Morphological, physiological, and genetic variation between metallicolous and nonmetallicolous populations of Dianthus carthusianorum

Bacteria associated with Zn-hyperaccumulators Arabidopsis halleri and Arabidopsis arenosa from Zn-Pb-Cd waste heaps in Poland as promising tools for bioremediation

To identify metal adapted bacteria equipped with traits positively influencing the growth of two hyperaccumulator plant species Arabidopsis arenosa and Arabidopsis halleri, we isolated bacteria inhabiting rhizosphere and vegetative tissues (roots, basal and stem leaves) of plants growing on two old Zn-Pb-Cd waste heaps in Bolesław and Bukowno (S. Poland), and characterized their potential plant growth promoting (PGP) traits as well as determined metal concentrations in rhizosphere and plant tissues. To determine taxonomic position of 144 bacterial isolates, 16S rDNA Sanger sequencing was used. A metabolic characterization of isolated strains was performed in vitro using PGP tests. A. arenosa and A. halleri accumulate high amounts of Zn in their tissues, especially in stem leaves. Among in total 22 identified bacterial taxa, the highest level of the taxonomical diversity (H' = 2.01) was revealed in A. halleri basal leaf endophytes originating from Bukowno waste heap area. The 96, 98, 99, and 98% of investigated strains showed tolerant to Cd, Zn, Pb and Cu, respectively. Generally, higher percentages of bacteria could synthesize auxins, siderophores, and acetoin as well as could solubilize phosphate. Nine of waste heap origin bacterial strains were tolerant to toxic metals, showed in vitro PGP traits and are potential candidates for bioremediation.

Micro-Evolutionary Processes in Armeria maritima at Metalliferous Sites

Tolerance to heavy metals in plants is a model process used to study adaptations to extremely unfavorable environments. One species capable of colonizing areas with high contents of heavy metals is Armeria maritima (Mill.) Wild. A. maritima plants growing in metalliferous areas differ in their morphological features and tolerance levels to heavy metals compared to individuals of the same species growing in non-metalliferous areas. The A. maritima adaptations to heavy metals occur at the organismal, tissue, and cellular levels (e.g., the retention of metals in roots, enrichment of the oldest leaves with metals, accumulation of metals in trichomes, and excretion of metals by salt glands of leaf epidermis). This species also undergoes physiological and biochemical adaptations (e.g., the accumulation of metals in vacuoles of the root's tannic cells and secretion of such compounds as glutathione, organic acids, or HSP17). This work reviews the current knowledge on A. maritima adaptations to heavy metals occurring in zinc-lead waste heaps and the species' genetic variation from exposure to such habitats. A. maritima is an excellent example of microevolution processes in plants inhabiting anthropogenically changed areas.

Genetic and epigenetic variation separately contribute to range expansion and local metalliferous habitat adaptation during invasions of Chenopodium ambrosioides into China

BACKGROUND AND AIMS

Invasive plants often colonize wide-ranging geographical areas with various local microenvironments. The specific roles of epigenetic and genetic variation during such expansion are still unclear. Chenopodium ambrosioides is a well-known invasive alien species in China that can thrive in metalliferous habitats. This study aims to comprehensively understand the effects of genetic and epigenetic variation on the successful invasion of C. ambrosioides.

METHODS

We sampled 367 individuals from 21 heavy metal-contaminated and uncontaminated sites with a wide geographical distribution in regions of China. We obtained environmental factors of these sampling sites, including 13 meteorological factors and the contents of four heavy metals in soils. Microsatellite markers were used to investigate the demographic history of C. ambrosioides populations in China. We also analysed the effect of epigenetic variation on metalliferous microhabitat adaptation using methylation-sensitive amplified polymorphism (MSAP) markers. A common garden experiment was conducted to compare heritable phenotypic variations among populations.

KEY RESULTS

Two distinct genetic clusters that diverged thousands of years ago were identified, suggesting that the eastern and south-western C. ambrosioides populations in China may have originated from independent introduction events without recombination. Genetic variation was shown to be a dominant determinant of phenotypic differentiation relative to epigenetic variation, and further affected the geographical distribution pattern of invasive C. ambrosioides. The global DNA unmethylation level was reduced in metalliferous habitats. Dozens of methylated loci were significantly associated with the heavy metal accumulation trait of C. ambrosioides and may contribute to coping with metalliferous microenvironments.

CONCLUSIONS

Our study of C. ambrosioides highlighted the dominant roles of genetic variation in large geographical range expansion and epigenetic variation in local metalliferous habitat adaptation.

Survival on railway tracks of Geranium robertianum-a glyphosate-tolerant plant

Geranium robertianum is a herbaceous plant that prefers shady and fertile forest habitats. However, it also occurs on railway tracks, where there are difficult conditions for plant growth and regular herbicide spraying (in high concentrations, twice a year). One of the most commonly used herbicides in railway areas is glyphosate. The effect of the glyphosate on the G. robertianum plants found on railway tracks and in nearby forests in north-eastern Poland was checked. The aim of the study was to explain how G. robertianum can survive on railway tracks despite spraying with the glyphosate. Increased tolerance to the glyphosate of the G. robertianum plants from track populations was demonstrated compared to the plants from forest populations that had not previously been in contact with the herbicide. After 35 days after treatment with the herbicide, 75% of the plants from the observed forest populations withered, while only 38% did from the track populations. Ultrastructure of plant leaf cells from forest populations was strongly disturbed, which was not observed in plants from track populations. It was also shown that plants from track populations accumulated more glyphosate and AMPA in their tissues than plants from forest populations. The obtained results indicate that long-term use of herbicides may cause formation of biotypes of plants resistant to a given herbicide. This fact explains the possibility of G. robertianum occurring on railway tracks, despite spraying with the glyphosate. It is also a manifestation of microevolutionary processes.

Distinct co-tolerance responses to combined salinity and cadmium exposure in metallicolous and non-metallicolous ecotypes of Silene vulgaris

This study compared co-tolerance to salinity and cadmium and investigated its mechanisms in a facultative metallophyte Silene vulgaris originating from distinct habitats. Shoots of calamine (Cal) and non-metallicolous (N-Cal) ecotypes grown in vitro were exposed to 10 and 100 mM NaCl, 5 μM CdCl₂ and their combinations. Stress effects were evaluated based on growth, oxidative stress parameters, and DNA content and damage. Tolerance mechanisms were assessed by analyzing non-enzymatic antioxidants, osmolytes and ion accumulation. Irrespective of the ecotype, Cd stimulated shoot proliferation (micropropagation coefficients MC = 15.2 and 12.1 for Cal and N-Cal, respectively, growth tolerance index GTI = 148.1 and 156.7%). In Cal ecotype this was attributed to an increase in glutathione content and reorganization of cell membrane structures under Cd exposure, whereas in N-Cal to enhanced synthesis of other non-enzymatic antioxidants, mainly carotenoids and ascorbate. Low salinity stimulated growth of Cal ecotype due to optimizing Cl^- content. High salinity inhibited growth, especially in Cal ecotype, where it enhanced DNA damage and disturbed ionic homeostasis. Species-specific reaction to combined salinity and Cd involved a mutual inhibition of Na⁺, Cl^- and Cd²⁺ uptake. N-Cal ecotype responded to combined stresses by enhancing its antioxidant defense, presumably induced by Cd, whereas the metallicolous ecotype triggered osmotic adjustment. The study revealed that in S. vulgaris Cd application ameliorated metabolic responses to simultaneous salinity exposure. It also shed a light on distinct strategies of coping with combined abiotic stresses in two ecotypes of the species showing high plasticity in environmental conditions.

Evolutionary dynamics of quantitative variation in an adaptive trait at the regional scale: The case of zinc hyperaccumulation in Arabidopsis halleri

Metal hyperaccumulation in plants is an ecological trait whose biological significance remains debated, in particular because the selective pressures that govern its evolutionary dynamics are complex. One of the possible causes of quantitative variation in hyperaccumulation may be local adaptation to metalliferous soils. Here, we explored the population genetic structure of Arabidopsis halleri at fourteen metalliferous and nonmetalliferous sampling sites in southern Poland. The results were integrated with a quantitative assessment of variation in zinc hyperaccumulation to trace local adaptation. We identified a clear hierarchical structure with two distinct genetic groups at the upper level of clustering. Interestingly, these groups corresponded to different geographic subregions, rather than to ecological types (i.e., metallicolous vs. nonmetallicolous). Also, approximate Bayesian computation analyses suggested that the current distribution of A. halleri in southern Poland could be relictual as a result of habitat fragmentation caused by climatic shifts during the Holocene, rather than due to recent colonization of industrially polluted sites. In addition, we find evidence that some nonmetallicolous lowland populations may have actually derived from metallicolous populations. Meanwhile, the distribution of quantitative variation in zinc hyperaccumulation did separate metallicolous and nonmetallicolous accessions, indicating more recent adaptive evolution and diversifying selection between metalliferous and nonmetalliferous habitats. This suggests that zinc hyperaccumulation evolves both ways-towards higher levels at nonmetalliferous sites and lower levels at metalliferous sites. Our results open a new perspective on possible evolutionary relationships between A. halleri edaphic types that may inspire future genetic studies of quantitative variation in metal hyperaccumulation.

Variations in several morphological characteristics and Cd/Pb accumulation capacities among different ecotypes of torpedograss responding to Cd-Pb stresses

Torpedograss (Panicum repens) has been recognized as an useful plant species for phytoremediation of water-level-fluctuation zones, which is a worldwide challenge. In this study, 10 ecotypes collected from tropical zone and flooded habitats (Group A) and subtropical zone and drought habitats (Group B) were used to clarify their responses to Cd-Pb stresses and effects of long-term adaptation on their morphological features and Cd-Pb accumulation capacities. Branch capacity, shoot and root biomasses of Group A under control were smaller than those of Group B, while the opposite results were observed under Cd-Pb stresses. The average plant shoot Cd concentrations of Group A under L-Cd-Pb and H-Cd-Pb were 24.84 and 52.38 mg kg^-1, respectively, significantly lower than those of Group B (36.81 and 67.60 mg kg^-1), while the variation among each group was insignificant, suggesting that habitat isolation and long-term adaptation may have led to differentiation in morphological features and metal uptake capacity. Torpedograss possesses high tolerance to Cd-Pb toxicities, and those ecotypes with larger biomass had higher Cd-Pb accumulation capacities. Torpedograss is a potential plant species for Cd phytoremediation and approximately 16 years would be required to clean soil contained by Cd as high as 10 mg kg^-1 using the selected torpedograss ecotypes.

From laboratory to field studies - The assessment of Biscutella laevigata suitability to biological reclamation of areas contaminated with lead and cadmium

The aim of the work was to evaluate the usefulness of the in vitro multiplication of Biscutella laevigata calamine ecotype for in situ reclamation of post-flotation wastes polluted with Pb and Cd. The experiment was conducted on three steps: (i) plant shoots' production under in vitro condition, (ii) establishment of the material in greenhouse experiment, and finally (iii) field cultivation directly on the mining-waste heap of Olkusz Ore-Bearing Region, Poland. This region is known to be one of the most chemically-degraded area in central Europe. The laboratory-set in vitro analysis enabled to obtain the high-quality plant shoots, which multiply the most effectively (with growth tolerance index 130-150%) on medium containing 5.0μM CdCl₂ and 0.5mM Pb(NO₃)₂. These plants were used for the next two ex vitro experiments. Several biometric and physiological analysis (i.e. of photosystem II activity F_v/F_m and PI, photosynthetic pigment contents) were done to indicate plant physiological status during these experiments. The main novelty of the work was to prove that in vitro-multiplied shoots of B. laevigata - the representative of native flora from Olkusz Ore-Bearing Region - can be successfully implemented in situ for the restoration of these degraded area. Moreover, the addition of sewage sludge as a source of organic compounds significantly improved plants' growth and development what is especially important due to the lack of other legal solutions for the management of the sewage sludge in some countries.

Comparison of Analytical Methods in Chemometric Fingerprinting of Metallicolous and Non-metallicolous Populations of Echium vulgare L

INTRODUCTION

Adverse environmental conditions usually change plant biochemical pathways resulting in accumulation or decreased content of both primary and secondary metabolites. The chemometric fingerprinting analysis proves to be a useful tool to reveal phytochemical differentiation between plants inhabiting heavy metal-contaminated and uncontaminated areas.

OBJECTIVE

Development and assessment of four analytical techniques - high performance capillary electrophoresis (HPCE), thin-layer chromatography (TLC), mass spectrometry (MS), and Fourier transform infrared (FTIR) spectroscopy in chemometric fingerprinting of metallicolous and non-metallicolous populations of Echium vulgare L.

MATERIAL AND METHODS

Twenty-one crude methanol extracts of shoot samples representing three populations of Echium vulgare L., two originating from highly metal polluted areas and one from an unpolluted area, were investigated using four analytical methods: HPCE, TLC, MS, and FTIR spectroscopy. Data pre-processing (denoising, background subtracting, horizontal alignment) followed by principal component analysis (PCA), hierarchical clustering analysis (HCA), and phytochemical difference index (DI) calculations facilitated exploration of the differences and similarities between the populations.

RESULTS

Clear phytochemical divergence between metallicolous and non-metallicolous populations of Echium vulgare was found. The suitability of the analytical techniques for revealing phytochemical markers and discrimination of individuals originating from different populations differed and in general increased in the order: TLC < MS = HPCE < FTIR.

CONCLUSION

The chemometric methods applied were successful in discrimination between samples from polluted and unpolluted areas, showing a potential perspective for environmental quality control. Copyright © 2016 John Wiley & Sons, Ltd.

Geography Plays a More Important Role than Soil Composition on Structuring Genetic Variation of Pseudometallophyte Commelina communis

Pseudometallophytes are excellent models to study microevolution and local adaptation to soil pollution, as they can grow both on metalliferous and contrasting non-metalliferous soils. Although, there has been accumulating evidence for the effects of edaphic conditions and geographical isolation on the genetic structure of pesudometallophytes, it is still a difficult problem in evolutionary biology to assess their relative importance. In this study, we investigated the spatial patterns of genetic variability, population differentiation and genetic groups in pseudometallophyte Commelina communis with 12 microsatellite loci. Eight metallicolous and six non-metallicolous populations of C. communis were sampled from cupriferous sites and surrounding non-contaminated areas in China. Neither significant reduction in genetic diversity nor apparent founder and bottleneck effects were observed in metallicolous populations of C. communis. Based on Bayesian and Neighbor-Joining clustering analyses and a principal coordinates analysis, all sampled populations were found to be mainly separated into three genetic groups, corresponding well to their geographical locations rather than edaphic origins. Moreover, a significant and strong correlation between population genetic divergence and geographical distance were detected by Mantel test (r = 0.33; P < 0.05) and multiple matrix regression with randomization (MMRR; βD = 0.57, P < 0.01). However, the effect of copper concentration on genetic patterns of C. communis was not significant (MMRR; βE = -0.17, P = 0.12). Our study clearly demonstrated that the extreme edaphic conditions in metalliferous areas had limited effects on the genetic variability in C. communis. Geographic distance played a more important role in affecting the genetic structure of C. communis than soil composition did. In C. communis, the geographically disjunctive populations on metalliferous soils had multiple origins and evolved independently from nearby non-metallicolous populations.

Naturally evolved enhanced Cd tolerance of Dianthus carthusianorum L. is not related to accumulation of thiol peptides and organic acids

Two contrasting ecotypes of Dianthus carthusianorum L., metallicolous (M) and nonmetallicolous (NM), were cultivated in hydroponics at 0-50 μM Cd for 14 days to compare their Cd accumulation, sensitivity and tolerance mechanisms. While both ecotypes contained similar concentrations of Cd in the shoots and roots, the M ecotype was more Cd-tolerant (as measured by fresh weight production and root and leaf viability). Both ecotypes accumulated phytochelatins (PCs) in response to Cd with a higher amount thereof found in the NM ecotype. Concentrations of PCs remained unchanged with increasing Cd concentrations in the root tissues, but their content in the shoots increased. The addition of L-buthionine-sulfoximine (BSO) diminished glutathione (GSH) accumulation and arrested PC production, which increased the sensitivity to Cd of the NM, but not M ecotype. Organic acids (malate and citrate) as well as proline accumulation did not change significantly after Cd exposition and was at the same level in both ecotypes. The enhanced Cd tolerance of the M ecotype of D. carthusianorum cannot be explained in terms of restricted Cd uptake and differential production of PCs, organic acids or proline; some other mechanisms must be involved in its adaptation to the high Cd content in the environment.

Effect of cadmium on selected physiological and morphological parameters in metallicolous and non-metallicolous populations of Echium vulgare L

Cadmium tolerance of three populations of Echium vulgare L., naturally occurring on two Zn-Pb waste deposits (metallicolous populations M1, M2) and on an uncontaminated site (non-metallicolous population, NM) was investigated. The plants were cultivated in hydroponics at 0, 5, 15, 30, or 50μM Cd for 14 days. Although Cd reduced the content of photosynthetic pigments indifferently in the three populations, plant growth parameters and root viability analyses confirmed different Cd tolerances decreasing in the order M1>M2>NM in the populations studied. Organic acids (tartrate, malate, citrate, succinate) were not responsible for the elevated Cd tolerance of the metallicolous populations, although malate and citrate might participate in Cd detoxification in the roots of the M1 and M2. Phytochelatin concentrations were higher in the roots of M1 and M2 populations of E. vulgare, suggesting their role in Cd detoxification and different Cd tolerances.

Accumulation and tolerance of lead in two contrasting ecotypes of Dianthus carthusianorum

Dianthus carthusianorum is one of the dominant plant species colonising the Zn-Pb waste deposits in Bolesław, Southern Poland. It differs in terms of morphology and genetics from ecotypes inhabiting non-metal-polluted areas. The response of waste-heap (metallicolous, M) and reference (nonmetallicolous, NM) ecotypes of D. carthusianorum to Pb in hydroponics was investigated and compared in this study. The plants of the M ecotype were more tolerant to Pb than these of the NM ecotype in spite of accumulation of higher concentrations of Pb. In both ecotypes, about 70-78% of Pb was retained in roots. In non Pb-treated plants, a higher glutathione (GSH) level was found in the M ecotype. After the Pb exposure, the GSH level decreased and was similar in both ecotypes. Lead treatment induced synthesis of phytochelatins (PCs) only in the plant roots, with significantly higher concentrations thereof detected in the NM ecotype. Malate and citrate concentrations were higher in the M ecotype; however, they did not change significantly upon any Pb treatment in either ecotype. The results indicated that neither PCs nor organic acids were responsible for the enhanced Pb tolerance of the waste-heap plants.