Characterization of cadmium uptake by the water lily Nymphaea aurora

This study characterizes cadmium (Cd) uptake by the waterlily Nymphaea aurora, (Nymphaeaceae) in two systems: a model hydroponic Cd solution and heavily polluted sludge from two sites in Israel. The uptake of Cd from hydroponic solution resulted in Cd storage in petioles and laminae of Nymphaea, as well as in the roots. The pH of the solution affected Cd solubility and availability, with pH 5.5 yielding maximum Cd content in the plant (140 mg Cd per g DW). Cd uptake was reduced by the addition of EDTA to the hydroponic growth medium, although EDTA enhanced heavy metal uptake by terrestrial plants. Nymphaea efficiently reduced the concentration of Cd in heavy metal polluted urban and industrial sludge and the amount of Cd uptake was enhanced by the addition of KCl to the sludge and by adjustment of the pH to 5.5. The inherent growth patterns of Nymphaea plants allowed Cd uptake by the shoot and root, and resulted in maximum contact between the various plant parts and the growth media. Thus, Nymphaea has potential as an optimal, highly effective phytoremediation tool for the removal of Cd from polluted waste sources.     

Phytotransformation of 2,4-dinitrotoluene in arabidopsis thaliana: toxicity, fate, and gene expression studies in vitro

Basic knowledge of the plant transformation pathways and toxicity of 2,4-dinitrotoluene (2,4-DNT) will assist in the design and assessment of a phytoremediation strategy. This study presents the toxicity and fate of 2,4-DNT and gene expression in response to 2,4-DNT exposure using the model plant Arabidopsis thaliana, an increasingly popular system for genetic and biochemical studies of phytotransformation of explosives. From the results of biomass and root growth assays for toxicity, 2,4-DNT was toxic to the plants at concentrations as low as 1 mg/L. In the uptake study, 95% of the initial 2,4-DNT was removed by 15-day-old seedlings from liquid media regardless of the initial 2,4-DNT concentrations while 30% accounted for the adsorption to the autoclaved plant materials. The mass balance was over 86% using [U-14C]2,4-DNT, and the mineralization by the plants was less than 1% under sterile conditions during 14 days of exposure. The percentage of the bound radioactivity increased from 49% to 72% of the radioactivity in the plants, suggesting transformed products of 2,4-DNT may be incorporated into plant tissues such as lignin and cellulose. Monoaminonitrotoluene isomers and unknown metabolites with short retention times were detected as transformed products of 2,4-DNT by the plants. Most (68%) of the radioactivity taken up by the plants was in the root tissues in nonsterile hydroponic cultures. Glutathione and expression of related genes (GSH1 and GSH2) in plants exposed to 2,4-DNT were 1.7-fold increased compared to untreated plants. Genes of a glutathione S-transferase and a cytochrome P450, which were induced by 2,4,6-trinitrotoluene exposure in previous studies, were upregulated by 10- and 8-fold, respectively. The application of phytoremediation and the development of transgenic plants for 2,4-DNT may be based on TNT phytotransformation pathway characteristics because of the similar fate and gene expression in plants.     

Interactive effects of pH, arsenic and phosphorus on uptake of As and P and growth of the arsenic hyperaccumulator Pteris vittata L. under hydroponic conditions

Arsenic (As)-contaminated soil and water vary with pH and concentrations of As and P. This study examined the effects and interactions of three factors, pH, As and P, on As hyperaccumulator Pteris vittata L. to optimize plant growth and maximize As removal from contaminated sites, especially water. Two sets of hydroponic experiments were conducted using three-factor, five-level central composite design. Five levels of pH (4.5–8.0), As (0–668 μM), and P (0–1000 μM) were used to understand their individual as well as interactive effects. Plant biomass and uptake of P and As were impacted by all the three factors. Phosphorus inhibited As uptake at all concentrations, whereas As below 334 μM benefited plant growth and P uptake. Enhanced plant biomass was most likely a result of increased P uptake. Low pH enhanced plant uptake of As (pH≤5.21) and P (pH≤6.25). The fern had a relatively high biomass and P uptake at low pH/low As or high pH/high As. The referencing saddle points (turning points) were pH 6.33 and As 359 μM for plant biomass and pH 5.87 and As 331 μM for P uptake based on the response surface plot. The results suggested that optimum plant growth could be achieved by adjusting pH corresponding to As levels in the growth media, and maximum plant As hyperaccumulation by maintaining minimum P concentrations with medium pH≤5.21. Our results should be useful for developing strategies to remediate As-contaminated water using Chinese Brake fern.     

Phytotransformation of benzotriazoles

Plant roots interact with organic pollutants and some of these contaminants can be phytotransformed. Root uptake of 1-H-benzotriazole and its derivatives, tolyltriazole, 5-methyl benzotriazole, and 1-hydroxy benzotriazole was studied. At levels below the toxic threshold of about 100 mg/L, triazoles appear to be incorporated into plant tissue. Their concentration in the aqueous phase of the culture decreases with time and they cannot be extracted from the plant material using methanol. Hydroponic studies with sunflowers (Helianthus annuus) were used to investigate the behavior of the solution concentration versus time and to determine kinetic parameters for plant uptake of triazoles. Plants actively take up the triazoles at a rate greater than predicted by transpiration stream-concentration factor and plant-water uptake. Analyses of the data for phytotransformation rate versus concentration were performed to establish the kinetic model for the removal process. Except for 1-hydroxy-benzotriazole, triazole disappearance in plant systems followed the Michaelis-Menten kinetic model (commonly found for enzyme-catalyzed reactions) better than a first order rate model. However, the fit for the first order model was improved when normalizing to the plant fresh weight, which was assumed to be an approximate measure of the changing root surface area. Experiments with other plant species are in progress.     

Sequestration,Phytoreduction, and Phytooxidation of Halogenated Organic Chemicals by Aquatic and Terrestrial Plants

Laboratory data from plant-mediated transformation of chlorinated and brominated alkanes, alkenes, and chlorinated pesticides, including phytotransformation data from field plants currently used in phytoremediation of trichloroethylene (TCE), were reviewed for the purpose of identifying important phytoprocesses and their respective roles in phytoremediation of halogenated organic compounds (HOCs). The results of the laboratory experiments indicated that the initial very rapid removal of hydrophobic HOCs from water or the gas phase by aquatic and terrestrial plants is primarily due to sequestration. The amount of HOC sequestered is controlled by the plant species and the physicochemical properties (e.g., K_ow, aqueous solubility, volatility) of the contaminant. Phytodegradation studies conducted in both the gas and aqueous phases indicated that hexachloroethane (HCA) is dechlorinated to the same metabolites by sterilized and axenically cultivated aquatic plants and an isolated plant dehalogenase factor. Similar results were obtained in experiments conducted with o,p'-DDT and p,p'-DDT in aqueous solution. The sterilized and axenically cultivated aquatic plants also oxidized HCA to similar chloroacetic acids. The metabolism of HOCs to the corresponding oxidative and reductive transformation products identified in the plant rhizosphere, stems, and leaves suggested that more than one pathway, requiring different enzymes, may be involved in phytotransformation reactions. Four phytoprocesses (mechanisms) were found to be important in the removal of the probe HOCs from water by aquatic plants, namely, (1) rapid sequestration by partitioning to the lipophilic plant cuticles; (2) phytoreduction to less halogenated metabolites; (3) phytooxidation to haloethanols, haloacetic acids, and unidentified metabolites; and (4) assimilation into the plant tissues as nonphytotoxic products, presumably produced by covalent binding with the plant tissues. Laboratory and field data indicate that the distribution of metabolites of perchloroethylene (PCE) and TCE in cottonwood and willow trees is determined by the growth stage or age of these vascular plants, the plant species, and the duration of exposure to the compound. For terrestrial plants, the predominant phytoprocesses by which HOCs are attenuated in the environment include sequestration, rhizodegradation, uptake, phytodegradation, and phytovolatilization. Using PCE as a model chlorinated organic solvent, possible phytotransformation pathways are proposed to account for the different metabolites identified in the rhizosphere and tissues of laboratory and field plants. The proposed pathways also combine phytoreduction reactions that occur in plant tissues and are likely catalyzed by plant dehalogenase(s) for example, enzyme(s) such as glutathione-S-transferase and Fe-S clusters in chloroplast ferredoxin, with phytooxidation and covalent binding (phytoassimilation) reactions mediated by oxidative-enzymes (possibly cytochrome P-450 with monooxygenase activity, glutathione or laccase). Depending on the characteristics of the field site, the phytoprocesses identified in this study are vital in the design and implementation of phytoremediation of halogenated organic contaminants.     

柳树对亚铁氰化物的吸收、代谢及其毒性研究

为探明亚铁氰化物在植物体内的迁移、转化及对植物的毒性作用,以长出新根须和嫩叶的垂柳(SalixbabylonicaL.)枝条为材料,在自行设计的250ml生物反应器中生长192h,培养温度为24.0±1℃,亚铁氰化物水溶液的浓度分别为52.99,105.98,211.95和317.93mgCNL-1。结果表明:(1)低浓度实验组(52.99mgCNL-1)水溶液中10.85%的亚铁氰化物被植物吸收,随着浓度的升高吸收到植物体内的亚铁氰化物的比例(%)依次递减,但是统计学分析显示各实验组单位体重(湿重)的植物吸收亚铁氰化物的量无显著性差异;(2)在植物的各个部位都能检测到微量的亚铁氰化物,表明亚铁氰化物通过植物的蒸腾作用在植物体内的迁移。由于没有检测到在气态下的总氰化物,表明植物的蒸腾作用没有将亚铁氰化物释放到大气中;(3)尽管植物吸收到体内的亚铁氰化物是有限的,但物质平衡实验证明其在植物体内迁移的过程中超过96%的都能被植物有效转化;(4)所用的4种亚铁氰化物浓度在192h内没有对柳树产生毒性作用。因此认为:依据亚铁氰化物在水溶液→植物→空气系统内的迁移和转化,亚铁氰化物的植物修复是可能的。     

Ammonium Nutrition as a Strategy for Cadmium Mobilisation in the Rhizosphere of Sunflower

Ammonium nutrition of higher plants results in rhizosphere acidification due to proton excretion by root cells. The acidification induced by ammonium-fed plants can be exploited to promote a localised metal mobilisation in neutral to alkaline polluted soils and therefore to improve phytoextraction. The effects of ammonium uptake by sunflower (Helianthus annuus L.) plants on the external medium pH, aerial and root growth and tolerance to soluble Cd were studied in hydroponic culture. The ammonium-fed sunflowers induced a strong acidification of the solution and, compared to the nitrate-fed sunflowers, a small modification in mineral nutrition and a different Cd partitioning between root and shoot. Moreover, ammonium nutrition was found to induce a great mobilisation of a sparingly soluble form of cadmium (CdCO₃). A pot experiment studied the ability of different ammonium-based fertilisers (ammonium sulphate, ammonium thiosulphate, urea) to modify bulk and rhizo-soil pH, compared to the effect of calcium nitrate and to the unfertilised soil. Furthermore, in order to promote the persistence of ammonium in soil, a combined treatment of ammonium sulphate and DMPP, a nitrification inhibitor, was tested. Soil pH was strongly modified by chemical and biological processes involved in fertiliser transformations. In particular, due to nitrification, all ammonium-based treatments showed a bulk soil acidification of over 1.5 pH units and a relative increase in rhizo-soil pH as a consequence of nitrate uptake. The treatment with DMPP showed an opposite trend with a lower pH in rhizo-soil than in bulk soil. The ability of ammonium-fed plants to mobilise heavy metals from the non-labile pool was studied in another pot experiment using three soils with different properties and at different degree and type of heavy metal contamination. Whatever the soil, the metal concentrations in shoots were higher in plants fed with ammonium (ammonium sulphate plus DMPP treatment). Our results support the hypothesis that ammonium nutrition with nitrification inhibitors is a viable strategy to improve heavy metals phytoextraction while protecting bulk soil from acidification and presumably from metal leaching. An erratum to this article is available at .     

Plant-Uptake of Uranium: Hydroponic and Soil System Studies

Limited information is available on screening and selection of terrestrial plants for uptake and translocation of uranium from soil. This article evaluates the removal of uranium from water and soil by selected plants, comparing plant performance in hydroponic systems with that in two soil systems (a sandy-loam soil and an organic-rich soil). Plants selected for this study were Sunflower (Helianthus giganteus), Spring Vetch (Vicia sativa), Hairy Vetch (Vicia villosa), Juniper (Juniperus monosperma), Indian Mustard (Brassica juncea), and Bush Bean (Phaseolus nanus).

Plant performance was evaluated both in terms of the percent uranium extracted from the three systems, as well as the biological absorption coefficient (BAC) that normalized uranium uptake to plant biomass. Study results indicate that uranium extraction efficiency decreased sharply across hydroponic, sandy and organic soil systems, indicating that soil organic matter sequestered uranium, rendering it largely unavailable for plant uptake. These results indicate that site-specific soils must be used to screen plants for uranium extraction capability; plant behavior in hydroponic systems does not correlate well with that in soil systems. One plant species, Juniper, exhibited consistent uranium extraction efficiencies and BACs in both sandy and organic soils, suggesting unique uranium extraction capabilities.     

Uptake and transport of N,P and K in tomato supplied with nettle water and nutrient solution

Water extract of stinging nettle (Urtica dioica) has a growth stimulating effect on plants. This investigation elucidated effects of nettle water on uptake and transport of N, P and K. Tomato plants (Solanum lycopersicum L. cv. Dansk export) were grown in sand culture 6–8 weeks. Plants were supplied with nettle water and nutrient solution was used as a control medium. Uptake and transport of N, P and K⁺ were determined with isotopes (¹⁵N,³²P and⁸⁶Rb⁺ as a tracer for K⁺) and ion-selective electrodes and in exudation experiments. A 15% higher uptake of nitrogen (¹⁵N assay) was found after nettle water treatment compared with the nutrient solution control. The total amount of nitrogen was also higher in plants cultivated with nettle water. Transport of inorganic and organic nitrogen, measured in exudation experiments, was more than 50% higher for plants supplied with nettle water compared with plants supplied with nutrient solution. In contrast, nettle water had no effect on uptake, transport or total amount of phosphorus and potassium in the plants. Experiments in hydroculture showed that nettle water had a strong pH-elevating effect. Uptake of NH ₄ ⁺ was strongly stimulated by nettle water compared with nutrient solution. By holding pH at a constant level during the uptake period for 6 h, the uptake of NH ₄ ⁺ from nettle water was significantly lower when no adjustment of pH was made. Consequently a good deal of the NH ₄ ⁺ uptake enhancement by nettle water could be explained by pH-stimulation. Assays with the uncoupler/inhibitor 2,4-dinitrophenol (DNP) and dichlorophenyl-dimethyl-urea (DCMU) showed that uptake of nitrogen from nettle water was less metabolically-linked than uptake from a corresponding nutrient solution. All together, nettle water seems to stimulate the uptake of nitrogen, but not phosphorus or potassium.     

Effects of ionic and complexed metal concentrations on plant uptake of cadmium and micronutrient metals from solution

Summary Uptake of Cd and micronutrient metals by intact tomato plants (Lycopersicon esculentum, cv. Wisconsin-55) from solution cultures was investigated by establishing four levels of Cd-ion activity in the presence or absence of a metal-complexing agent (±EDTA). Activity ratios of Cd, Cu, Mn, Ni, and Zn were controlled with chelating resin while activity ratios of K, Ca, and Mg were controlled with a strong-acid cation-exchange resin. Hydrogen ion activity was controlled with a weak-acid cation-exchange resin and P activity by a cation-exchange resin containing adsorbed polynuclear hydroxy-Al. The concentrations of all nutrients and Cd were maintained at concentrations similar to those occuring in solutions of sludge-amended soils. The EDTA treatments increased the concentrations of Cu and Ni in hydroponic solution by approximately four orders of magnitude, Zn by two orders of magnitude, Cd by a factor of 50, Mn by a factor of 2.4, and Fe by a factor of 1.6 Neither the Cd nor the EDTA treatments affected plant yield, and Cd treatments did not significantly affect uptake of other elements. EDTA treatments inhibited Fe uptake, enhanced Cu uptake, and had little effect on the uptake of Cd, Zn, and Mn. Accumulation of Cd, Zn, Mn, and Cu in plant shoots appears to be related to their respective ionic activities rather than their concentrations in hydroponic solution. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and by the United States Environmental Protection Agency through Grant CR807270010.     

Effects of root medium pH on root water transport and apoplastic pH in red‐osier dogwood (Cornus sericea) and paper birch (Betula papyrifera) seedlings

• Soil pH is a major factor affecting plant growth. Plant responses to pH conditions widely vary between different species of plants. However, the exact mechanisms of high pH tolerance of plants are largely unknown. In the present study, we compared the pH responses of paper birch (Betula papyrifera) seedlings, a relatively sensitive species to high soil pH, with red‐osier dogwood (Cornus sericea), reported to be relatively tolerant of high pH conditions. We examined the hypotheses that tolerance of plants to high root zone pH is linked to effective control of root apoplastic pH to facilitate nutrient and water transport processes
• In the study, we exposed paper birch and red‐osier dogwood seedlings for six weeks to pH 5, 7 and 9 under controlled‐environment conditions in hydroponic culture. Then, we measured biomass, gas exchange, root hydraulic conductivity, ferric chelate reductase (FCR) activity, xylem sap pH and the relative abundance of major elements in leaf protoplasts and apoplasts.
• The study sheds new light on the rarely studied high pH tolerance mechanisms in plants. We found that compared with paper birch, red‐osier dogwood showed greater growth, higher gas exchange, and maintained higher root hydraulic conductivity as well as lower xylem sap pH under high pH conditions.
• The results suggest that the relatively high pH tolerance of dogwood is associated with greater water uptake ability and maintenance of low apoplastic pH. These traits may have a significant impact on the uptake of Fe and Mn by leaf cells.

     

Uptake of 5 9Fe from soluble 5 9Fe-humate complexes by cucumber and barley plants

The capability of cucumber (Cucumis sativus L., cv. Serpente cinese), a Strategy I plant and barley (Hordeum vulgaris L., cv. Europa), a Strategy II plant to use Fe complexed by a water-soluble humic fraction (WEHS) extracted from a peat, was studied. Uptake of ⁵⁹Fe from ⁵⁹Fe-WEHS by cucumber plants was higher at pH 6.0 than at pH 7.5. Roots of intact cucumber plants were able to reduce the Fe^III-WEHS complex either at pH 6.0 or 7.5, rates being higher in the assay medium buffered at pH 6.0. After supply of ⁵⁹Fe-WEHS, a large pool of root extraplasmatic ⁵⁹Fe was formed, which could be used to a large extent by Fe-deficient plants, particularly under acidic conditions. Uptake of ⁵⁹Fe from ⁵⁹Fe-WEHS by Fe-sufficient and Fe-deficient barley plants was examined during periods of high (morning) and low (evening) PS release. Uptake paralleled the diurnal rhythm of PS release. Furthermore, ⁵⁹Fe uptake was strongly enhanced by addition of PS to the uptake solution in both Fe-sufficient and Fe-deficient plants. High amount of root extraplasmatic ⁵⁹Fe was formed upon supply of Fe-WEHS, particularly in the evening experiment. Fe-deficient barley plants were able to utilize Fe from the root extraplasmatic pool, conceivably as a result of high rates of PS release. The results of the present work together with previous observations indicate that cucumber plants (Strategy I) utilize Fe complexed to WEHS, presumably via reduction of Fe^III-WEHS by the plasma membrane-bound reductase, while barley plants (Strategy II) use an indirect mechanism involving ligand exchange between WEHS and PS.     

Solubilisation of Phosphate and Micronutrients by Trichoderma harzianum and Its Relationship with the Promotion of Tomato Plant Growth

Trichoderma harzianum strain SQR-T037 is a biocontrol agent that has been shown to enhance the uptake of nutrients (macro- and microelements) by plants in fields. The objective of this study was to investigate the contribution of SQR-T037 to P and microelement (Fe, Mn, Cu and Zn) nutrition in tomato plants grown in soil and in hydroponic conditions. Inoculation with SQR-T037 significantly improved the biomass and nutrient uptake of tomato seedlings grown in a nutrient-limiting soil. So we investigated the capability of SQR-T037 to solubilise sparingly soluble minerals in vitro via four known mechanisms: acidification by organic acids, chelation by siderophores, redox by ferric reductase and hydrolysis by phytase. SQR-T037 was able to solubilise phytate, Fe₂O₃, CuO, and metallic Zn but not Ca₃(PO₄)₂ or MnO₂. Organic acids, including lactic acid, citric acid, tartaric acid and succinic acid, were detected by HPLC and LC/MS in two Trichoderma cultures. Additionally, we inoculated tomato seedlings with SQR-T037 using a hydroponic system with specific nutrient deficiencies (i.e., nutrient solutions deficient in P, Fe, Cu or Zn and supplemented with their corresponding solid minerals) to better study the effects of Trichoderma inoculation on plant growth and nutrition. Inoculated seedlings grown in Cu-deficient hydroponic conditions exhibited increases in dry plant biomass (92%) and Cu uptake (42%) relative to control plants. However, we did not observe a significant effect on seedling biomass in plants grown in the Fe- and Zn-deficient hydroponic conditions; by contrast, the biomass decreased by 82% in the P-deficient hydroponic condition. Thus, we demonstrated that Trichoderma SQR-T037 competed for P (phytate) and Zn with tomato seedlings by suppressing root development, releasing phytase and/or chelating minerals. The results of this study suggest that the induction of increased or suppressed plant growth occurs through the direct effect of T. harzianum on root development, in combination with indirect mechanisms, such as mineral solubilisation (including solubilisation via acidification, redox, chelation and hydrolysis).     

Assessment of lead availability in soils contaminated by mine spoil

The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration.Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap     

Effects of phosphate and pH stress on the growth and function of apple roots

Summary Effects of phosphate and pH stress on the growth and uptake functions of apple roots were studied over a period of fourteen days using split-root (2-way) seedlings in solution culture. The level of P fed to either or both halves of the root system was varied and a demineralized water control was also included. pH treatments consisted of using acidic nutrient solutions (pH 3 to 4) or nutrient solutions adjusted to pH 5.0 before use.Solution pH proved of paramount importance for the expression of P deficiency effects on root growth and water uptake. Where initial solution pH was favourable for root growth (pH 5), P deficiency stimulated root growth and water uptake per seedling even if the stress was localized. On the other hand, acidic solutions and the water control inhibited root growth and water uptake compared with +P controls. Where solution pH was favourable, P stress also led to an increase in the mean length per root versus the +P control suggesting that the plant adapted to stress by developing an exploratory type of root.Water use per seedling was predominantly a function of root size rather than leaf area since the treatments influenced root size to a much greater extent than leaf area. Uptake was positively related to root size in that adjusted solutions gave a higher water use than nonadjusted solutions. However, efficiency of water use per unit weight of root was consistently higher in the nonadjusted solutions and this appeared to be due to the presence of a larger number of root tips per unit weight of root in such solutions compared with root systems in pH adjusted solutions.Uptake of P per half root was higher from pH adjusted than from nonadjusted solutions and was also increased by increasing the P concentration. Further, for any one treatment P uptake per half root increased throughout the experiment indicating that uptake was influenced by root growth. However, in contrast to water uptake, uptake of P per unit weight or per unit surface area of root was not changed by pH adjustment nor was this parameter of uptake concentration dependent. That is, the above-mentioned pH and concentration effects on P uptake were mediated through effects on root growth.Comparing localized versus uniform placement of P, uptake of P was significantly higher from the uniform application. However, uptake from localized placement at pH 5 was markedly higher than uptake under pH stress and therefore if the pH of the medium remains favourable for root growth then the lower value for localized placement could probably be compensated for by further increasing the concentration of P applied.     

Uptake of Radioactivity by Aquatic Plants and Location in the Cells I. THE EFFECT OF pH ON THE STRONTIUM-90 AND YTTRIUM-90 UPTAKE BY THE GREEN ALGA ULVA LACTUCA AND THE EFFECT OF STABLE YTTRIUM ON YTTRIUM-90 UPTAKE

The uptake of strontium-90 and yttrium-90 by Ulva lactuca fromsea water was measured over a period of 179 days. In sea waterat normal pH (8.0) and without added carrier Ulva reached astrontium-90 equilibrium at 0.32 times the concentration inthe water within 3 hrs, but rapidly depleted the water of yttrium-90.Addition of 0.15 ppm of non-radioactive (stable) yttrium ledto the establishment of an yttrium-90 equilibrium within 3 hrs,with the Ulva having a concentration factor of 550. It was foundthat without added carrier the yttrium-90 remained on the outersurface of the plants, but when carrier was added the yttrium-90taken up mainly entered the cells and was laid down in the protoplasmicinclusions. The strontium-90 was located only in the protoplasmicinclusion. Uptake was investigated in a pH range 5.1 to 8.0.Progressive reductions of pH from 8.0 to 6.5 led to a smallincrease in the amount of strontium-90 uptake but to large increasein the yttrium-90 uptake. However, in the pH range 5.8 to 5.1the yttrium-90 uptake was greatly reduced. External pH below6.0 caused death of the alga within 5 days. The effect of pHon strontium uptake is thought to be due to changes in equilibriumin the carbonate-bicarbonate system. The effects of pH and stableyttrium concentration on yttrium-90 uptake are discussed interms of changes in the state of yttrium in the sea water, resultingin increased availability to the plant, and of changes in thenature of the plant surface resulting from its physiologicalresponse to lowered pH.     

Ion exchange/complexation of the uranyl ion by Rhizopus biosorbent

Nonliving biomass of nine Rhizopus species effectively sequestered the uranyl ion from solution, taking up 150-250 mg U/g dry cells at 300 ppm U equilibrium concentration in solution, and 100-160 mg U/g dry cells with 100 ppm U in solution. The affinity of this biosorbent for the uranyl ion was found to be affected by timing of harvesting and medium composition. Uptake of the uranyl ion by nonliving biomass of Rhizopus oligosporus was due to ion exchange or complexation, since binding was reversed by the addition of complexing ligands or the reduction of pH to a value less than 2. Uptake isotherms were interpreted in terms of a model of multiple equilibria. At pH 相似文献   

Nitrate Uptake by Manganese-Deficient Lemon Plants

The uptake of nitrate and water was followed in Eureka lemon (Citrus limon (L.) Burm. f.) plants grown in solution culture in a greenhouse under short (3–6 months) and long-term (22–24 months) Mn-nutrition stress. Uptake was determined from depletion in the nutrient solution. Under short-term stress, manganese-deficient plants absorbed 14.5% more nitrate and 3.4% more water than the control plants, on a weight basis. Under long-term stress there was a three-fold increase in nitrate and a two-fold increase in water uptake in the Mn-deficient plants. The intensive nitrate uptake under Mn-deficiency stress was more spectacularly demonstrated in plants which were exposed also to low nitrogen supply. The low-nitrogen Mn-deficient plants absorbed more nitrate, had less stunted growth and developed fewer visible symptoms of both N and Mn deficiencies than high-nitrogen Mn-deficient plants.     

Cadmium triggers Elodea canadensis to change the surrounding water pH and thereby Cd uptake

This study was aimed to investigate the influence of Elodea canadensis shoots on surrounding water pH in the presence of cadmium and the effect of plant-induced pH on cadmium uptake. The pH change in the surrounding nutrient solution and Cd uptake by Elodea shoots were investigated after cultivation of various plant densities (1, 3, 6 plants per 500 ml) in hydroponics at a starting pH of 4.0 and in the presence of different concentrations of cadmium (0, 0.1, 0.5 microM). Cadmium uptake was also investigated at different constant pH (4.0, 4.5, 5.5 and 6.5). To investigate if the pH change arose from photosynthetic activities, plants were grown under light, darkness or in the presence of a photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and 0.5 microM cadmium in the solution. Elodea had an ability to increase the surrounding water pH, when the initial pH was low, which resulted in increased accumulation of Cd. The higher the plant density, the more pronounced was the pH change. The pH increase was not due to the photosynthetic activity since the pH rise was more pronounced under darkness and in the presence of DCMU. The pH increase by Elodea was triggered by cadmium.     

The sweet side of misbalanced nutrients in cadmium-stressed plants

Some plants are able to maintain or improve their performance under cadmium (Cd) exposure, despite high Cd concentrations in roots and shoots, indicating that they have protective strategies to neutralise the side effects from Cd accumulation. The regulation of antioxidant machinery and the mitigation of Cd uptake and translocation have been the focus of several studies, but evidence shows that the modulation of nutritional status is also involved in tolerance mechanisms. Although alterations in the nutrient concentrations are usually coupled to negative outcomes on the development of plants under Cd exposure, current works have shown their “sweet” sides. Here, we provide evidence that the degree of plant tolerance to short Cd exposure is, at least partially, associated with differential changes in magnesium (Mg), manganese (Mn) and boron (B) status, all of which modulate physiological and developmental events, such as root architecture (Mg and/or B status), ionomic balance (Mn and/or B status), biomass production (Mg and/or Mn status) and biomass allocation (Mg/K ratio). Modulation of root architecture can be a strategy to obtain water and nutrients in metal-free patches in a growing medium. Changes in the uptake and/or distribution of nutrients may adjust the ionomic profile to equilibrate charge and pH homeostasis after Cd entrance into the plant. Alterations in the Mn and Mg status may alter the balance between photorespiratory and photosynthetic metabolisms. Finally, reprogramming biomass allocation among organs can be a strategy to remodelling plant body in order to better cope with environmental challenges. The identification and understanding of plant tolerance mechanisms against heavy metal toxicity is necessary to support strategies to mitigate their impacts on crop productivity and quality, supporting food security in increasing environmental contamination in the Anthropocene.