Special Issue "Metallophytes"

A special issue of Plants (ISSN 2223-7747). This special issue belongs to the section "Plant Cell Biology".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 7798

Special Issue Editor

Dr. Celestino Quintela-Sabarís
E-Mail Website
Guest Editor
Visiting Researcher, Department of Edaphology and Chemical Agronomy, Universidade de Santiago de Compostela, Praza do Obradoiro, 0, 15705 Santiago de Compostela, A Coruña, Spain
Interests: ecology and evolution of ultramafic flora; plant–soil relationships; hyperaccumulators; agromining; phytoremediation; soil restoration

Special Issue Information

Dear Colleagues,

Metallophytes (i.e., plants able to survive on metal-rich soils) are botanical rarities. Through the evolution of different mechanisms for handling trace elements (‘metals’), some metallophytes are able to exclude metals from their aerial parts until a certain toxicity threshold is exceeded, whereas others have the ability to uptake and accumulate high concentrations of metals on their leaves. In hyperaccumulators, the metal foliar concentrations can be several orders of magnitude higher than normal plants growing on ‘normal’ soils. Metallophytes, either excluders or (hyper)accumulators, are interesting systems for the study of evolution, physiology and ecology of plants. Moreover, metallophytes are the basis for the phytoremediation, a suite of ecotechnological applications for the recovery of ‘metal’-polluted soils. During the last decade, there have been important advances in the understanding of physiological mechanisms of metal tolerance and accumulation, and new techniques are allowing the discovery of hyperaccumulators from biological collections and herbaria. Moreover, hyperaccumulators are being used in Albania, Greece, Malaysia, New Caledonia, and Spain to recover valuable metals (mainly Ni) in different phyto/agromining contexts.

This Special Issue on ‘Metallophytes’ in Plants welcomes research papers and reviews dedicated to the different aspects of metallophytes: reporting of new metallophyte species, ecophysiological aspects of tolerance, plant (micro)evolution on metal-rich substrates, application of metallophytes in phytoremediation or phytomining, etc. Papers dealing with non-model species, rare-earth hyperaccumulators or from low explored areas (South America, Africa) are specially welcomed.

Dr. Celestino Quintela-Sabarís
Guest Editor

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Published Papers (6 papers)

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Research

Article
Broomrape Species Parasitizing Odontarrhena lesbiaca (Brassicaceae) Individuals Act as Nickel Hyperaccumulators
Plants 2021, 10(4), 816; https://doi.org/10.3390/plants10040816 - 20 Apr 2021
Cited by 4 | Viewed by 1396
Abstract
The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between Odontarrhena lesbiaca and broomrape parasitic species, in the light of the defense hypothesis [...] Read more.
The elemental defense hypothesis supports that metal hyperaccumulation in plant tissues serves as a mechanism underpinning plant resistance to herbivores and pathogens. In this study, we investigate the interaction between Odontarrhena lesbiaca and broomrape parasitic species, in the light of the defense hypothesis of metal hyperaccumulation. Plant and soil samples collected from three serpentine sites in Lesbos, Greece were analyzed for Ni concentrations. Phelipanche nowackiana and Phelipanche nana were found to infect O. lesbiaca. In both species, Ni concentration decreased gradually from tubercles to shoots and flowers. Specimens of both species with shoot nickel concentrations above 1000 mg.kg−1 were found, showing that they act as nickel hyperaccumulators. Low values of parasite to O. lesbiaca leaf or soil nickel quotients were observed. Orobanche pubescens growing on a serpentine habitat but not in association with O. lesbiaca had very low Ni concentrations in its tissues analogous to excluder plants growing on serpentine soils. Infected O. lesbiaca individuals showed lower leaf nickel concentrations relative to the non-infected ones. Elevated leaf nickel concentration of O. lesbiaca individuals did not prevent parasitic plants to attack them and to hyperaccumulate metals to their tissues, contrary to predictions of the elemental defense hypothesis. Full article
(This article belongs to the Special Issue Metallophytes)
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Article
Intraspecific Variation in Nickel Tolerance and Hyperaccumulation among Serpentine and Limestone Populations of Odontarrhena serpyllifolia (Brassicaceae: Alysseae) from the Iberian Peninsula
Plants 2021, 10(4), 800; https://doi.org/10.3390/plants10040800 - 19 Apr 2021
Cited by 3 | Viewed by 1065
Abstract
Odontarrhena serpyllifolia (Desf.) Jord. & Fourr. (=Alyssum serpyllifolium Desf.) occurs in the Iberian Peninsula and adjacent areas on a variety of soils including both limestone and serpentine (ultramafic) substrates. Populations endemic to serpentine are known to hyperaccumulate nickel, and on account of [...] Read more.
Odontarrhena serpyllifolia (Desf.) Jord. & Fourr. (=Alyssum serpyllifolium Desf.) occurs in the Iberian Peninsula and adjacent areas on a variety of soils including both limestone and serpentine (ultramafic) substrates. Populations endemic to serpentine are known to hyperaccumulate nickel, and on account of this remarkable phenotype have, at times, been proposed for recognition as taxonomically distinct subspecies or even species. It remains unclear, however, to what extent variation in nickel hyperaccumulation within this taxon merely reflects differences in the substrate, or whether the different populations show local adaptation to their particular habitats. To help clarify the physiological basis of variation in nickel hyperaccumulation among these populations, 3 serpentine accessions and 3 limestone accessions were cultivated hydroponically under common-garden conditions incorporating a range of Ni concentrations, along with 2 closely related non-accumulator species, Clypeola jonthlaspi L. and Alyssum montanum L. As a group, serpentine accessions of O. serpyllifolia were able to tolerate Ni concentrations approximately 10-fold higher than limestone accessions, but a continuous spectrum of Ni tolerance was observed among populations, with the least tolerant serpentine accession not being significantly different from the most tolerant limestone accession. Serpentine accessions maintained relatively constant tissue concentrations of Ca, Mg, K, and Fe across the whole range of Ni exposures, whereas in the limestone accessions, these elements fluctuated widely in response to Ni toxicity. Hyperaccumulation of Ni, defined here as foliar Ni concentrations exceeding 1g kg−1 of dry biomass in plants not showing significant growth reduction, occurred in all accessions of O. serpyllifolia, but the higher Ni tolerance of serpentine accessions allowed them to hyperaccumulate more strongly. Of the reference species, C. jonthlaspi responded similarly to the limestone accessions of O. serpyllifolia, whereas A. montanum displayed by far the lowest degree of Ni tolerance and exhibited low foliar Ni concentrations, which only exceeded 1 g kg−1 in plants showing severe Ni toxicity. The continuous spectrum of physiological responses among these accessions does not lend support to segregation of the serpentine populations of O. serpyllifolia as distinct species. However, the pronounced differences in degrees of Ni tolerance, hyperaccumulation, and elemental homeostasis observed among these accessions under common-garden conditions argues for the existence of population-level adaptation to their local substrates. Full article
(This article belongs to the Special Issue Metallophytes)
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Article
A New Species of Argophyllum (Argophyllaceae) with Notes on the Species from New Caledonia and Nickel Hyperaccumulation
Plants 2021, 10(4), 701; https://doi.org/10.3390/plants10040701 - 05 Apr 2021
Cited by 1 | Viewed by 893
Abstract
The taxonomy of Argophyllum (Argophyllaceae) in New Caledonia is reviewed here. All names validly published in Argophyllum in this archipelago are discussed and lectotypified when necessary. A new species is described, Argophyllum riparium (The LSID for the name Argophyllum riparium is: 77216335-1) Pillon [...] Read more.
The taxonomy of Argophyllum (Argophyllaceae) in New Caledonia is reviewed here. All names validly published in Argophyllum in this archipelago are discussed and lectotypified when necessary. A new species is described, Argophyllum riparium (The LSID for the name Argophyllum riparium is: 77216335-1) Pillon and Hequet sp. nov. Argophyllum grunowii and A. ellipticum are both species complexes in which several species previously recognized are included here as well. Seven species are recognized in New Caledonia: A. brevipetalum, A. ellipticum, A. grunowii, A. montanum, A. nitidum, A. riparium and A. vernicosum, all endemic. Leaf nickel content of A. riparium can exceed 1000 μg·g−1, which makes this species a nickel hyperaccumulator. Measurements with a handheld X-Ray Fluorescence (XRF) spectrometer confirmed that this was also the case for all other species from New Caledonia, except A. nitidum. An identification key of New Caledonian species is provided. Full article
(This article belongs to the Special Issue Metallophytes)
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Article
Root and Shoot Response to Nickel in Hyperaccumulator and Non-Hyperaccumulator Species
Plants 2021, 10(3), 508; https://doi.org/10.3390/plants10030508 - 09 Mar 2021
Cited by 3 | Viewed by 907
Abstract
The soil–root interface is the micro-ecosystem where roots uptake metals. However, less than 10% of hyperaccumulators’ rhizosphere has been examined. The present study evaluated the root and shoot response to nickel in hyperaccumulator and non-hyperaccumulator species, through the analysis of root surface and [...] Read more.
The soil–root interface is the micro-ecosystem where roots uptake metals. However, less than 10% of hyperaccumulators’ rhizosphere has been examined. The present study evaluated the root and shoot response to nickel in hyperaccumulator and non-hyperaccumulator species, through the analysis of root surface and biomass and the ecophysiological response of the related aboveground biomass. Ni-hyperaccumulators Alyssoides utriculata (L.) Medik. and Noccaea caerulescens (J. Presl and C. Presl) F.K. Mey. and non-hyperaccumulators Alyssum montanum L. and Thlaspi arvense L. were grown in pot on Ni-spiked soil (0–1000 mg Ni kg−1, total). Development of root surfaces was analysed with ImageJ; fresh and dry root biomass was determined. Photosynthetic efficiency was performed by analysing the fluorescence of chlorophyll a to estimate the plants’ physiological conditions at the end of the treatment. Hyperaccumulators did not show a Ni-dependent decrease in root surfaces and biomass (except Ni 1000 mg kg−1 for N. caerulescens). The non-hyperaccumulator A. montanum suffers metal stress which threatens plant development, while the excluder T. arvense exhibits a positive ecophysiological response to Ni. The analysis of the root system, as a component of the rhizosphere, help to clarify the response to soil nickel and plant development under metal stress for bioremediation purposes. Full article
(This article belongs to the Special Issue Metallophytes)
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Article
Trichome Biomineralization and Soil Chemistry in Brassicaceae from Mediterranean Ultramafic and Calcareous Soils
Plants 2021, 10(2), 377; https://doi.org/10.3390/plants10020377 - 17 Feb 2021
Cited by 4 | Viewed by 1065
Abstract
Trichome biomineralization is widespread in plants but detailed chemical patterns and a possible influence of soil chemistry are poorly known. We explored this issue by investigating trichome biomineralization in 36 species of Mediterranean Brassicaceae from ultramafic and calcareous soils. Our aims were to [...] Read more.
Trichome biomineralization is widespread in plants but detailed chemical patterns and a possible influence of soil chemistry are poorly known. We explored this issue by investigating trichome biomineralization in 36 species of Mediterranean Brassicaceae from ultramafic and calcareous soils. Our aims were to chemically characterize biomineralization of different taxa, including metallophytes, under natural conditions and to investigate whether divergent Ca, Mg, Si and P-levels in the soil are reflected in trichome biomineralization and whether the elevated heavy metal concentrations lead to their integration into the mineralized cell walls. Forty-two samples were collected in the wild while a total of 6 taxa were brought into cultivation and grown in ultramafic, calcareous and standard potting soils in order to investigate an effect of soil composition on biomineralization. The sampling included numerous known hyperaccumulators of Ni. EDX microanalysis showed CaCO3 to be the dominant biomineral, often associated with considerable proportions of Mg—independent of soil type and wild versus cultivated samples. Across 6 of the 9 genera studied, trichome tips were mineralized with calcium phosphate, in Bornmuellera emarginata the P to Ca-ratio was close to that of pure apatite-calcium phosphate (Ca5(PO4)3OH). A few samples also showed biomineralization with Si, either only at the trichome tips or all over the trichome. Additionally, we found traces of Mn co-localized with calcium phosphate in Bornmuellera emarginata and traces of Ni were detected in trichomes of the Ni-hyperaccumulator Odontarrhena chalcidica. Our data from wild and cultivated plants could not confirm any major effect of soil chemistry on the chemistry of trichome biominerals. Hyperaccumulation of Ni in the plants is not mirrored in high levels of Ni in the trichomes, nor do we find large amounts of Mn. A comparison based on plants from cultivation (normal, calcareous and serpentine soils, Mg:Ca-ratios ca 1:2 to 1:20) shows at best a very weak reflection of different Mg:Ca-ratios in the mineralized trichomes. The plants studied seem to be able to maintain highly conserved biomineralization patterns across a wide range of soil chemistries. Full article
(This article belongs to the Special Issue Metallophytes)
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Article
Population Genetics of Odontarrhena (Brassicaceae) from Albania: The Effects of Anthropic Habitat Disturbance, Soil, and Altitude on a Ni-Hyperaccumulator Plant Group from a Major Serpentine Hotspot
Plants 2020, 9(12), 1686; https://doi.org/10.3390/plants9121686 - 01 Dec 2020
Cited by 6 | Viewed by 868
Abstract
Albanian taxa and populations of the genus Odontarrhena are most promising candidates for research on metal tolerance and Ni-agromining, but their genetic structure remains unknown. We investigated phylogenetic relationships and genetic differentiation in relation to distribution and ploidy of the taxa, anthropic site [...] Read more.
Albanian taxa and populations of the genus Odontarrhena are most promising candidates for research on metal tolerance and Ni-agromining, but their genetic structure remains unknown. We investigated phylogenetic relationships and genetic differentiation in relation to distribution and ploidy of the taxa, anthropic site disturbance, elevation, soil type, and trace metals at each population site. After performing DNA sequencing of selected accessions, we applied DNA-fingerprinting to analyze the genetic structure of 32 populations from ultramafic and non-ultramafic outcrops across Albania. Low sequence divergence resulted in poorly resolved phylograms, but supported affinity between the two diploid serpentine endemics O. moravensis and O. rigida. Analysis of molecular variance (AMOVA) revealed significant population differentiation, but no isolation by distance. Among-population variation was higher in polyploids than in diploids, in which genetic distances were lower. Genetic admixing at population and individual level occurred especially in the polyploids O. chalcidica, O. decipiens, and O. smolikana. Admixing increased with site disturbance. Outlier loci were higher in serpentine populations but decreased along altitude with lower drought and heat stress. Genetic variability gained by gene flow and hybridization at contact zones with “resident” species of primary ultramafic habitats promoted expansion of the tetraploid O. chalcidica across anthropogenic sites. Full article
(This article belongs to the Special Issue Metallophytes)
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