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Phytoremediation describes the treatment of environmental problems (bioremediation) through the use of plants. See also Nature The natural environment, commonly referred to simply as the environment, is a terminology that is comprised of all living and Bioremediation can be defined as any process that uses Microorganisms Fungi, green plants or their Enzymes to return the natural environment altered Plants are living Organisms belonging to the kingdom Plantae.

The word's etymology comes from the Greek φυτο (phyto) = plant, and Latin « remedium » = restoring balance, or remediating. Phytoremediation consists in depolluting contaminated soils, water or air with plants able to contain, degrade or eliminate metals, pesticides, solvents, explosives, crude oil and its derivatives, and various other contaminants, from the mediums that contain them. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Water is a common Chemical substance that is essential for the survival of all known forms of Life. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across A pesticide is a substance or mixture of substances used to kill a pest. A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied Petroleum ( L petroleum, from Greek πετρέλαιον, lit

It is clean, efficient, inexpensive and non-environmentally disruptive, as opposed to processes that require excavation of soil. The definitive textbook on phytoremediation was published in 2003 with contributed, peer reviewed articles from all major research groups involved in phytoremediation research (Phytoremediation: Transformation and Control of Contaminants, edited by Steven C. McCutcheon and Jerald L. Schnoor).

Contents

Various phytoremediation processes

A range of processes mediated by plants are useful in treating environmental problems:

Phytoextraction

Phytoextraction (or phytoaccumulation) uses plants to remove contaminants from soils, sediments or water into harvestable plant biomass. Phytoextraction has been growing rapidly in popularity world-wide for the last twenty years or so. Generally this process has been tried more often for extracting heavy metals than for organics. At the time of disposal contaminants are typically concentrated in the much smaller volume of the plant matter than in the initially contaminated soil or sediment. 'Mining with plants', or phytomining, is also being experimented with.

The plants absorb contaminants through the root system and store them in the root biomass and/or transport them up into the stems and/or leaves. A living plant may continue to absorb contaminants until it is harvested. After harvest a lower level of the contaminant will remain in the soil, so the growth/harvest cycle must usually be repeated through several crops to achieve a significant cleanup. After the process, the cleaned soil can support other vegetation.

Two versions of phytoextraction:

Examples of phytoextraction from soils (see also 'Table of hyperaccumulators'):

Phytostabilization

Phytostabilization focuses on long-term stabilization and containment of the pollutant. For example, the plant's presence can reduce wind erosion, or the plant's roots can prevent water erosion, immobilize the pollutants by adsorption or accumulation, and provide a zone around the roots where the pollutant can precipitate and stabilize. Unlike phytoextraction, phytostabilization mainly focuses on sequestering pollutants in soil near the roots but not in plant tissues. Pollutants become less bioavailable and livestock, wildlife, and human exposure is reduced. An example application of this sort is using a vegetative cap to stabilize and contain mine tailings. Tailings (also known as slimes, gangue, tailings pile, tails, leach residue, or slickens) are the materials left over [2]

Phytotransformation

In the case of organic pollutants, such as pesticides, explosives, solvents, industrial chemicals, and other xenobiotic substances, certain plants, such as Cannas, render these substances non-toxic by their metabolism. An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. A pesticide is a substance or mixture of substances used to kill a pest. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. A xenobiotic is a Chemical which is found in an Organism but which is not normally produced or expected to be present in it Canna (or Canna lily, although not a true Lily) is a Genus of approximately twenty Species of Flowering plants Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. In other cases, microorganisms living in association with plant roots may metabolize these substances in soil or water. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel These complex and recalcitrant compounds cannot be broken down to basic molecules (water, carbondioxide etc) by plant molecules, and hence the term phytotransformation represents a change in chemical structure without complete breakdown of the compound. The term "Green Liver Model" [5] is used to describe phytotransformation, as plants behave similar to the human liver when dealing with these xenobiotic compounds(foreign compound/pollutant). A xenobiotic is a Chemical which is found in an Organism but which is not normally produced or expected to be present in it After uptake of the xenobiotics, plant enzymes increase the polarity of the xenobiotics by adding functional groups such as hydroxyl groups (-OH). This is known as Phase I metabolism, similar to the way the human liver increases the polarity of drugs and foreign compounds (Drug Metabolism. While in the human liver, enzymes like Cytochrome P450s are responsible for the initial reactions, in plants enzymes such as nitroreductases carry out the same role. In the second stage of phytotransformation, known as Phase II metabolism, plant biomolecules such as glucose and amino acids are added to the polarized xenobiotic to further increase the polarity (known as conjugation). This is again similar to the processes occurring in the human liver wherein glucuronidation (addition of glucose molecules by the UGT (e. g. UGT1A1) class of enzymes) and glutathione addition reactions occur on reactive centers of the xenobiotic. Lack of expression of UGT1A1 in the neonatal liver is the Phase I and II reactions serve to increase the polarity and reduce the toxicity of the compounds, although many exceptions to the rule are seen at least in the case of the human liver. The increased polarity also allows for easy transport of the xenobiotic along aqueous channels. In the final stage of phytotransformation (Phase III metabolism), a sequestration of the xenobiotic occurs within the plant. The term sequestration can have different meanings according to the context The xenobiotics polymerize in a lignin-like manner and get a complex structure which is sequestered in the plant. Lignin or lignen is a complex Chemical compound most commonly derived from Wood and an integral part of the secondary Cell walls of Plants This ensures that the xenobiotic is safely stored in the plant, and does not affect the functioning of the plant. However, preliminary studies have shown that these plants can be toxic to small animals (such as snails) and hence plants involved in phytotransformation may need to be maintained in a closed enclosure. The human liver differs from plants in Phase III metabolism, since the liver can transport the xenobiotics into the bile for eventual excretion. Since plants have no excretory mechanisms, they sequester the modified xenobiotics. Hence, the plants reduce toxicity (with exceptions) and sequester the xenobiotics in phytotransformation. Trinitrotoluene phytotransformation has been extensively researched a transformation pathway has been proposed [3]. Trinitrotoluene ( TNT) is a Chemical compound with the formula C6H2(NO23CH3

The role of genetics

Breeding programs and genetic engineering are powerful methods for enhancing natural phytoremediation capabilities, or for introducing new capabilities into plants. Genetic engineering, Recombinant DNA technology, genetic modification/manipulation (GM and gene splicing are terms that apply to the direct Genes for phytoremediation may originate from a micro-organism or may be transferred from one plant to another variety better adapted to the environmental conditions at the cleanup site. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually For example, genes encoding a nitroreductase from a bacterium were inserted into tobacco and showed faster removal of TNT and enhanced resistance to the toxic effects of TNT [4].

Advantages and limitations

Hyperaccumulators and biotic interactions

This section is for the first four points (Protection, Interferences, Mutualism, and Commensalism) mainly inspired from the article: The significance of metal hyperaccumulation for biotic interactions, by R. S. Boyd and S. N. Martens[5].

A plant is said to be a hyperaccumulator if it can concentrate the pollutants in a minimum percentage which varies according to the pollutant involved (for example: more than 1000 mg/kg of dry weight for nickel, copper, cobalt, chromium or lead; or more than 10,000 mg/kg for zinc or manganese. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Manganese (ˈmæŋgəniːz is a Chemical element, designated by the symbol Mn. [6] Most of the 215 metal-hyperaccumulating species included in their review hyperaccumulate nickel. They listed 145 hyperaccumulators of nickel (around 300 Ni accumulators are known; see Hyperaccumulators table – 2 : Nickel and its notes), 26 of cobalt, 24 of copper, 14 of zinc, four of Lead, and two of Chromium. This section covers known Nickel hyperaccumulators accumulators or species tolerant to nickel This capacity for accumulation is due to hypertolerance, or phytotolerance: the result of adaptative evolution from the plants to hostile environments along multiple generations. Boyd and Martens list 4 biotic interactions that may be affected by metal hyperaccumulation, to which can be added the biofilm as a particular aspect of micorrhizae:

  1. protection
  2. Interferences with neighbour plants of different species
  3. Mutualism (Mycorrhizal associations or micorrhizae, and Pollen and seed dispersal)
  4. Commensalism
  5. The biofilm

Protection

More and more evidence show that the metals in hyperaccumulating plants give them some protection from various bacteria, fungi and / or insects. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface For instance, with foliar Ni concentrations as low as 93 mg/kg, the larval weight of Spodoptera exigua (Lepidoptera: Noctuidae) (beet army worm) is reduced and time to pupation extended (Boyd & Moar, subm. ).

Information published supporting the defence hypothesis of metal hyperaccumulation
Paper Plant species Metal Organism(s) affected
Ernst 1987 Silene vulgaris (Moench) Garke Cu (400 mg g-¹) Hadena cucubalis Schiff. (Lepidoptera: Noctuidae)
Boyd et al. 1994 Streptanthus polygaloides Gray Ni Xanthomonas campestris (Gram-negative bacterium)
Boyd et al. 1994 Streptanthus polygaloides Gray Ni Alternaria brassicicola (Imperfect fungus)
Boyd et al. 1994 Streptanthus polygaloides Gray Ni Erisyphe polygoni (Powdery mildew)
Martens & Boyd 1994 Streptanthus polygaloides Ni Pieris rapae L. The Small White ( Pieris rapae) is a small to mid-sized butterfly Species of the Yellows-and-Whites family Pieridae. (Lepidoptera: Pieridae)
Boyd & Martens 1994 Thlaspi montanum L. Lepidoptera is an order of Insect that includes Moths and butterflies. The Pieridae are a large family of butterflies with about 76 genera containing approximately 1100 species mostly from tropical Africa and Asia var. montanum Ni Pieris rapae
Pollard & Baker 1997 Thlaspi caerulescens J. The Small White ( Pieris rapae) is a small to mid-sized butterfly Species of the Yellows-and-Whites family Pieridae. and C. Presl. Zn Schistocerca gregaria (Forsk. Plagues of the Desert Locust ( Schistocerca gregaria) have threatened agricultural production in Africa, the Middle East and Asia ) (Orthoptera: Acrididae)
Pollard & Baker 1997 Thlaspi caerulescens J. and C. Presl. Zn Deroceras carvanae (Pollonera) (Pulmonata: Limacidae)
Pollard & Baker 1997 Thlaspi caerulescens J. The Pulmonata or "pulmonates" are an order (once a Subclass) of Snails and Slugs that have developed a pallial Lung and C. Presl. Zn Pieris brassicae L. The Large White, also called Cabbage Butterfly or Cabbage White ( Pieris brassicae) is a Butterfly in the family Pieridae (Lepidoptera: Pieridae)

The defense against viruses is not always supported. Lepidoptera is an order of Insect that includes Moths and butterflies. The Pieridae are a large family of butterflies with about 76 genera containing approximately 1100 species mostly from tropical Africa and Asia Davis et al. (2001) have compared two close species S. polygaloides Gray (Ni hyperaccumulator) and S. insignis Jepson (non-accumulator), inoculating them with Turnip mosaic virus. They showed that the presence of nickel weakens the plant's response to the virus. [7]

Circumvention of plants' elemental defences by their predators may occur in three ways[5]: (1) selective feeding on low-metal tissues, (2) use of a varied diet to dilute metal-containing food (likely more efficient in large-sized herbivores), and (3) tolerance of high dietary metal content.

  1. - Avoidance of an elemental defence via selective feeding:

Mishra & Kar (1974)[8] reported nickel to be transported through the xylem of crop plants. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 In Vascular plants xylem is one of the two types of transport tissue Phloem being the other Similarly, Kramer et al. (1996) showed that Ni is transported as a complex with the amino-acid histidine in the xylem. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Histidine (abbreviated as His or H) is one of the 20 standard Amino acids present in Proteins In the Nutritional sense in In Vascular plants xylem is one of the two types of transport tissue Phloem being the other This implies that phloem fluid may contain little nickel; thus phloem fluid may be used by able organisms as a rich source of carbohydrates. In Vascular plants phloem is the living tissue that carries organic Nutrients (known as photosynthate particularly Sucrose, a sugar to Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 In Vascular plants phloem is the living tissue that carries organic Nutrients (known as photosynthate particularly Sucrose, a sugar to

Pea aphids (Acyrthosiphon pisum [Harris]; Homoptera: Aphididae) feeding on Streptanthus polygaloides Gray (Brassicaceae) have equal survival and reproduction rates for plants containing ca. 5000 mg/kg nickel amended with NiCl2, and those containing 40 mg/kg nickel. This means that either the phloem fluid is poor in nickel even for nickel hyperaccumulators, or that the aphids tolerate nickel. Moreover the aphids feeding on high nickel-content plants only show a small increase of nickel content in their bodies, relatively to the nickel content of aphids feeding on low-nickel plants[5]. On the other hand, aphids (Brachycaudus lychnidis L. ) fed on the zinc-tolerant plant Silene vulgaris (Moench) Garcke (Caryophyllaceae) - which can contain up to 1400 mg/kg zinc in its leaves – were reported showing elevated (9000 mg/kg) zinc in their bodies.

Hopkin (1989)[9] and Klerks (1990)[10] demonstrated it for animal species; Brown & Hall (1990)[11] for fungal species; and Schlegel & al. (1992) and Stoppel & Schlegel (1995) for bacterial species.

Plants of Streptanthus polygaloides (Brassicaceae, Ni hyperaccumulator) can be parasited by Cuscuta californica var. breviflora Engelm. (Cuscutaceae). Metal contents of Cuscuta ranged from 540–1220 mg/kg Ni, 73-fold higher than the metal contents of Cuscuta parasitizing a co-occurring non-hyperaccumulator plant species. Cuscuta plants are therefore very Ni-tolerant[5] - 10 mg Ni/kg is sufficient for growth to start decreasing in unadapted plants[12]. According to Boyd & Martens (subm. ) this is "the first well-documented instance of the transfer of elemental defences from a hyperaccumulating host to a seed plant parasite".

Interferences with neighbour plants of different species

Its likelihood between hyperaccumulators and neighbouring plants was suggested but no mechanism was proposed. [6] Gabrielli et al. (1991)[13], and Wilson & Agnew (1992)[14], suggested a decrease in competition experienced by the hyperaccumulators for the litterfall from hyperaccumulators' canopy.

This mechanism mimics allelopathy in its effects, although technically due to redistribution of an element in the soil rather than to the plant manufacturing an organic compound. Boyd et Martens call it ‘‘elemental allelopathy’’ - without the autoxicity problem met in other types of allelopathy (Newman 1978).

Mutualism

Two types of mutualism are considered here, mycorrhizal associations or mycorrhizae, and animal-mediated pollen or seed dispersal.

1 - Mycorrhizal associations or mycorrhizae

There are two types of mycorrhizal fungi: ectomycorrhizae and endomycorrhizae. Ectomycorrhizae form sheaths around plant roots, endomycorrhizae enter cortex cells in the roots[15].

Mycorrhizae are the symbiotic relationship between a soil-borne fungus and the roots of a plant. A mycorrhiza (Greek for fungus roots coined by Frank 1885 typically seen in the plural forms mycorrhizae or mycorrhizas) is a symbiotic (occasionally Some hyperaccumulators may form mycorrhizae and, in some cases, the latter may have a role in metal treatment. [5]. In soils with low metal levels, vesicular arbuscular mycorrhizae enhance metal uptake of non-hyperaccumulating species[11]. An arbuscular mycorrhiza (plural mycorrhizae or mycorrhizas) is a type of Mycorrhiza in which the Fungus penetrates the cortical cells of the On the other hand, some mycorrhizae increase metal tolerance by decreasing metal uptake in some low-accumulating species. Mycorrhizae thus assists Calluna in avoiding Cu and Zn toxicity[16]. Most roots need about 100 times the amount of carbon than do the hyphae of its associated ectomycorrhizae in order to develop across the same amount of soil[17]. It is therefore easier for hyphae to acquire elements that have a low mobility than it is for plant roots. Caesium-137 and strontium-90 both have low mobilities[18].

Mycorrhizal fungi depend on host plants for carbon, while enabling host plants to absorb the soil's nutrients and water with more efficiency[19]. In mycorrhizae, nutrient uptake is enhanced for the plants while they provide energy-rich organic compounds to the fungus[20]. Although certain plant species that are normally symbiotic with mycorrhizal fungi can exist without the fungal association, the fungus greatly enhances the plant’s growth. Hosting mycorrhizae is much more energy effective to the plant than producing plant roots[21].

The Brassicaceae family reportedly forms few mycorrhizal associations. Brassicaceae or Cruciferae, also known as the crucifers, the mustard family or cabbage family is a family (the third lowest primary [20] But Hopkins (1987)[22] notes mycorrhizae associated with Streptanthus glandulosus Hook. (Brassicaceae), a non-accumulator. Some fungi tolerate easily the generally elevated metal contents of serpentine soils. Some of these fungal species are mycorrhizal[23]. High levels of phosphate in the soil inhibit mycorrhizal growth[24].

The uptake of radionuclides by fungi depends on its nutritional mechanism (mycorrhizal or saprotrophic)[25]. A mycorrhiza (Greek for fungus roots coined by Frank 1885 typically seen in the plural forms mycorrhizae or mycorrhizas) is a symbiotic (occasionally Pleurotus eryngii absorbs Cs best over Sr and Co, while Hebeloma cylindrosporum favours Co. But increasing the amount of K increases the uptake of Sr (chemical analogue to Ca) but not that of Cs (chemical analogue to K). Moreover, the uptake of Cs decreases with Pleurotus eryngii (mycorrhizal) and Hebeloma cylindrosporum (saprotrophic) if the Cs content is increased, but that of Sr increases if its content is increased – this would indicate that the uptake is independent from the nutritional mechanism.

2 - Pollen and seed dispersal

Some animals obtain food from the plant (nectar, pollen, or fruit pulp - Howe & Westley 1988). Animals feeding from hyperaccumulors high in metal content must either be metal-tolerant or dilute it with a mixed diet. Alternatively hyperaccumulators may rely on abiotic vectors or non-mutualistic animal vectors for pollen or seed transport, but we lack information on seed and pollen dispersal mechanisms for hyperaccumulating plants.

Jaffré & Schmid 1974; Jaffré et al. 1976; Reeves et al. 1981; have studied metal contents of entire flowers and/or fruits. They have recorded elevated metal levels in these. We find an exception with Walsura monophylla Elm. (Meliaceae), originating from the Philippines and showing 7000 mg/kg Ni in leaves but only 54 mg/kg in fruits[26]. Some plants may thus have a mechanism by which metal or other contaminants is excluded from their reproductive structures.

Commensalism

This is an interaction benefiting one organism while being of neutral value to another. The most likely one with hyperaccumulators would be epiphytism. But this is most noticeable in humid habitats, whereas only a few detailed field studies of hyperaccumulators have been conducted in such habitats, and those studies (mostly to do with humid tropical forests on serpentine soils) pay little or no attention to that point (e. g. , Proctor et al. 1989; Baker et al. 1992). Proctor et al. (1988) studied the tree Shorea tenuiramulosa, which can accumulate up to 1000 mg Ni/kg dry weight in leaf material. They estimated covers of epiphytes on the boles of trees in Malaysia, but did not report values for individual species. Boyd et al. (1999) studied the occurrence of epiphytes on leaves of the Ni hyperaccumulating tropical shrub Psychotria douarrei (Beauvis. ). Epiphyte load increased significantly with increasing leaf age, up to 62% for the oldest leaves. An epiphyte sample of leafy liverworts removed from P. douarrei, was found to contain 400 mg Ni /kg dry weight (far less than the host plant, whose oldest and most heavily epiphytized leaves contained a mean value of 32,000 mg Ni/kg dry weight). High doses of Ni therefore do not prevent colonization of Psychotria douarrei by epiphytes.

Chemicals that mediate host-epiphyte interactions are most likely to be located in the outermost tissues of the host (Gustafsson & Eriksson 1995). Also, most of the metal accumulates in epidermal or subepidermal cell walls or vacuoles (Ernst & Weinert 1972; Vazquez et al. 1994; Mesjasz- Rzybylowicz et al. 1996; Gabrielli et al. 1997). These findings suggest that epiphytes would experience higher metal levels when growing on hyperaccumulator leaves. But Severne (1974) measured the release of metal via leaching of leaves from the Ni hyperaccumulator Hybanthus floribundus (Lindl. ) F. Muell. (Violaceae) from western Australia; he concluded that its leaves do not easily leach Ni. Violaceae (alternatively Alsodeiaceae JGAgardh, Leoniaceae DC

In theory another commensal interaction could exist, if the high metal content of the soil under hyperaccumulator plants was needed for another plant species to establish itself. No evidence is known showing such effect.

The biofilm

This section needs be developed. See relevant articles on biofilm and Pseudomonas aeruginosa. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Pseudomonas aeruginosa is a Gram-negative, aerobic, rod-shaped Bacterium with unipolar motility. A biofilm is a layer of organic matter and microorganism formed by the attachment and proliferation of bacteria on the surface of the object. Biofilms are characterised by the presence of bacterial extracellular polymers glycocalyx that create a thin visible slimy layer on solid surface. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Glycocalyx is a general term referring to extracellular Polymeric material produced by some Bacteria, Epithelia and other cells

Table of hyperaccumulators

A comprehensive literature survey of hyperaccumulating plants and their uses was started by Stevie Famulari for her students at the University of New Mexico. Hyperaccumulators table – 1 It is now considerably increased in size and has had to be split into 3 sections:

References

  1. ^ Meagher, RB (2000). Hyperaccumulators table – 1 This section covers known Nickel hyperaccumulators accumulators or species tolerant to nickel This section covers Radionuclides hydrocarbures and organic solvents and information on the plants used for their remediation "Phytoremediation of toxic elemental and organic pollutants". CURRENT OPINION IN PLANT BIOLOGY 3 (2): 153-162. PMID 10712958.  
  2. ^ Mendez MO, Maier RM (2008). "Phytostabilization of mine tailings in arid and semiarid environments—an emerging remediation technology". Environ Health Perspect 116 (3): 278–83. doi:10.1289/ehp.10608. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  3. ^ Murali Subramanian, David J. Oliver, and Jacqueline V. Shanks. TNT Phytotransformation Pathway Characteristics in Arabidopsis: Role of Aromatic Hydroxylamines. Biotechnol. Prog. , 22 (1), 208 -216, 2006.
  4. ^ Hannink N, Rosser SJ, French CE, Basran A, Murray JA, Nicklin S, Bruce NC. Phytodetoxification of TNT by transgenic plants expressing a bacterial nitroreductase. 1: Nat Biotechnol. 2001 Dec;19(12):1168-72.
  5. ^ a b c d e [1] The significance of metal hyperaccumulation for biotic interactions, by R. S. Boyd and S. N. Martens. Chemoecology 8 (1998) pp. 1–7
  6. ^ a b A. J. M. Baker, R. R. Brooks. Terrestrial higher plants which hyperaccumulate metallic elements – A review of their distribution, ecology and phytochemistry. Biorecovery (1989), 1:81–126
  7. ^ [2] M. A. Davis, J. F. Murphy, and R. S. Boyd. Nickel Increases Susceptibility of a Nickel Hyperaccumulator to Turnip mosaic virus. J. Environ. Qual. , Vol. 30, January–February 2001
  8. ^ D. Mishra, M. Kar. Nickel in plant growth and metabolism. Bot Rev (1974), 40:395–452
  9. ^ S. P. Hopkin. Ecophysiology of Metals in Terrestrial Invertebrates. GB-London: Elsevier Applied Science (1989)
  10. ^ P. L. Klerks. Adaptation to metals in animals. pp 313–321 in Shaw AJ (ed. ) Heavy Metal Tolerance in Plants: Evolutionary Aspects. Boca Raton:FL: CRC Press (1990)
  11. ^ a b M. T. Brown et I. R. Hall. Ecophysiology of metal uptake by tolerant plants. Pp 95–104 in Shaw AJ (ed. ) Heavy Metal Tolerance in Plants: Evolutionary Aspects. Boca Raton: FL: CRC Press (1990)
  12. ^ R. D. MacNicol, P. H. T. Beckett. Critical tissue concentrations of potentially toxic elements. Plant Soil, 1985. 85:107–129
  13. ^ R. Gabrielli, C. Mattioni, O. Vergnano. Accumulation mechanisms and heavy metal tolerance of a nickel hyperaccumulator. Plant Nutr (1991). 14:1067–1080
  14. ^ J. B. Wilson, A. D. Q. Agnew. Positive-feedback switches in plant communities. Adv Ecol Res (1992), 23:263–336
  15. ^ T. L. Rost, M. G. Barbour, C. R. Stocking and T. M. Murphy, The root system. Plant Biology, 1998. (pp. 68-84). California: Wadsworth Publishing Company. Cited in Westhoff99.
  16. ^ R. Bradley, A. J. Burt et D. J. Read, The biology of mycorrhizal infection in the Ericaceae. VIII. The role of mycorrhizal infection in heavy metal tolerance. New Phytol 1982, 91:197–209.
  17. ^ J. L. Harley, The significance of mycorrhizae. Mycological Research 1989. 92: 129-134.
  18. ^ G. J. D. Kirk and S. Staunton. On predicting the fate of radioactive caesium in soil beneath grassland, Journal of Soil Science, 1989. 40: 71-84
  19. ^ [3] J. A. Entry, L. S. Watrud and M. Reeves, Accumulation of cesium-137 and strontium-90 from contaminated soil by three grass species inoculated with mycorrhizal fungi. Environmental Pollution, 1999. 104: 449-457. Cited in Westhoff99.
  20. ^ a b M. F. Allen. The Ecology of Mycorrhizae. New York: Cambridge University Press (1991). Cité dans Boyd 1998.
  21. ^ Marshall and Perry 1987
  22. ^ N. A. Hopkins. Mycorrhizae in a Californian serpentine grassland community. Can Bot 1987, 65:484–487
  23. ^ J. L. Maas et D. E. Stuntz. Mycoecology on serpentine soil. Mycologia 61:1106–1116 (1969). Cited in Boyd 98.
  24. ^ K. Killham. Ecology of polluted soils. Soil Ecology, 1995. (pp. 175-181) Cambridge: Cambridge University Press.
  25. ^ [4] A. Baeza, J. Guillen, S. Hernandez, A. Salas, M. Bernedo, J. L. Manjon, G. Moreno. Influence of the nutritional mechanism of fungi (mycorrhize/saprotroph) on the uptake of radionuclides by mycelium. Radiochimica acta, 2005. vol. 93, no4, pp. 233-238
  26. ^ A. J. M. Baker, J. Proctor, M. M. J. van Balgooy, R. D. Reeves. Hyperaccumulation of nickel by the flora of the ultramafics of Palawan, Republic of the Philippines. Pp 291–304 in Baker AJM, Proctor J, Reeves RD (eds) The Vegetation of Ultramafic (Serpentine) Soils. GB-Andover: Intercept (1992)

See also

External links

Bibliography

Dictionary

phytoremediation

-noun

  1. (biochemistry) bioremediation by the use of plants
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