Nickel Hyperaccumulator Research Articles

The metal transporter PgIREG1 from the hyperaccumulator Psychotria gabriellae is a candidate gene for nickel tolerance and accumulation

Nickel is an economically important metal and phytotechnologies are being developed to limit the impact of nickel mining on the environment. More than 300 plant species are known to hyperaccumulate nickel. However, our knowledge of the mechanisms involved in nickel accumulation in plants is very limited because it has not yet been possible to study these hyperaccumulators at the genomic level. Here, we used next-generation sequencing technologies to sequence the transcriptome of the nickel hyperaccumulator Psychotria gabriellae of the Rubiaceae family, and used yeast and Arabidopsis as heterologous systems to study the activity of identified metal transporters. We characterized the activity of three metal transporters from the NRAMP and IREG/FPN families. In particular, we showed that PgIREG1 is able to confer nickel tolerance when expressed in yeast and in transgenic plants, where it localizes in the tonoplast. In addition, PgIREG1 shows higher expression in P. gabriellae than in the related non-accumulator species Psychotria semperflorens. Our results designate PgIREG1 as a candidate gene for nickel tolerance and hyperaccumulation in P. gabriellae. These results also show how next-generation sequencing technologies can be used to access the transcriptome of non-model nickel hyperaccumulators to identify the underlying molecular mechanisms.

Nickel Accumulation by Streptanthus polygaloides (Brassicaceae) Reduces Floral Visitation Rate

Hyperaccumulation is the phenomenon whereby plants take up and sequester in high concentrations elements that generally are excluded from above-ground tissues. It largely is unknown whether the metals taken up by these plants are transferred to floral rewards (i.e., nectar and pollen) and, if so, whether floral visitation is affected. We grew Streptanthus polygaloides, a nickel (Ni) hyperaccumulator, in short-term Ni supplemented soils and control soils to determine whether Ni is accumulated in floral rewards and whether floral visitation is affected by growth in Ni-rich soils. We found that while supplementation of soils with Ni did not alter floral morphology or reward quantity (i.e., anther size or nectar volume), Ni did accumulate in the nectar and pollen-filled anthers-providing the first demonstration that Ni is accumulated in pollinator rewards. Further, S. polygaloides grown in Ni-supplemented soils received fewer visits per flower per hour from both bees and flies (both naïve to Ni-rich floral resources in the study area) relative to plants grown in control soils, although the probability a plant was visited initially was unaffected by Ni treatment. Our findings show that while Ni-rich floral rewards decrease floral visitation, floral visitors are not completely deterred, so some floral visitors may collect and ingest potentially toxic resources from metal-hyperaccumulating plants. In addition to broadening our understanding of the effects of metal accumulation on ecological interactions in natural populations, these results have implications for the use of insect-pollinated plants in phytoremediation.

English

Sánchez-Mata, D., de la Fuente, V., Rufo, L., Rodríguez, N. & Amils, R. Streptanthus purpureus sp. nova (Cruciferae), an endemic nickel hyperaccumulator from Sierra Nevada (California, USA). Lazaroa 34: (2013).The genus Streptanthus Nutt. (Cruciferae) is one of the most important indicators of ultramafic floras in Western North America. This genus contains taxa that are endemic or tolerant of ultramafic soils. One of these taxa, Streptanthus polygaloides sensu lato (s.l.) are annual nickel hyperaccumulators strictly confined to ultramafic soils throughout the Californian Sierra Nevada foothills. Some clarifications are discussed regarding the taxonomy and ecology of this complex, leading to the recognition of a new taxon: Streptanthus purpureus sp. nova

Localization of Nickel in Tissues of Streptanthus polygaloides Gray (Cruciferae) and Endemic Nickel Hyperaccumulators from California

The genus Streptanthus Nutt. is one of the most important indicators of ultramafic floras in western North America. This genus contains taxa that are endemic or tolerant of ultramafic soils. Streptanthus polygaloides is an annual nickel hyperaccumulator strictly confined to ultramafic soils throughout the Californian Sierra Nevada foothills. Nickel concentration in S. polygaloides populations was evaluated by elemental microanalysis using inductively coupled plasma mass spectrometry (ICP-MS). Representative samples of S. polygaloides roots, stems, leaves, flowers, and fruits were studied by scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray probe (SEM-EDX). Results show Ni accumulation values between 0.09 and 1.18%, and a distribution pattern similar to that observed in other Ni hyperaccumulator taxa, with the leaf epidermis accumulating the largest concentrations.

The potential use of indigenous nickel hyperaccumulators for small-scale mining in The Philippines

Uptake of nickel and three other heavy metals (copper, cobalt, and chromium) was examined in 33 species of the common and rare native vascular plants growing in an ultramafic area currently subjected to mining in Zambales Province, Luzon, Philippines. Leaf tissue samples were initially screened in the field using filter paper impregnated with dimethylglyoxime (1% solution in 70% ethyl alcohol) and later analyzed by atomic absorption spectroscopy. One species was found to be a hypernickelophore (>10,000 µg/g), eight species were nickel hyperaccumulators (>1,000 µg/g), nineteen species were hemi-accumulators (>100-1,000 µg/g), and five species were non-accumulators (<100 µg/g). This paper significantly adds to the list of hyperaccumulator species first reported for the Philippines in 1992. The findings will be discussed in context of using indigenous species for post mining ecological restoration and nickel phytoextraction in small-scale mining in the Philippines

The role of elevation and soil chemistry in the distribution and ion accumulation of floral morphs of Streptanthus polygaloides Gray (Brassicaceae), a Californian nickel hyperaccumulator

Background: The flora of serpentine/ultramafic soils provides an excellent model system for the study of natural selection in plant populations. Streptanthus polygaloides is a nickel hyperaccumulator that is endemic to serpentine soils in the Sierra Nevada of California, and has four floral morphs (yellow, purple, yellow-to-purple and undulate).Aims: We investigate three hypotheses: (1) the purple morph occurs in colder, wetter climates than the yellow morph; (2) tissue–soil ionic relationships differ among morphs; and (3) morphs occur on soils with differing elemental concentrations.Methods: We queried herbarium records to investigate patterns of occurrence among the yellow and purple floral morphs, and analysed soil and tissue samples from wild populations of all four morphs.Results: The purple morph inhabited serpentine outcrops with colder temperatures and greater precipitation levels than the yellow morph. Concentrations of elements in leaf tissue and rhizosphere soil differed little among populations of the morphs, but showed substantial within-site variation.Conclusions: Our results suggest that a climatic gradient may be responsible for divergence in floral colour among populations of S. polygaloides. Because of the large within-site variation in soil and tissue elemental concentrations, plants appear to have a varied physiological response to edaphic factors, regardless of morph membership.

Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale

Mitochondria are important targets of metal toxicity and are also vital for maintaining metal homeostasis. Here, we examined the potential role of mitochondria in homeostasis of nickel in the roots of nickel hyperaccumulator plant Alyssum murale. We evaluated the biochemical basis of nickel tolerance by comparing the role of mitochondria in closely related nickel hyperaccumulator A. murale and non-accumulator Alyssum montanum. Evidence is presented for the rapid and transient influx of nickel in root mitochondria of nickel hyperaccumulator A. murale. In an early response to nickel treatment, substantial nickel influx was observed in mitochondria prior to sequestration in vacuoles in the roots of hyperaccumulator A. murale compared with non-accumulator A. montanum. In addition, the mitochondrial Krebs cycle was modulated to increase synthesis of malic acid and citric acid involvement in nickel hyperaccumulation. Furthermore, malic acid, which is reported to form a complex with nickel in hyperaccumulators, was also found to reduce the reactive oxygen species generation induced by nickel. We propose that the interaction of nickel with mitochondria is imperative in the early steps of nickel uptake in nickel hyperaccumulator plants. Initial uptake of nickel in roots results in biochemical responses in the root mitochondria indicating its vital role in homeostasis of nickel ions in hyperaccumulation.

Ultramafic nickel laterites in Indonesia (Sulawesi, Halmahera): Mining, nickel hyperaccumulators and opportunities for phytomining

Indonesia (Sulawesi and Halmahera Islands) has some of the largest surface exposures of ultramafic bedrock in the world, and these are the sites of productive lateritic nickel mining operations. The proven and potential use of native plant species of ultramafic outcrops in mine rehabilitation can help drive conservation efforts, and nickel hyperaccumulators in particular can potentially be used in phytomining. The phytomining operation uses hyperaccumulators to extract residual nickel from stripped land. As such, in the foreseeable future, implementation of this technology is likely to be seen as a part of a progressive rehabilitation strategy of lateritic nickel mining in Indonesia. This approach ensures effective erosion control (e.g. ‘re-greening’) while at the same time generating income by gaining residual nickel.

Localization and distribution of nickel and other elements in in-vitro grown Alyssum corsicum exhibiting morphological changes in trichomes: initial insights into molecular mechanisms of nickel hyperaccumulation

Alyssum corsicum Duby is a candidate plant used for phytomining and phytoremediation studies with its high Ni-accumulating ability of the aboveground tissues. Metal localization and concentration by hyperaccumulator plants and the physiological basis of these phenomena have been of great interest in recent years. A. corsicum seeds were grown at different concentrations of Ni in Murashige and Skoog medium. Multielement concentrations of the plant roots and shoots were determined by polarized energy dispersive X-ray fluorescence. Ni, Ca, Mg, and Fe localization and concentration at the upper and lower leaf surfaces were determined by scanning electron microscopy coupled with the energy-dispersive X-ray analysis technique (SEM-EDX). Results showed that Ni is accumulated more by the shoots than the roots of the plant and that Ni is concentrated mainly in the trichome and the stoma guard cells of the leaves. Trichome density on the leaves was reduced, and some morphological changes of the trichome structure were also observed with increasing Ni levels. Analysis of antioxidant enzyme activities in roots and shoots was performed. The total leaf proteins of the plant were examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, and differentially expressed genes were detected by specifically designed primers.

Symbiotic interactions of culturable microbes with the nickel hyperaccumulator Berkheya coddii and the herbivorous insect Chrysolina clathrata

Chrysolina clathrata is a specialized phytophagous beetle feeding exclusively on the herbaceous nickel hyperaccumulating plant Berkheya coddii. These organisms appear impervious to the toxic levels of nickel in their environment. In the current study we aimed to identify microorganisms that may have symbiotic relationships with these organisms. Culture techniques were used to isolate bacteria and fungi from plants and the faeces of beetles reared under laboratory conditions. The identity of isolates was determined using morphology and molecular techniques. Several genera of filamentous fungi (Alternaria, Aspergillus, Bipolaris, Cladosporium, Epicoccum, Fusarium, and Penicillium), yeasts (Cryptococcus, Meyerozyma, and Rhodotorula), as well as endophytic bacteria (Bacillus and Lysinibacillus) were isolated from the leaves of the plant. We also selectively isolated yeasts (Candida, Cryptococcus, Debaryomyces, Meyerozyma and Wickerhamomyces) from the beetle’s faeces. Subsequently we determined the minimum inhibitory Ni-concentration (MIC) of all isolates. The endophytic bacteria, filamentous fungi and the yeasts Candida intermedia, Cryptococcus flavescens and Meyerozyma guilliermondii, showed notable Ni resistance, while the beetle’s gut seems to select for Ni resistant yeasts.

Elemental and metabolite profiling of nickel hyperaccumulators from New Caledonia

Leaf material from nine Ni hyperaccumulating species was collected in New Caledonia: Homalium kanaliense (Vieill.) Briq., Casearia silvana Schltr, Geissois hirsuta Brongn. & Gris, Hybanthus austrocaledonicus Seem, Psychotria douarrei (G. Beauvis.) Däniker, Pycnandra acuminata (Pierre ex Baill.) Swenson & Munzinger (syn Sebertia acuminata Pierre ex Baill.), Geissois pruinosa Brongn. & Gris, Homalium deplanchei (Viell) Warb. and Geissois bradfordii (H.C. Hopkins). The elemental concentration was determined by inductively-coupled plasma optical emission spectrometry (ICP-OES) and from these results it was found that the species contained Ni concentrations from to 250-28,000 mg/kg dry mass. Gas chromatography mass spectrometry (GC-MS)-based metabolite profiling was then used to analyse leaves of each species. The aim of this study was to target Ni-binding ligands through correlation analysis of the metabolite levels and leaf Ni concentration. Approximately 258 compounds were detected in each sample. As has been observed before, a correlation was found between the citric acid and Ni concentrations in the leaves for all species collected. However, the strongest Ni accumulator, P. douarrei, has been found to contain particularly high concentrations of malonic acid, suggesting an additional storage mechanism for Ni. A size exclusion chromatography separation protocol for the separation of Ni-complexes in P. acuminata sap was also applied to aqueous leaf extracts of each species. A number of metabolites were identified in complexes with Ni including Ni-malonate from P. douarrei. Furthermore, the levels for some metabolites were found to correlate with the leaf Ni concentration. These data show that Ni ions can be bound by a range of small molecules in Ni hyperaccumulation in plants.

Effects of Nickel Hyperaccumulation on Physiological Characteristics of Alyssum Murale Grown on Metal Contaminated Waste Amended Soil

A pot experiment was conducted to investigate the effect of nickel concentration on physiological characteristics of Alyssum murale when grown in a soil mixed with sewage sludge (at the rate of 2.8%). Two types of sludge were used: agricultural sewage sludge (S1) and industrial sewage sludge with an increasing nickel concentration (S2, S3, and S4). Results showed that Ni in shoots was higher than Ni in roots. A. murale is able to concentrate up to 12730 mg/kg Ni in leaves. The highest dry matter yield was observed with plants grown with agricultural sewage sludge. An addition of S2 and S3 increased shoot biomass. However, application of S4 reduced 40% shoot dry weight as compared to the control. Ni treatment did not affect all chlorophyll fluorescence parameters. The Fv/Fm ratio was stable between Ni treatments. Photosynthesis rate (A) increased with agricultural sewage sludge, but remained stable with variable Ni rates from the industrial sludge. The chlorophyll content increased with S1, S2 and S3 but it remains constant with S4 when compared to the control. Therefore, high nickel concentration did not affect the function of the photosynthetic machine of A. murale.

The chemical exploitation of nickel phytoextraction: An environmental, ecologic and economic opportunity for New Caledonia

Herein, we explore the outlines of an innovative method based on the chemical recovery of metal-rich biomass produced in phytoextraction technologies. Taking advantage of the adaptive capacity of some New Caledonian plants to hyperaccumulate Ni2+ cations in their aerial parts, this technique is based on the direct use of metals derived from plants as “Lewis acid” catalysts in organic chemistry. Metallic cations contained in New Caledonian nickel hyperaccumulators are recovered through a simple cost-effective process and serve the preparation of heterogeneous catalysts used in synthetic transformations allowing access to molecules with high added-value. The design of all processes is in line with the principles of green chemistry; it is adapted to the new economic constraints; it offers a new relevant outlet for metal-rich biomass; and it represents an alternative to non-renewable mineral materials.

Antioxidative-related enzyme activity in Alyssum markgrafii shoot cultures as affected by nickel level

Shoot cultures of rare Balkan hyperaccumulating species Alyssum markgrafii were subjected to high nickel concentrations of 1, 3, 5, and 8 mM. The effects of graded nickel concentrations on toxicity, pigments, and several components of plant antioxidative defense system were characterized. Toxic effects of excess nickel were observed through slower growth and biomass decrease, together with increased reactive oxygen species (ROS) production and lipid peroxidation. Nickel exposure decreased chlorophyll a, b, total chlorophyll as well as carotenoid concentration. Addition of sodium benzoate, potent ROS scavenger, showed concentration-dependent disturbing effect on nickel hyperaccumulation, lowering the content of accumulated nickel in A. markgrafii shoots. General reducing power represented by low molecular weight antioxidants and phenols was inversely correlated with nickel concentration. Among the investigated antioxidative enzymes, POD seems to play important role in ROS level regulation upon excessive nickel in medium.

Hyperaccumulation of nickel by Alyssum corsicum is related to solubility of Ni mineral species

Aims Past studies have demonstrated that hyperaccumulators absorb Ni from the same labile pools in soil as normal plant species. This study investigated whether the Ni hyperaccumulator plant Alyssum corsicum possesses distinct extraction mechanisms for different Ni species present in soils. Different Ni species have different solubilities and potential bioavailabilities to roots.

Bioaccumulation of Cr, Hg, As, Pb, Cu and Ni with the ability for hyperaccumulation by Amaranthus dubius

Amaranthus dubius is a nutritious leafy vegetable that is widely distributed in Africa, Asia and South America. The rapid growth and biomass makes them one of the highest yielding leafy crops, which may be valuable for phytoremediation. Thus, this study investigates the potential of A. dubius for the hyperaccumulation and distribution of chromium (Cr), mercury (Hg), arsenic (As), lead (Pb), copper (Cu) and nickel (Ni) in the different plant organs. The phytoremediation was calculated by the bioconcentration factor and translocation factor of plants grown under controlled conditions in a tunnel house. The metal accumulated was investigated using inductively coupled plasma mass spectroscopy (ICPMS). Following exposure to 25, 75 and 100 ppm of Cr, Hg, As, Pb, Cu and Ni respectively for four days, A. dubius accumulates Cr, Hg and Pb at the low concentration (25 ppm) and translocates it to the shoots, but at higher concentrations (75 and 100 ppm) the metal is only stored in the roots. In the case of As accumulation at all concentrations, the metal is translocated to the shoots; Cu and Ni indicate that the metal is stored in the roots mainly. This study indicates that A. dubius has limited potential for the bioaccumulation of Cr, Hg, Pb, Cu and Ni, but is capable of hyperaccumulating of As. Key words: Amaranthus dubius, bioconcentration factor, translocation factor, inductively coupled plasma mass spectroscopy.

Nickel hyperaccumulation by natural plants in Turkish serpentine soils

Natural plants in Turkish serpentine soils were surveyed to determine their Ni accumulation capability. Geographic distribution and diethylene triamine pentaacetic acid (DTPA)-extractable nickel contents of the western Anatolian serpentine soils and their vegetative contents were studied to find the possible relationships between the phytoavailable Ni amount in the soil and the Ni content of potential accumulator plants. Over half of the surface area of Turkey was targeted in the study. Aboveground parts of 413 herbaceous plants and the surface soil (0-15 cm) of 192 serpentine samples were collected. A digital elevation model and ANUSPLIN and ArcGIS 8.1 software packages were employed for generation of climatic surfaces and analysis in preparation of comparative maps. Scientifically approved Ni hyperaccumulator plant taxa as well as readily emerging species were tested under greenhouse and climate chamber conditions. The varying magnitude of nickel determined in the aboveground parts of the test plants indicated that the resistance or vulnerability and Ni requirements of a plant species were species-specific and were more effective than the Ni amount in the soil on the uptake of the element. Significant differences were found between the amount of DTPA-extractable Ni in the soil and the Ni content of hyperaccumulator Brassicaceae plants grown in the same soil bodies. Isatis pinnatiloba, which is endemic to Turkey, was introduced as a nickel hyperaccumulator species. Bottlenecks and drawbacks of phytoremediation techniques for commercial use were discussed.

Differential Regulation of Serine Acetyltransferase Is Involved in Nickel Hyperaccumulation in Thlaspi goesingense

When growing in its native habitat, Thlaspi goesingense can hyperaccumulate 1.2% of its shoot dry weight as nickel. We reported previously that both constitutively elevated activity of serine acetyltransferase (SAT) and concentration of glutathione (GSH) are involved in the ability of T. goesingense to tolerate nickel. A feature of SAT is its feedback inhibition by l-cysteine. To understand the role of this regulation of SAT by Cys on GSH-mediated nickel tolerance in T. goesingense, we characterized the enzymatic properties of SATs from T. goesingense. We demonstrate that all three isoforms of SAT in T. goesingense are insensitive to inhibition by Cys. Further, two amino acids (proline and alanine) in the C-terminal region of the cytosolic SAT (SAT-c) from T. goesingense are responsible for converting the enzyme from a Cys-sensitive to a Cys-insensitive form. Furthermore, the Cys-insensitive isoform of SAT-c confers elevated resistance to nickel when expressed in Escherichia coli and Arabidopsis thaliana, supporting a role for altered regulation of SAT by Cys in nickel tolerance in T. goesingense.

Cadmium phytoextraction potential of different Alyssum species

This work was planned for providing useful information about the possibility of using serpentine adapted plants for phytoextraction of cadmium, element scarcely represented in such metalliferous environment. To this aim, we investigated variation in cadmium tolerance, accumulation and translocation in three Alyssum plants with different phenotypes: Alyssum bertolonii, that is a serpentine endemic nickel hyperaccumulator, and two populations of Alyssum montanum, one adapted and one not adapted to serpentine soils. Plants were hydroponically cultivated in presence of increasing concentrations of CdSO 4 for two weeks. For the metal concentration used in the experiments, the three different Alyssum populations showed variation in cadmium tolerance, accumulation and content. The serpentine adapted population of A. montanum showed statistically higher cadmium tolerance and accumulation than A. bertolonii and the population of A. montanum not adapted to serpentine soil thus deserving to be investigated for phytoextraction purposes. Furthermore, as for the kinetic parameters of the cadmium uptake system, A. montanum serpentine population presented a low apparent K m value, suggesting a high affinity for this metal of its uptake system, whereas the V max values were not significantly different among the plants. Present data revealed metallicolous plants are also suitable for the phytoremediation of metals underrepresented in the environment of their initial origin. Nonetheless, field trials on real contaminated soils are essential.

Influence of Drought Stress on the Nickel-Hyperaccumulating ShrubHybanthus floribundus(Lindl.) F.Muell. subsp.floribundus

Hyperaccumulation of nickel (Ni) in certain plants may play a role in drought resistance under water stress. This article tests the influence of water stress on the Ni-hyperaccumulating shrub Hybanthus floribundus Lindl. F.Muell. subsp. floribundus. Plants grown in 1000 mg kg−1 Ni-amended Clastic Rudosol were exposed to five levels of soil water potentials (−33 [field capacity], −60, −400, −600, and −1000 kPa) for 12 wk. Water stress did not induce significant changes in growth rate, relative water content, rates of gas exchange, or carbon isotope discrimination. Water use efficiency (WUE) values were approximately threefold lower in plants at water potentials <−400 kPa than they were in those at water potentials of −33 kPa. Low WUE values suggest that this species possesses an efficient water conservation mechanism that enables its survival in competitive water-limited environments. A 38% decline in water potential and a 68% decline in osmotic potential occurred between −1000- and −33-kPa water potential...