pasture sward.

To improve understanding of air-to-vegetation transfer of persistent organic pollutants (POPs), uptake and depuration of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) between grass sward and air was investigated. Pasture swards were placed in fanned (2 m s(-1) wind speed) and unfanned conditions for a period of 20 days and sampled at intervals. Depuration was carried out after a short (4 days) and a long (14 days) exposure period. Prior to contamination, a mixed pasture sward at a semi-rural location contained sigmaPCN concentrations 15-20% of the sigmaPCB concentration. Uptake of both PCBs and PCNs was broadly linear in fanned and unfanned conditions over the 20-day period, i.e., the pasture did not reach equilibrium with the air. Uptake rates (fluxes) were greater under the fanned conditions. The difference in uptake rates between fanned and unfanned conditions increased with degree of chlorination for both PCBs and PCNs, ranging between a factor of 2 for tri-chlorinated PCBs and PCNs and a factor 5 for octa-chlorinated PCBs. Depuration results over the first hours were very scattered, showing an initial period of loss, followed by an increase in concentrations, possibly as a result of re-volatilization of PCBs from the soil in the trays, with consequent recapture by the overlying sward. Rapid clearance was observed over the following days, but depuration of PCBs and PCNs was still incomplete after 14 days, with 20% of the initial concentration of the sigmaPCBs and 10% of the sigmaPCNs retained by the sward. There was no difference in the proportion of POPs retained in the sward between the 4- and 14-day contamination treatments. POP-specific differences in the amount of compound "trapped" in leaves after contamination were observed. The results show that, although changes in the rate of air movement around a pasture have an effect on the uptake rate of POPs into the vegetation, plant-side resistance controls both the air-to-pasture and pasture-to-air exchange of gas-phase PCBs and PCNs; i.e., differences between plant species in cuticle composition and/or structure affecting the permeability of the cuticle are of greater importance than differences in leaf morphology affecting aerodynamic roughness.

Roles of uptake, biotransformation, and target site sensitivity in determining the differential toxicity of chlorpyrifos to second to fourth instar Chironomous riparius (Meigen)

Early life stages of aquatic organisms tend to be more sensitive to various chemical contaminants than later life stages. This research attempted to identify the key biological factors that determined sensitivity differences among life stages of the aquatic insect Chironomous riparius. Specifically, second to fourth instar larvae were exposed in vivo to both low and high waterborne concentrations of chlorpyrifos to examine differences in accumulation rates, chlorpyrifos biotransformation, and overall sensitivity among instars. In vitro acetylcholinesterase (AChE) assays were performed with chlorpyrifos and the metabolite, chlorpyrifos-oxon, to investigate potential target site sensitivity differences among instars. Earlier instars accumulated chlorpyrifos more rapidly than later instars. There were no major differences among instars in the biotransformation rates of chlorpyrifos to the more polar metabolites, chlorpyrifos-oxon, and chlorpyridinol (TCP). Homogenate AChE activities from second to fourth instar larvae were refractory to chlorpyrifos, even at high concentrations. In contrast, homogenate AChE activities were responsive in a dose-dependent manner to chlorpyrifos-oxon. In general, it appeared that chlorpyrifos sensitivity differences among second to fourth instar C. riparius were largely determined by differences in uptake rates. In terms of AChE depression, fourth instar homogenates were more sensitive to chlorpyrifos and chlorpyrifos-oxon than earlier instars. However, basal AChE activity in fourth instar larvae was significantly higher than basal AChE activity in second to third instar larvae, which could potentially offset the apparent increased sensitivity to the oxon.

Pharmacokinetics of third-generation aromatase inhibitors

The latest generation of nonsteroidal aromatase inhibitors (anastrozole and letrozole) has been approved by the US Food and Drug Administration for use in the first- and second-line treatment of postmenopausal women with hormone receptor-positive (or unknown) breast cancer. The steroidal agent exemestane is approved for second-line treatment and is currently being evaluated for first line. In addition, these agents are being evaluated in the adjuvant and neoadjuvant settings. Because preclinical studies have suggested some differences in the efficacy of these agents to inhibit aromatase, it has been important to evaluate whether these properties actually translate into meaningful differences in the clinical setting. The pharmacokinetic properties of each aromatase inhibitor influences their ability to perform effectively. Examination of the data suggests differences in uptake rates, half-life of elimination, metabolism, and clearance rates that could influence their efficacy. However, the significance of these differences for clinical effectiveness over long-term use remains to be determined.

Nutrient uptake by coral-reef microatolls

We measured rates of ammonium and phosphate uptake into 12 microatolls at One Tree reef lagoon, Australia, on 14 occasions over a range of seasonal and meteorological conditions from 1993 to 1995. Nine of the microatolls were spiked with ammonia and/or phosphate every low tide (2.5–4 h) during low- (15-month) and high- (13-month) loading periods. The remaining three microatolls that were not spiked with nutrient served as reference conditions. Ammonium concentrations were elevated from an average background of 0.7 to 11 µM NH4 during the low-loading period and 36 µM NH4 during the high-loading period, resulting in a loading to the benthos of 3.5 and 18 mmol NH4 m–2 low tide–1. Phosphate concentrations were elevated from an average background of 0.2 to 2.3 and 5.1 µM PO4 during low- and high-loading periods, respectively, resulting in a loading of 0.66 and 3.9 mmol PO4 m–2 low tide–1. Ammonium and phosphate concentrations decreased significantly over low-tides, and uptake rates were proportional to concentrations (first-order). The average uptake-rate constant, S (m s–1), for ammonium and phosphate did not differ between the two loading periods but was highly variable. Averaged over both loading periods, S for ammonium was 129±74×10–6 m s–1 and S for phosphate was 67±39×10–6 m s–1. At background nutrient concentrations, estimated nutrient-uptake rates were 7.8 mmol NH4 m–2 day–1 and 1.2 mmol PO4 m–2 day–1. Excretion rates—calculated from the mean difference in uptake rates measured in reference and nutrient-enriched microatolls—were estimated to be 4.3 mmol NH4 m–2 day–1 and 0.9 mmol PO4 m–2 day–1. We reason and suggest that nutrient uptake rates in these microatolls were close to mass-transfer limited rates. We conclude that nutrient uptake into coral reefs can be highly dynamic, varying 10-fold spatially and temporally.

Contribution of explant carbohydrate reserves and sucrose in the medium to bulb growth of lily regenerated on scale segments in vitro

Bulb size is an important factor determining phase change in Lilium: phase change only occurs in bulblets over a certain threshold weight. After phase change has occurred, bulblets sprout with a stem with many leaves. Juvenile bulblets sprout with only a few leaves. The factors contributing to bulb size were studied during in vitro regeneration of bulblets on scale segments. The larger the explants, the larger the regenerated bulblets. Explant size influenced bulb growth during the complete culture period. Bulb growth was stimulated by a high sucrose concentration. The contribution of the medium and the explant reserves to bulb growth were studied in large and small explants using labelled sucrose. Sucrose was mainly taken up through the cut surfaces. In freshly cut explants, the rate of uptake was correlated with the size of the contact area, but at later stages, when regenerating organs were present, the difference in uptake rate of small and large explants almost disappeared. Small explants had a larger sink activity than large ones. Explants with regenerating organs took up more sucrose than freshly cut explants. Sucrose uptake and bulb growth were rather constant in the later phases and doubled when the sucrose concentration was doubled. Partitioning of label from the sucrose over the various organs, was also rather constant in time: approximately 25% was accumulated in the bulblets, 35–45% in the explant and 30–35% was converted to CO2. About half of the label in the explant was recovered at the proximal side where regeneration takes place. Sucrose, once incorporated in the storage pools in the explant, either remained in the explant or was converted to CO2. Redistribution to the growing bulblets hardly occurred. The percentage of bulb growth that could be attributed to uptake of medium components was constant over the regeneration period: 45–50% for large and 65–75% for small explants.

Phosphate transport in plants

Transport of inorganic phosphate (Pi) through plant membranes is mediated by a number of families of transporter proteins. Studies on the topology, function, regulation and sites of expression of the genes that encode the members of these transporter families are enabling roles to be ascribed to each of them. The Pht1 family, of which there are nine members in the Arabidopsis genome, includes proteins involved in the uptake of Pi from the soil solution and the redistribution of Pi within the plant. Members of this family are H2PO4−/H+ symporters. Most of the genes of the Pht1 family that are expressed in roots are up-regulated in P-stressed plants. Two members of the Pht1 family have been isolated from the cluster roots of white lupin. These same genes are expressed in non-cluster roots. The evidence available to date suggests that there are no major differences between the types of transport systems that cluster roots and non-cluster roots use to acquire Pi. Differences in uptake rates between cluster and non-cluster roots can be ascribed to more high-affinity Pi transporters in the plasma membranes of cluster roots, rather than any difference in the characteristics of the transporters. The efficient acquisition of Pi by cluster roots arises primarily from their capacity to increase the availability of soil Pi immediately adjacent to the rootlets by excretion of carboxylates, protons and phosphatases within the cluster. This paper reviews Pi transport processes, concentrating on those mediated by the Pht1 family of transporters, and attempts to relate those processes involved in Pi acquisition to likely Pi transport processes in cluster roots.

Patient Characteristics Determine Differences in the Influenza Vaccination Rate More so Than Practice Features

Background. World-wide each year 30–55% of the target population is vaccinated against influenza. Determinants of successful vaccination programs are not clear. This study was aimed at identifying practice- and patient-related factors that determine differences in vaccination rates. Methods. Data on patients of the target population were extracted from the computerized medical record systems of 48 family practices. Information about organizational factors was collected by a questionnaire for GP's. Multilevel logistic regression analyses were used to assess the determinants. Results. Of all patients at risk (42,426), 76% were vaccinated. The vaccination rate for patients above age 65 was 15% higher when a medical indication was present. Patients with cardiac diseases or diabetes mellitus attained a relatively higher vaccination rate than other groups at risk. Special hours for vaccination led to significantly higher vaccination rates for the elderly and cardiac patients. Patients below 65 years of age were particularly influenced by special information pamphlets. Conclusion. Explanations of differences in uptake rates were found at the patient level. All practices in this study were well organized; nevertheless, subgroup analyses showed that special vaccination hours for elderly people and information pamphlets for young people could improve results further.

Chemometric evaluation of on‐line high‐pressure liquid chromatography in mammalian cell cultures: Analysis of amino acids and glucose

An on-line high-pressure liquid chromatography (HPLC) system capable of measuring amino acids and carbohydrates was used to study metabolism in mammalian cell culture systems. The HPLC method utilized anion-exchange chromatography followed by integrated pulsed amperometric detection. The method is capable of measuring 19 amino acids plus glucose with a complete method time of 65 min. In actual cell cultures, the method was shown to be useful for monitoring 17 amino acids plus glucose. The two amino acids that were not accurately monitored were arginine and lysine, possibly due to their elution near the void volume of the column. The HPLC system was used to study variability in metabolism across different cell culture processes, as well as the effect of glucose and glutamine limitation on a single cell culture process. Chemometric analysis was used to draw statistically meaningful conclusions from the highly correlated, multivariate data set that resulted from these experiments. Using chemometrics, variation between processes was linked to differences in uptake rates of seven amino acids. Similarly, lactate concentration, cell density, and aspartate uptake rate were linked to glucose and glutamine limitation. The effect of nutrient limitation on glutamate, alanine, and ammonium was also considered.

Nitrite Concentration Effects on NO3-N Uptake and Reduction, Growth, and Fruit Yield in Strawberry

Strawberries (Fragaria xananassa Duch. 'Osogrande') were grown hydroponically with three NO3-N concentrations (3.75, 7.5, or 15.0 mM) to determine effects of varying concentration on NO3-N uptake and reduction rates, and to relate these processes to growth and fruit yield. Plants were grown for 32 weeks, and NO3-N uptake and nitrate reductase (NR) activities in roots and shoots were measured during vegetative and reproductive growth. In general, NO3-N uptake rates increased as NO3-N concentration in the hydroponics system increased. Tissue NO3- concentration also increased as external NO3-N concentration increased, reflecting the differences in uptake rates. There was no effect of external NO3-N concentration on NR activities in leaves or roots during either stage of development. Leaf NR activity averaged approximately 360 nmol NO2 formed/g fresh weight (FW)/h over both developmental stages, while NR activity in roots was much lower, averaging approximately 115 nmol NO2 formed/g FW/h. Vegetative organ FW, dry weight (DW), and total fruit yield were unaffected by NO3-N concentration. These data suggest that the inability of strawberry to increase growth and fruit yield in response to increasing NO3-N concentrations is not due to limitations in NO3-N uptake rates, but rather to limitations in NO3- reduction and/or assimilation in both roots and leaves.