Root uptake and translocation of radiocaesium from agricultural soils by various plant species

Plant uptake of radiocaesium from soil is an important pathway for the entry of this pollutant into the human food chain and so contributes to any assessment of the radiation dose following contamination. Large differences in soil–plant transfer factors have been reported for plant species grown on the same soils. Few studies have attempted to distinguish between differences in root uptake and root-to-shoot translocation. We have investigated the root uptake of radiocaesium from artificially contaminated soils and the subsequent translocation to shoots for various plant species grown on three agricultural soils. The effects of short contact times and potassium starvation or enrichment have been studied. The Cs adsorption properties of rhizosphere soils have been compared with those of the initial soils. The proportion of activity removed from soil is largely soil dependent. Root uptake properties have less effect, but appear to be species determined, and not influenced by soil properties. Differences in soil-to-shoot transfer factor arise from species-dependent differences in root-to-shoot translocation. Root-to-shoot activity ratios are not soil dependent. There was little effect of soil potassium status. Root action slightly enhanced Cs adsorption on one soil, probably due to mineral weathering associated with the release of nonexchangeable potassium.     

植物吸收利用铁的机理

根据植物铁营养的一些研究进展,论述了植物对铁的吸收和运输机理以及HCO3^-,N、P等因素对铁利用效率的影响。     

Controlling phosphate release from phosphate-enriched sediments by adding various iron compounds

In a laboratory experiment, different ironsalts (FeCl₂, FeCl₃, FeSO₄) andFe₂O₃ were added to a phosphateenriched silty loam sediment in order to studytheir effect on phosphate mobilisation.Phosphate concentrations in sediment pore waterwere not reduced by the addition ofFe₂O₃. Addition of both ironchlorides, however, resulted in a strongdecrease of phosphate levels in sediment porewater. A similar but less pronounced effect wascaused by the addition of iron as iron(II)sulphate. Sulphate appears to counteract theimmobilisation of phosphate brought about byiron(II). Phosphate release from the sedimentappeared to be determined by the iron/phosphateratio in the sediment pore water. The additionof Fe₂O₃ barely affected thephosphate release from the sediment whereas theaddition of iron salts was effective inpreventing phosphate release. Increased amountsof iron added to the sediment resulted in adecreased phosphate release.     

Root-microbial effects on plant iron uptake from siderophores and phytosiderophores

Collaborative experiments were conducted to determine whether microbial populations associated with plant roots may artifactually affect the rates of Fe uptake and translocation from microbial siderophores and phytosiderophores. Results showed nonaxenic maize to have 2 to 34-fold higher Fe-uptake rates than axenically grown plants when supplied with 1 μM Fe as either the microbial siderophore, ferrioxamine B (FOB), or the barley phytosiderophore, epi-hydroxymugineic acid (HMA). In experiments with nonsterile plants, inoculation of maize or oat seedlings with soil microorganisms and amendment of the hydroponic nutrient solutions with sucrose resulted in an 8-fold increase in FOB-mediated Fe-uptake rates by Fe-stressed maize and a 150-fold increase in FOB iron uptake rates by Fe-stressed oat, but had no effect on iron uptake by Fe-sufficient plants. Conversely, Fe-stressed maize and oat plants supplied with HMA showed decreased uptake and translocation in response to microbial inoculation and sucrose amendment. The ability of root-associated microorganisms to affect Fe-uptake rates from siderophores and phytosiderophores, even in short-term uptake experiments, indicates that microorganisms can be an unpredictable confounding factor in experiments examining mechanisms for utilization of microbial siderophores or phytosiderophores under nonsterile conditions.     

Association of polyamines to different parts of various plant species

The variation in polyamine content in different plant species and in different parts within a plant can be considerable. To get general information about levels of polyamines in plants and about the association of polyamines to different types of tissue, 30 plants from 13 plant families were examined for their polyamine content before and after germination using high pressure liquid chromatography (HPLC) analysis. A marked increase in polyamine content occurs in the cotyledons or endosperms in the seeds on germination, i.e. in the nutrient storing and exporting part of the plant. In the radicle, hypocotyl or coleoptile, i.e. growing parts of the plant, an increase in polyamine content is rarely observed. Additionally, polyamine levels can be very low [below 1 nmol (g fresh weight)^-1] in different parts of various species. Obviously, levels in the pmol (g fresh weight)^-1 range satisfy the needs of many growing plant parts. The high levels of polyamines found especially in cotyledons cannot be explained by their postulated association with increased cell division rates.     

Iron and gallium increase iron uptake from transferrin by human melanoma cells: further examination of the ferric ammonium citrate-activated iron uptake process

Previously we showed that preincubation of cells with ferric ammonium citrate (FAC) resulted in a marked increase in Fe uptake from both (59)Fe-transferrin (Tf) and (59)Fe-citrate (D.R. Richardson, E. Baker, J. Biol. Chem. 267 (1992) 13972-13979; D.R. Richardson, P. Ponka, Biochim. Biophys. Acta 1269 (1995) 105-114). This Fe uptake process was independent of the transferrin receptor and appeared to be activated by free radicals generated via the iron-catalysed Haber-Weiss reaction. To further understand this process, the present investigation was performed. In these experiments, cells were preincubated for 3 h at 37 degrees C with FAC or metal ion solutions and then labelled for 3 h at 37 degrees C with (59)Fe-Tf. Exposure of cells to FAC resulted in Fe uptake from (59)Fe-citrate that became saturated at an Fe concentration of 2.5 microM, while FAC-activated Fe uptake from Tf was not saturable up to 25 microM. In addition, the extent of FAC-activated Fe uptake from citrate was far greater than that from Tf. These results suggest a mechanism where FAC-activated Fe uptake from citrate may result from direct interaction with the transporter, while Fe uptake from Tf appears indirect and less efficient. Preincubation of cells with FAC at 4 degrees C instead of 37 degrees C prevented its effect at stimulating (59)Fe uptake from (59)Fe-Tf, suggesting that an active process was involved. Previous studies by others have shown that FAC can increase ferrireductase activity that may enhance (59)Fe uptake from (59)Fe-Tf. However, there was no difference in the ability of FAC-treated cells compared to controls to reduce ferricyanide to ferrocyanide, suggesting no change in oxidoreductase activity. To examine if activation of this Fe uptake mechanism could occur by incubation with a range of metal ions, cells were preincubated with either FAC, ferric chloride, ferrous sulphate, ferrous ammonium sulphate, gallium nitrate, copper chloride, zinc chloride, or cobalt chloride. Stimulation of (59)Fe uptake from Tf was shown (in order of potency) with ferric chloride, ferrous sulphate, ferrous ammonium sulphate, and gallium nitrate. The other metal ions examined decreased (59)Fe uptake from Tf. The fact that redox-active Cu(II) ion did not stimulate Fe uptake while redox-inactive Ga(III) did, suggests a mechanism of transporter activation not solely dependent on free radical generation. Indeed, the activation of Fe uptake appears dependent on the presence of the Fe atom itself or a metal ion with atomic similarities to Fe (e.g. Ga).     

植物对羰基化合物的排放与吸收研究进展

综述了植物排放、吸收羰基化合物的研究成果,讨论了植物与大气之间羰基化合物的交换补偿点问题.气孔和角质层的吸收是醛类被植物净化的重要途径.羰基化合物进入植物叶片后,在叶片体内酶的作用下绝大部分被代谢为有机酸、糖类、氨基酸、二氧化碳等产物.根据补偿点及周围大气中羰基化合物的浓度可初步推断出植物与大气之间羰基化合物的交换方向.简要叙述了目前植物排放羰基化合物以及植物叶片中羰基化合物的分析方法,如DNPH/HPLC/UV和PFPH/GC/MS法.最后指出未来的研究热点为:改进和优化植物排放羰基化合物的分析方法和研究体系(如植物-土壤体系)、扩大植物排放羰基化合物的检测种类范围、筛选净化污染能力强的植物物种,以及推广植物修复大气污染技术.     

Utilization of phosphate from different sources by six plant species

Summary Six plant species, wheat, paspalum grass (Paspalum plicatulum), maize, molasses grass (Melinis minutiflora), soybean and buckwheat (Fagopyrum esculentum) were compared for their abilities to utilize phosphate from superphosphate, a calcined aluminum phosphate and four rock phosphates.Buckwheat showed an exceptional behaviour in that it could utilize all phosphates. For the other plants, only the calcined aluminum phosphate and one rock phosphate (hyperphosphate) had significant fertilizing values. Their efficiencies, relative to superphosphate, were 0.45 and 0.11 for wheat, 0.73 and 0.43 for paspalum grass, 0.50 and 0.37 for maize, 0.46 and 0.42 for molasses grass, 0.28 and 0.38 for soybean, and 0.72 and 1.08 for buckwheat, respectively.For three P sources, superphosphate, calcined aluminum phosphate and hyperphosphate, a relationship between soil acidity and P uptake was found. Soil pH in its turn was negatively related to the ratio of total equivalents of cations and those of anions absorbed. Consequenly, P uptake was positively related to the ratio of total equivalents of cations to those of anions absorbed. The same effect of plant species on soil pH could also explain the difference in uptake of P from sparingly soluble phosphates. The relative efficiencies of calcined aluminum phosphate and hyperphosphate for the various plant species were closely related to the ratio of total cations and total anions absorbed by these plants.on leave at the Agricultural University during 1977.     

Iron uptake from ferrichrome A and iron citrate in Ustilago sphaerogena.

Double radioactive label transport assays with iron, chromium, and gallium chelates were used to investigate the mechanism of iron uptake by Ustilago sphaerogena. In iron-deficient cells, ferrichrome A iron was taken up without appreciable uptake of the ligand. Iron-sufficient cells partially accumulated the ligand with the metal. The chromium- and gallium-containing analogs of ferrichrome A were transported as intact chelates. Ferrichrome A iron uptake was inhibited by dipyridyl. The data suggest that the intact ferrichrome A chelate binds to a specific receptor, the iron is then separated from the ligand at the membrane by reduction, and the metal is released to the inside of the cell while the ligand is released to the exterior. The reduction step is not transport rate limiting. Iron chelated to citrate was taken up by an energy-dependent process. The citrate ligand was not taken up with the metal. Uptake was sensitive to dipyridyl and ferrozine. Chromic ion chelated to citrate was not transported, suggesting that the iron, rather than the chelate, is recognized by the receptor or that reduction of the metal is required for transport.     

Papillomavirus capsid binding and uptake by cells from different tissues and species.

The inability of papillomaviruses (PV) to replicate in tissue culture cells has hampered the study of the PV life cycle. We investigated virus-cell interactions by the following two methods: (i) using purified bovine PV virions or human PV type 11 (HPV type 11) virus-like particles (VLP) to test the binding to eukaryotic cells and (ii) using different VLP-reporter plasmid complexes of HPV6b, HPV11 L1 or HPV11 L1/L2, and HPV16 L1 or HPV16 L1/L2 to study uptake of particles into different cell lines. Our studies showed that PV capsids bind to a broad range of cells in culture in a dose-dependent manner. Binding of PV capsids to cells can be blocked by pretreating the cells with the protease trypsin. Penetration of PV into cells was monitored by using complexes in which the purified PV capsids were physically linked to DNA containing the gene for beta-galactosidase driven by the human cytomegalovirus promoter. Expression of beta-galactosidase occurred in < 1% of the cells, and the efficiency of PV receptor-mediated gene delivery was greatly enhanced (up to 10 to 20% positive cells) by the use of a replication-defective adenovirus which promotes endosomal lysis. The data generated by this approach further confirmed the results obtained from the binding assays, showing that PV enter a wide range of cells and that these cells have all functions required for the uptake of PV. Binding and uptake of PV particles can be blocked by PV-specific antisera, and different PV particles compete for particle uptake. Our results suggest that the PV receptor is a conserved cell surface molecule(s) used by different PV and that the tropism of infection by different PV is controlled by events downstream of the initial binding and uptake.     

Preferential uptake of soil nitrogen forms by grassland plant species

In this study, we assessed whether a range of temperate grassland species showed preferential uptake for different chemical forms of N, including inorganic N and a range of amino acids that commonly occur in temperate grassland soil. Preferential uptake of dual-labelled (¹³C and ¹⁵N) glycine, serine, arginine and phenylalanine, as compared to inorganic N, was tested using plants growing in pots with natural field soil. We selected five grass species representing a gradient from fertilised, productive pastures to extensive, low productivity pastures (Lolium perenne, Holcus lanatus, Anthoxanthum odoratum, Deschampsia flexuosa, and Nardus stricta). Our data show that all grass species were able to take up directly a diversity of soil amino acids of varying complexity. Moreover, we present evidence of marked inter-species differences in preferential use of chemical forms of N of varying complexity. L. perenne was relatively more effective at using inorganic N and glycine compared to the most complex amino acid phenylalanine, whereas N. stricta showed a significant preference for serine over inorganic N. Total plant N acquisition, measured as root and shoot concentration of labelled compounds, also revealed pronounced inter-species differences which were related to plant growth rate: plants with higher biomass production were found to take up more inorganic N. Our findings indicate that species-specific differences in direct uptake of different N forms combined with total N acquisition could explain changes in competitive dominance of grass species in grasslands of differing fertility.     

Root colonization and iron nutritional status of a Pseudomonas fluorescens in different plant species

Root colonization and induction of an iron stress regulated promoter for siderophore production by Pseudomonas fluorescens 2-79RLI was studied in vitro and in the rhizosphere of different plant species. P. fluorescens 2-79RLI was previously genetically modified with an iron regulated ice nucleation reporter, which allowed calibration of ice nucleation activity with siderophore production. Initial experiments examined ice nucleation activity and siderophore production under different growth conditions in vitro. These studies demonstrated that P. fluorescens 2-79RLI could utilize both Fe-citrate and Fe-phytosiderophore as iron sources, suggesting that production of these compounds by plants would increase iron availability for P. fluorescens 2-79RLI in the rhizosphere. Fe demand and Fe stress were further shown to be a function of nutrient availability and were reduced when carbon was limiting for growth. Subsequent experiments extended these observations to rhizosphere cells. Cells were sampled from the rhizosphere and the rhizoplane. Results of a soil microcosm experiment showed that Fe stress was reduced for P. fluorescens 2-79RLI in the barley rhizosphere as compared to the cells in the rhizosphere.of lupin. In lupin, relative Fe stress of P. fluorescens 2-79RLI was greater at the root tip than in the lateral root zone. In a second experiment comparing zucchini and bean, iron stress was greater for P. fluorescens 2-79RLI associated with zucchini than with bean. In a third experiment with rape plants under P deficient conditions, addition of soluble P was shown to increase Fe stress for P. fluorescens 2-79RLI located at the root tip, but not in the lateral root zone. This study showed that Fe stress of P. fluorescens 2-79RLI in the rhizosphere may be influenced by plant species, P source, root zone and localization of the cells within the rhizosphere.     

Iron uptake from sialo transferrins by rat reticulocytes

Preparative isoelectric focusing of human diferric transferrin preparations yielded seven bands with different isoelectric points, due to differences in sialic acid content. Incubation of rat reticulocytes at 37 and 4 degrees C with differic preparations of four of these transferrin forms labeled with 59Fe and 125I show no differences in membrane binding of iron and transferrin and in iron uptake. Hence it is concluded that the carbohydrate chains are not directly involved in the process of iron delivery to reticulocytes.     

Metal uptake by different species of phytoplankton in culture

Cadmium and copper uptake by cultures of Prasinocladus marinus, Amphidinium carterae, Chaetoceros curvisetum and Chaetoceros protuberans was considered as a function of exposure time (from 0.5 to 72 h) and of metal concentrations added to the culture medium (from 5 to 20 µg l^–1). For cadmium uptake, A. carterae exhibited a particular behaviour: the accumulation was not dependent on exposure time or on metal concentration. An adsorption process appeared to govern both Cadmium uptake by phytoplankton species (except A. carterae) and that of copper. In addition to adsorption, another active process might be involved in the Cadmium uptake of P. marinus, C. curvisetum and C. protuberans.     

Comparison of plant uptake and plant toxicity of various ions in wheat

The effects of varying solution concentrations of manganese (Mn), zinc (Zn), copper (Cu), boron (B), iron (Fe), gallium (Ga) and lanthanum (La) on plant chemical concentrations, plant uptake and plant toxicity were determined in wheat (Triticum aestivum L.) grown in a low ionic strength (2.7×10^–3 M solution culture). Increasing the solution concentration of Mn, Zn, Cu, B, Fe, Ga and La increased plant concentrations of that ion. Asymptotic maximum plant concentrations were reached for Zn (10 mg kg DM^–1 in the roots), Ga (2 mg kg DM^–1 in the tops and 18 mg kg DM^–1 in the roots) and La (0.4 mg kg DM^–1 in the tops and 4 mg kg DM^–1 in the roots). Plant ion concentrations were, on average, 3 times higher in the roots than the tops for Mn and Zn, 7 times for Cu, 9 times for Fe, 12 times for Ga and 15 times for La. In contrast, B concentrations were higher in the tops than the roots by, on average, 2 times. The estimated toxicity threshold (plant concentration at which a rapid decrease in yield occurred) in the tops was 0.4 mg g DM^–1 for B, 2 for Zn, 0.075 for Cu and 0.09 for La and in the roots 0.2 mg g DM^–1 for B, 5 for Zn, 0.3 for Cu and 3 for La. Plant uptake rates of the ions (as estimated by the slope of the relationship between solution ion concentrations and plant ion concentrations) was in the order B 250 mg kg DM^–1 M ^–1). Plant toxicity was estimated as the reciprocal of the plant concentration that reduced yield by 50% (change in relative yield per mg ion kg DM^–1). The plant toxicity of the ions tested was in the order Mn相似文献   

Iron uptake from ferric citrate by Vibrio anguillarum

We report here that Vibrio anguillarum possesses a non-inducible active transport system which can efficiently supply iron to the cell from ferric citrate, independently of the siderophore-based mechanisms. The strains tested were able to grow in CM9 medium in iron-restricted conditions when ferric citrate was present in the medium. Moreover, the presence of ferric citrate inhibited the production of siderophores in the strains tested. V. anguillarum cells and isolated membranes could incorporate ⁵⁵Fe³⁺ complexed by citrate, without a difference between cells grown in the presence or absence of ferric citrate. The presence of 2,4-dinitrophenol, ferrozine, ferricyanide, trypsin, as well as low temperature produced a marked decrease or total inhibition of ⁵⁵Fe³⁺ uptake by the cells. All these results suggest that iron uptake from ferric citrate in V. anguillarum must be an energy-dependent process not induced by the presence of iron or citrate in the medium, mediated by a membrane protein(s), which may require an iron reduction step to function.