Seasonal changes in antioxidative/oxidative profile of mining and non-mining populations of Syrian beancaper as determined by soil conditions

Transcriptomic analysis revealing the molecular response to arsenic stress in desert Eremostachys moluccelloides Bunge

The saline, alkaline environment of arid soils is conducive to the diffusion of the metalloid arsenic (As). Desert plants in this area are of great ecological importance and practical value. However, there are few studies on the mechanism of arsenic action in desert plants. Therefore, in this study, Eremostachys moluccelloides Bunge was treated with different concentrations of As2O5 [As(V)] to analyze the physiological, biochemical, and transcriptomic changes of its roots and leaves and to explore the molecular mechanism of its response to As(Ⅴ) stress. The activities of catalase, superoxidase, peroxidase, and the contents of malondialdehyde and proline in roots and leaves first increased and then decreased under the As(Ⅴ) stress of different concentrations. The content of As was higher in roots than in leaves, and the As content was positively correlated with As(Ⅴ) stress concentration. In the differentially expressed gene analysis, the key enzymes of the oxidative stress response in roots and leaves were significantly enriched in the GO classification. In the KEGG pathway, genes related to the abscisic acid signal transduction pathway were co-enriched and up-regulated in roots and leaves. The related genes in the phenylpropanoid biosynthesis pathway were significantly enriched and down-regulated only in roots. In addition, the transcription factors NAC, HB-HD-ZIP, and NF-Y were up-regulated in roots and leaves. These results suggest that the higher the As(V) stress concentration, the more As is taken up by roots and leaves of E. molucelloides Bunge. In addition to causing greater oxidative damage, this may interfere with the production of secondary metabolites. Moreover, it may improve As(V) tolerance by regulating abscisic acid and transcription factors. The results will deepen our understanding of the molecular mechanism of As(Ⅴ) response in E. moluccelloides Bunge, lay the foundation for developing and applying desert plants, and provide new ideas for the phytoremediation of As pollution in arid areas.

Revegetation of mining-impacted sites with a tropical native grass: Constraints of climate seasonality and trace-element accumulation

The iron ore mining activity results in considerable waste production and impacts on surrounding ecosystems. Natural recovery of impacted areas is absent or occurs slowly, especially when associated with prolonged dry seasons in tropical regions. The objective of this work was to unveil the mechanisms of Paspalum densum (Poir.) grass to overcome the periods of seasonal drought and its metal accumulation in areas impacted by iron mining, a tailings storage facilities and surrounding ferruginous grassland in Brazil. Lower mortality was observed among individuals in the tailings storage facilities, with a 74.3% survival rate. In contrast, after the beginning of the dry season, all individuals died in the ferruginous grassland. The plants in the tailings deposits showed better nutrition, with a higher concentration of P, Cu, Fe, Zn, Mn and greater capacity to accumulate Pb and Cd over time. Pb was the element with highest bioconcetration factor (BCF) and bioaccumulation coefficient (BAC), while Mn was the one with the highest translocation factor (TF). The dry season resulted in reduced chlorophyll a, b and total and effective quantum yield of photosystem II (PSII) of P. densum individuals. However, the plants in the tailings storage facilities showed adjustments to overcome the effects of drought, with an increase in the concentration of proline in leaves and reduction of oxidative damage (MDA and H₂O₂) at the end of the dry season. The grass P. densum showed rapid acclimatization in the tailings storage facilities and resistance to drought through antioxidant and photosynthetic adjustments and was still able to bioaccumulate and translocate in plant tissues some metals present in the iron ore impacted sites.

Characterization of ectomycorrhizal fungal communities associated with tree species on an iron tailings deposit undergoing restoration

Vegetation restoration is an effective method to improve the ecological environment of mine tailings, which has a profound impact on the potential ecological functions of soil fungal communities; yet, little is known about its beneficial effect on soil ectomycorrhizal fungal community. In this study, the responses of soil characteristics and soil ectomycorrhizal fungal community diversity and structure to different revegetation, as well as the contribution of soil factors to soil ectomycorrhizal community were investigated in Liaoning Province, China. As we anticipated, the presence of vegetation significantly improved most soil properties we studied. What's more, compared to Korean pine (Pinus koraiensis Sieb. et Zucc.), Chinese poplar (Populus simonii Carr), and black locust (Robinia pseudoacacia L) could better improve soil total carbon, total nitrogen, total phosphorus, and available phosphorus. In addition, soil ectomycorrhizal fungal community diversity in black locust was greater than Korean pine and Populus simonii. Nonmetric multidimensional scaling analyses indicated that soil ectomycorrhizal community significantly differed depending on different revegetation types. Thus, these results indicated that black locust could be a suitable species for the revegetation of iron mine tailings. The study provided theoretical basis for ecological restoration of iron mine tailings using local plant species.

Response of Phragmites australis to increasing As(V) concentrations: Accumulation and speciation of As, and plant oxidative stress

The use of macrophytes has been proposed recently as a suitable option for the phytostabilization or rhizofiltration of soils or waters contaminated by trace elements. As one of the most representative species of this type of plant, common reed (Phragmites australis (Cav.) Trin. ex Steud.) has shown tolerance to high concentrations of potentially hazardous elements, as is the case of arsenic. However, a deeper knowledge of how these plants deal with this toxicity, including their oxidative response, is needed for the optimum utilization of this species in phytoremediation procedures. In fact, little is known about how common reed plants react to As toxicity or the tolerance limits and accumulation potential of this species. In this work, common reed plants were exposed to a range of As(V) mass concentrations (0.5-10 mg L^-1) in a hydroponic experiment, and the performance of the plants (growth, photosynthetic pigments, and oxidative stress related parameters) was evaluated and related to the major As species present in the different parts of the plants. The plants did not show any apparent symptom of toxicity and no significant effects were found for any of the different plant parameters analyzed. Arsenic was mostly accumulated as As(III) in the roots of the plants, and almost no translocation to the aerial part of the plants was observed for any of the As species analyzed. Common reed has shown a high capacity for As accumulation in its roots with no signs of toxicity, despite small nutrient imbalances. Thus, it can be considered to be a good candidate for use in the rhizofiltration and phytostabilization of As contaminated waters and soils, respectively.

Genotoxicity and Cytotoxicity Induced in Zygophyllum fabago by Low Pb Doses Depends on the Population’s Redox Plasticity

Lead (Pb) soil contamination remains a major ecological challenge. Zygophyllum fabago is a candidate for the Pb phytostabilisation of mining tailings; nevertheless, the cytogenotoxic effects of low doses of Pb on this species are still unknown. Therefore, Z. fabago seeds collected from non-mining (NM) and mining (M) areas were exposed to 0, 5 and 20 µM Pb for four weeks, after which seedling growth, Pb cytogenotoxic effects and redox status were analyzed. The data revealed that Pb did not affect seedling growth in M populations, in contrast to the NM population. Cell cycle progression delay/arrest was detected in both NM and M seedlings, mostly in the roots. DNA damage (DNAd) was induced by Pb, particularly in NM seedlings. In contrast, M populations, which showed a higher Pb content, exhibited lower levels of DNAd and protein oxidation, together with higher levels of antioxidants. Upon Pb exposure, reduced glutathione (GSH) and non-protein thiols were upregulated in shoots and were unaffected/decreased in roots from the NM population, whereas M populations maintained higher levels of flavanols and hydroxycinnamic acids in shoots and triggered GSH in roots and shoots. These differential organ-specific mechanisms seem to be a competitive strategy that allows M populations to overcome Pb toxicity, contrarily to NM, thus stressing the importance of seed provenance in phytostabilisation programs.

Response of Three Miscanthus × giganteus Cultivars to Toxic Elements Stress: Part 1, Plant Defence Mechanisms

Miscanthus × giganteus demonstrated good phytostabilization potentials in toxic element (TE) contaminated soils. However, information about its tolerance to elevated concentrations is still scarce. Therefore, an ex-situ pot experiment was launched using three cultivars (termed B, U, and A) grown in soils with a gradient Cd, Pb and Zn concentrations. Control plants were also cultivated in non-contaminated soil. Results show that the number of tillers per plant, stem diameter as well as leaf photosynthetic pigments (chlorophyll a, b and carotenoids) were negatively impacted by soil contamination. On the other hand, phenolic compounds, flavonoids, tannins, and anthocyanins levels along with the antioxidant enzymatic activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase increased in the plants grown on contaminated soils. Altogether, these data demonstrate that miscanthus is impacted by concentrations of toxic elements yet is able to tolerate high levels of soil contamination. These results may contribute to clarifying the miscanthus tolerance strategy against high contamination levels and its efficiency in phytoremediation.

Reclamation competence of Crotalaria juncea with the amalgamation and influence of indigenous bacteria on a waste dump of bauxite mine

The accumulated bauxite mine soil had an acidic pH of 5.52 ± 0.12 and more heavy metals such as Cr, Cd, Zn, and Pb, which can cause severe soil and water pollution to the nearby farmlands and water reservoirs. Hence, the work was designed to find the possibility of reclamation of bauxite mine soil through Crotalaria juncea with the amalgamation of native metal degrading bacterial isolates. Out of 15 bacterial cultures, only 2 isolates (B3 and B14) showed excellent metal tolerance (for up to 750 mg L^-1), solubilizing (15.27-38.7 mg kg^-1) (including phosphate: 47.4 ± 1.79%), and degrading potential (22.8 ± 0.89 to 31.5 ± 1.6%) than the others. These B3 and B14 isolates were recognized as B. borstelensis UTM105 (1432 bp) and B. borstelensis AK2 (1494 bp) through molecular characterization. These isolates have produced a metal stress response protein (205-43 KDa molecular weight protein) during metal stress conditions. The phytoremediation competence of C. juncea under the influence of these bacterial isolates was assessed with various treatment (I-IV) schemes. The treatment IV (C. juncea with two bacterial isolates) showed substantial physiological and biochemical results compared with the control and the other treatments. The phytoremediation competence of C. juncea was also effective in treatment IV than the others. It reduced and extracted a reasonable quantity of metals from the bauxite mine soil. The intact results accomplished that these native metals tolerant, solubilizing, and degrading bacterial isolates, could be used as optimistic bacterial candidates in combination with C. juncea for the effective reclamation of metal enriched bauxite mine soil.

Do Old Mining Areas Represent an Environmental Problem and Health Risk? A Critical Discussion through a Particular Case

A bibliographic review was carried out to establish the state of knowledge of a mining area with several centuries of exploitation and currently abandoned. The selected case study, the Sierra Minera de Cartagena-La Union (Spain), has a long history of mining activity, ending in 1990. The area is rich in metallic sulphide (lead, zinc and iron), with underground mines and quarries. The zone is very close to important populations and affects protected sites of special ecological value. It is also adjacent to areas dedicated to agriculture and important centres of tourist interest. It is a territory that meets the requirements to be classified as a critical area, as it is in a state of unstable physical and geochemical equilibrium, giving rise to possible risks to human health and ecosystems. A literature review was carried out according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) methodology criteria, consulting a large number of related publications. The results obtained using the Source-Pathway-Receptor model make it possible to identify the main impacts caused by the contamination sources, the main routes of contamination, as well as the transfer to the biota and the influence on adjacent agricultural soils. In this study, lead, cadmium, zinc, arsenic, copper and manganese were considered as potential toxic elements (PTEs), and data were obtained on concentrations in soil, water and air as well as in fauna and flora. Finally, once the receptors and the associated risks to the ecosystem and human health were identified, a conceptual model of the contamination was drawn up to consider a management proposal to tackle the problems associated with this area, which would also be applicable to critical mining zones.

Pb tolerance and accumulation capabilities of Bidens pilosa L. growing in polluted soils depend on the history of exposure

Phytoremediation, especially phytoextraction, is a good alternative for remediation of soils contaminated with heavy metals. This method requires selection of species for their tolerance, high accumulation levels in harvestable parts, and high biomass production. Bidens pilosa L. has been reported as tolerant to and potentially hyperaccumulator of several heavy metals, including Pb, but with variable results in terms of effectiveness. The aim of this study was to analyse the intra- and interpopulation variability of B. pilosa in response to Pb in individuals from two populations: one historically exposed to Pb and another with no history of exposure. Bidens pilosa L. presented tolerance to Pb pollution in soil, evidenced in a higher survival rate, a better antioxidant response, and an efficient reduction in cell membrane damage mainly due to history of exposure. The period of exposure (30 years) was not long enough to obtain a B. pilosa population that provides seeds for phytoextraction projects, since the average value of total extraction was relatively low. Collecting seeds from a historically exposed population will provide some suitable individuals with Pb accumulation and translocation capabilities, but not a sufficient amount to conduct a large phytoremediation project. The individual accumulator profile of B. pilosa is not related to the physiological behaviour or to the Pb entry into the vascular bundle in root, but to the incorporation of other heavy metals that are micronutrients.

How does drought affect native grasses' photosynthesis on the revegetation of iron ore tailings?

The revegetation of areas degraded by iron ore mining is a difficult challenge mainly due to water availability and impoverished metal-rich substrates. We sought to understand the photosynthetic responses to drought of native tropical grasses Paspalum densum (Poir.) and Setaria parviflora (Poir.) grown in iron ore tailing. The grass P. densum presented better photosynthetic adjustments when grown in the iron ore tailing and S. paviflora in response to water stress. Both species accumulated iron above the phytotoxic threshold when grown in an iron ore tailing. The net photosynthesis, stomatal conductance, transpiration, and water use efficiency decreased followed by a reduction in leaf relative water content in response to water stress for both species. The photochemical efficiency of photosystem II only decreased at the point of maximum drought. At this point, the water-stressed grass grown in the iron ore tailing presented higher H₂O₂ concentrations, particularly S. parviflora. After rehydration, full recovery of photosynthetic variables was achieved with decreased malondialdehyde concentrations, increased catalase activity, and, consequently, decreased H₂O₂ concentrations in leaves for both species. The fast recovery of the native grasses P. densum and S. parviflora to drought in the iron ore tailing substrate is indicative of their resistance and potential use in the revegetation of impoverished mined areas with high iron content and seasonal water deficit.

OPDA and ABA accumulation in Pb-stressed Zygophyllum fabago can be primed by salicylic acid and coincides with organ-specific differences in accumulation of phenolics

Salicylic acid (SA) is a well-known priming agent that is widely used to protect plants against stressing agents, including heavy metals as Pb. A better understanding of the mechanisms that enable plants to counteract Pb toxicity would help to select strategies for land reclamation programs. Here we used a metallicolous population of Zygophyllum fabago to assess the extent to which SA pretreatment modulates Pb-induced changes in phenol metabolism and stress-related phytohormone levels in roots and leaves. Our data revealed that accumulation of different phytohormones, lignin, soluble and wall-bound phenolics as well as peroxidase (PRX) activity in Pb-stressed plants differed after SA-pretreatment. Exposure to Pb led to the induction of soluble and cell wall-bound PRX activities, particularly those involved in the oxidation of coniferyl alcohol and ferulic acid, while pretreatment with SA reduced the Pb-induced stimulation of PRX activities in roots but increased them in leaves. SA-treatment by itself induced accumulation of ABA and the JA-precursor 12-oxo-phytodienoic acid (OPDA) in the roots. Pb in turn inhibited these SA-induced effects with the exception of OPDA accumulation that was primed by the pretreatment. The SA treatment also induced accumulation of OPDA in leaves but suppressed the accumulation of JA-Ile although with relatively small absolute changes. Notably, Pb-induced accumulation of ABA was primed in the leaves of SA-pretreated plants. Together our data suggest that priming of OPDA accumulation in the roots and of ABA in the leaves by SA-pretreatment may play important regulatory roles, possibly via regulating PRX activities, for Pb stress in plants.

Plant Origin, but Not Phylogeny, Drive Species Ecophysiological Response to Projected Climate

Knowledge of the relationship between environmental conditions and species traits is an important prerequisite for understanding determinants of community composition and predicting species response to novel climatic conditions. Despite increasing number of studies on this topic, our knowledge on importance of genetic differentiation, plasticity and their interactions along larger sets of species is still limited especially for traits related to plant ecophysiology. We studied variation in traits related to growth, leaf chemistry, contents of photosynthetic pigments and activity of antioxidative enzymes, stomata morphology and photosynthetic activity across eight Impatiens species growing along altitudinal gradients in Himalayas cultivated in three different temperature regimes and explored effects of among species phylogenetic relationships on the results. Original and target climatic conditions determine trait values in our system. The traits are either highly plastic (e.g., APX, CAT, plant size, neoxanthin, β-carotene, chlorophyll a/b, DEPSC) or are highly differentiated among populations (stomata density, lutein production). Many traits show strong among population differentiation in degree of plasticity and direction in response to environmental changes. Most traits indicate that the species will profit from the expected warming. This suggests that different processes determine the values of the different traits and separating the importance of genetic differentiation and plasticity is crucial for our ability to predict species response to future climate changes. The results also indicate that evolution of the traits is not phylogenetically constrained but including phylogenetic information into the analysis may improve our understanding of the trait-environment relationships as was apparent from the analysis of SLA.

Seasonal ionomic and metabolic changes in Aleppo pines growing on mine tailings under Mediterranean semi-arid climate

Aleppo pine is the most abundant conifer species in Mediterranean basin. Knowledge of adaptive mechanisms to cope with different environmental stresses simultaneously is necessary to improve its resilience to the predicted climatic changes and anthropogenic stressors, such as heavy metal/metal(loid)s (HMMs) pollution. Here, one year-old needles and rhizosphere soil samples from five mining and non-mining (NM) populations of Aleppo pines grown spontaneously in SE Spain were sampled in two consecutive years during spring and summer. Quantitative determination of a wide suite of edaphic, biochemical, and physiological parameters was performed, including soil physicochemical properties, ionome profile, foliar redox components, primary and secondary metabolites. Mining rhizosphere soils were characterized by elevated contents of HMMs, particularly lead and zinc, and low carbon, nitrogen and potassium levels. Multivariate data analysis based on needle ionome and antioxidative/oxidative parameters revealed a clear distinction between seasons irrespective of the population considered. Spring needles were characterized by higher levels of HMMs, sulfur, glutathione (GSH), proanthocyanidins (PAs), and soluble phenols (TPC), whereas reduced chlorophylls and increased levels of carotenoids, relative water content and K⁺, Na⁺ and Cl^- typified summer needles. In general mining populations had higher levels of ascorbate, and TPC, and exhibited higher antioxidant activities than the NM population. This could contribute to prevent oxidative injury induced by HMMs. Taken together, results suggest that seasonal factors have a more marked effect on the metabolism of the Aleppo pine populations studied than that exerted by soil conditions. This effect could be mediated by water availability in surface soil layers. If this conclusion is right, predicted rainfall reduction and temperature increase in the Mediterranean basin associated to global climate change would lead to pine needle metabolism to express the summer pattern for more prolonged periods. This, in turn, could negatively affect the performance of Aleppo pine populations.

Coordinated role of soluble and cell wall bound phenols is a key feature of the metabolic adjustment in a mining woody fleabane (Dittrichia viscosa L.) population under semi-arid conditions

Environmental contamination by hazardous heavy metals/metalloids (metal(loid)s) is growing worldwide. To restrict the migration of toxic contaminants, the establishment of a self-sustainable plant cover is required. Plant growth in multi-polluted soils is a challenging issue not only by metal(loid) toxicities, but also by the co-occurrence of other stressors. Dittrichia viscosa is a pioneer Mediterranean species able to thrive in metal(loid)-enriched tailings in semi-arid areas. The aim of the present work was to examine the metabolic adjustments involved in the acclimation responses of this plant to conditions prevailing in mine-tailings during Mediterranean spring and summer. For this purpose, fully-expanded leaves, and rhizosphere soil of both mining and non-mining populations of D. viscosa grown spontaneously in south-eastern Spain were sampled in two consecutive years. Quantitative analysis of >50 biochemical, physiological and edaphic parameters were performed, including nutrient status, metal(loid) contents, leaf redox components, primary and secondary metabolites, salicylic acid levels, and soil physicochemical properties. Results showed that mining plants exhibited high foliar Zn/Pb co-accumulation capacity, without substantially affecting their photosynthetic metabolism or nutritional status even in the driest summer period. The comparison of the antioxidative/oxidative profile between mining and non-mining D. viscosa populations revealed no major seasonal changes in the content of primary antioxidants (ascorbate and GSH), or in the levels of ROS. Multivariate analysis showed that phenylalanine ammonia-lyase (PAL) and peroxidase (PRX) activities and soluble and cell wall-bound phenols were potential biomarkers for discriminating between both populations. During the dry season, a marked enhancement in the activity of both PAL and soluble PRX resulted in both a drop in the accumulation of soluble phenols and an increase of the strong metal chelator caffeic acid in the cell-wall fraction, supporting the view that the plasticity of phenylpropanoid metabolism provide an effective way to counteract the effects of stress combinations.

PtrA/NINV, an alkaline/neutral invertase gene of Poncirus trifoliata, confers enhanced tolerance to multiple abiotic stresses by modulating ROS levels and maintaining photosynthetic efficiency

BACKGROUND

Alkaline/neutral invertase (A/N-INV), an enzyme that hydrolyzes sucrose irreversibly into glucose and fructose, is essential for normal plant growth,development, and stress tolerance. However, the physiological and/or molecular mechanism underpinning the role of A/N-INV in abiotic stress tolerance is poorly understood.

RESULTS

In this report, an A/N-INV gene (PtrA/NINV) was isolated from Poncirus trifoliata, a cold-hardy relative of citrus, and functionally characterized. PtrA/NINV expression levels were induced by cold, salt, dehydration, sucrose, and ABA, but decreased by glucose. PtrA/NINV was found to localize in both chloroplasts and mitochondria. Overexpression of PtrA/NINV conferred enhanced tolerance to multiple stresses, including cold, high salinity, and drought, as supported by lower levels of reactive oxygen species (ROS), reduced oxidative damages, decreased water loss rate, and increased photosynthesis efficiency, relative to wild-type (WT). The transgenic plants exhibited higher A/N-INV activity and greater reducing sugar content under normal and stress conditions.

CONCLUSIONS

PtrA/NINV is an important gene implicated in sucrose decomposition, and plays a positive role in abiotic stress tolerance by promoting osmotic adjustment, ROS detoxification and photosynthesis efficiency. Thus, PtrA/NINV has great potential to be used in transgenic breeding for improvement of stress tolerance.