Physiological response of Cu and Cu mine tailing remediation of Paulownia fortunei (Seem) Hemsl

Spatiotemporal variation of vegetation cover in mining areas of Dexing City, China

Dexing City is an important mining city in China, abounding in copper ore, lead ore, zinc ore, and other metal resources, and there are two large open-pit mines in its territory, Dexing Copper Mine and Yinshan Mine. The two open-pit mines have been expanding their mining production scale since 2005, with frequent mining activities; and the expansion of the pits and the discharge of solid waste will undoubtedly increase the land use and cause the destruction of vegetation. Therefore, we plan to visualize the change in vegetation cover in Dexing City from 2005 to 2020 and the expansion of the two open-pit mines by calculating changes of the Fractional Vegetation Cover (FVC) in the mining area using remote sensing technology. In this study, we calculated the FVC of Dexing City in 2005, 2010, 2015 and 2020 using data from NASA Landsat Database via ENVI image analysis software, plotted the FVC reclassified maps via ArcGIS, and conducted field investigations in the mining areas of Dexing City. In this way, we can visualize the spatial and temporal changes of vegetation cover in Dexing City from 2005 to 2020, and appreciate the situation of mining expansion and its solid waste discharge in Dexing City. The results of this study showed that the vegetation cover of Dexing City remained stable from 2005 to 2020, as the expansion of mining scale and mine pits was accompanied by active environmental management and land reclamation, setting a positive example for other mining cities.

Copper stress-induced phytotoxicity associated with photosynthetic characteristics and lignin metabolism in wheat seedlings

Copper (Cu) pollution is one of environmental problems that adversely affects the growth and development of plants. However, knowledge of lignin metabolism associated with Cu-induced phytotoxicity mechanism is insufficient. The objective of this study was to reveal the mechanisms underlying Cu-induced phytotoxicity by evaluating changes in the photosynthetic characteristics and lignin metabolism in the seedlings of wheat cultivar 'Longchun 30'. Treatment with varying concentrations of Cu clearly retarded seedling growth, as demonstrated by a reduction in the growth parameters. Cu exposure reduced the photosynthetic pigment content, gas exchange parameters, and chlorophyll fluorescence parameters, including the maximum photosynthetic efficiency, potential efficiency of photosystem II (PS II), photochemical efficiency of PS II in light, photochemical quenching, actual photochemical efficiency, quantum yield of PS II electron transport, and electron transport rate, but notably increased the nonphotochemical quenching and quantum yield of regulatory energy dissipation. Additionally, a significant increase was observed in the amount of cell wall lignin in wheat leaves and roots under Cu exposure. This increase was positively associated with the up-regulation of enzymes related to lignin synthesis, such as phenylalanine ammonia-lyase, 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, laccase, cell wall bound (CW-bound) guaiacol peroxidase, and CW-bound conifer alcohol peroxidase, and TaPAL, Ta4CL, TaCAD, and TaLAC expression. Correlation analysis revealed that lignin levels in the cell wall were negatively correlated with the growth of wheat leaves and roots. Taken together, Cu exposure inhibited photosynthesis in wheat seedlings, resulting from a reduction in photosynthetic pigment content, light energy conversion, and photosynthetic electron transport in the leaves of Cu-stressed seedlings, and the Cu-inhibitory effect on seedling growth was related to the inhibition of photosynthesis and an increase in cell wall lignification.

Ammonium regulates redox homeostasis and photosynthetic ability to mitigate copper toxicity in wheat seedlings

As an essential plant micronutrient, copper (Cu) is required as a component of several enzymes, but it can be highly toxic to plants when present in excess quantities. Nitrogen (N) application can help to alleviate the phytotoxic effects of heavy metals, including Cu, and different N forms significantly affect the uptake and accumulation of heavy metals in plants. The aim of this study was to determine the effects of different N forms, i.e., ammonium (NH₄⁺) and nitrate (NO₃^-), on Cu detoxification in wheat seedlings. The inhibition of seedling growth under excess Cu was more obvious in wheat plants supplied with NO₃^- than in those supplied with NH₄⁺. This growth inhibition was directly induced by excess Cu accumulation and reduced absorption of other mineral nutrients by the plants. Compared with seedlings treated with NO₃^-, those treated with NH₄⁺ showed a decrease in Cu-induced toxicity as a result of increased antioxidant capacity in the leaves and a lower redox potential in the rhizosphere. Furthermore, treatment with NH₄⁺ decreased the loss of mineral nutrients in wheat seedlings exposed to excess Cu. In conclusion, compared with supplying NO₃^-, supplying NH₄⁺ to wheat seedlings under Cu stress improved their ability to maintain their nutritional and redox balance and increased their antioxidant capacity, thereby preventing a decline in photosynthesis. According to our results, NH₄⁺ is more effective than NO₃^- in reducing Cu phytotoxicity in wheat seedlings.

The Possibility of Using Paulownia elongata S. Y. Hu × Paulownia fortunei Hybrid for Phytoextraction of Toxic Elements from Post-Industrial Wastes with Biochar

The potential of the Paulownia hybrid for the uptake and transport of 67 elements along with the physiological response of plants cultivated in highly contaminated post-industrial wastes (flotation tailings—FT, and mining sludge—MS) was investigated. Biochar (BR) was added to substrates to limit metal mobility and facilitate plant survival. Paulownia could effectively uptake and translocate B, Ca, K, P, Rb, Re and Ta. Despite severe growth retardation, chlorophyll biosynthesis was not depleted, while an increased carotenoid content was noted for plants cultivated in waste materials. In Paulownia leaves and roots hydroxybenzoic acids (C6-C1) were dominant phenolics, and hydroxycinnamic acids/phenylpropanoids (C6-C3) and flavonoids (C6-C3-C6) were also detected. Plant cultivation in wastes resulted in quantitative changes in the phenolic fraction, and a significant drop or total inhibition of particular phenolics. Cultivation in waste materials resulted in increased biosynthesis of malic and succinic acids in the roots of FT-cultivated plants, and malic and acetic acids in the case of MS/BR substrate. The obtained results indicate that the addition of biochar can support the adaptation of Paulownia seedlings growing on MS, however, in order to limit unfavorable changes in the plant, an optimal addition of waste is necessary.

Physiological responses and metal distributions of different organs of Phragmites australis shoots under acid mine drainage stress

Phragmites australis, which is widely distributed throughout the world, is often used in the phytoremediation of acid mine drainage (AMD) due to its various mechanisms for survival under extremely harsh conditions. To explore the different responses of different aerial organs of P. australis to stress, soil and plant samples were collected from the AMD-polluted area of the Tongling mining area. The contents of manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), and lead (Pb) in the soil and the leaf blades, leaf sheaths, and stems of P. australis as well as the contents/activities of cysteine synthase (CSase), superoxide dismutase (SOD), peroxidase (POD), glutathione (GSH), malondialdehyde (MDA), and proline (Pro) in the organs were determined. Our results revealed that the leaf sheath had the highest potential to store metals of all the organs. The highest translocation factor (TF) for Fe was observed from the stems to the leaf sheaths. A higher bioconcentration factor (BCF) for Mn was found in the leaf blades and leaf sheaths, while higher BCFs for Cd and Zn were observed in the stems. The content/activity of enzymatic and non-enzymatic stress-resistance substances varied from organ to organ. In general, the leaf sheaths remained almost as or slightly less stress-resistant than the leaf blades. It can be concluded that different plant organs play different roles in stress resistance, and understanding the tolerance mechanism of leaf sheaths to metals is essential for the application of phytoremediation procedures.

Effect of citric acid and vermi-wash on growth and metal accumulation of Sorghum bicolor cultivated in lead and nickel contaminated soil

The aim of the present study is to assess the influence of vermi-wash (VW) and citric acid (CA) on Sorghum bicolor growth and phytoaccumulation of lead (Pb) and nickel (Ni) contaminated soil. The biomass of the S. bicolor has been enhanced by the addition of VW (24 and 26%) and CA (11 and 9%) in Pb and Ni contaminated soil, respectively. The VW treatment showed enhanced shoot and root lengths and chlorophyll concentrations compared to CA. The shoot anatomic structure showed an accumulation of Pb and Ni were positively impacted by the amendment of VW and CA. In addition, VW treatment showed enhanced antioxidant enzymes activity (140, 125 and 152 U/mg of CAT, SOD and POD). Further, the plants grown in Pb contaminated soil treated with VW showed enhanced Rubisco activity of 1.49 U/ml, whereas, CA treatment showed 1.23 U/ml of Rubisco. It has been observed that the VW showed as a potential chelator as well as plant beneficial formulation for the enhanced phyto-remediation of Pb and Ni.

Appraising growth, oxidative stress and copper phytoextraction potential of flax (Linum usitatissimum L.) grown in soil differentially spiked with copper

Flax (Linum usitatissimum L.) is one of the oldest predominant industrial crops grown for seed, oil and fiber. The present study was executed to evaluate the morpho-physiological traits, biochemical responses, gas exchange parameters and phytoextraction potential of flax raised in differentially copper (Cu) spiked soil viz (0, 200, 400 and 600 mg Cu kg^-1 soil) under greenhouse pot experiment. The results revealed that flax plants were able to grow up to 400 mg kg^-1 Cu level without showing significant growth inhabitation while, further inference of Cu (600 mg kg^-1) in the soil prominently inhibited flax growth and biomass accumulation. Compared to the control, contents of proline and malondialdehyde (MDA) were increased by 160.0% and 754.1% accordingly, at 600 mg Cu kg^-1 soil level. The Cu-induced oxidative stress was minimized by the enhanced activities of superoxide dismutase (SOD) by 189.2% and guaiacol peroxidase (POD) by 300.8% in the leaves of flax at 600 mg Cu kg^-1 soil level, compared to the untreated control. The plant Cu concentration was determined at 35, 70, 105 and 140 days after sowing (DAS) and results depicted that 16.9 times higher Cu concentration was accumulated in flax roots while little (14.9 times) was transported to the shoots at early stage of growth, i.e. 35 DAS. While at 140 DAS, Cu was highly (21.7 times) transported to the shoots while, only 12.3 times Cu was accumulated in the roots at 600 mg Cu kg^-1 soil level, compared to control. Meanwhile, Cu uptake by flax was boosted up to 253 mg kg^-1 from the soil and thereby extracted 43%, 39% and 41% of Cu at 200, 400 and 600 mg Cu kg^-1 soil level, compared to initial Cu concentration. Therefore, study concluded that flax has a great potential to accumulate high concentration of Cu in its shoots and can be utilized as phytoremediation material when grown in Cu contaminated soils.

ceRNA Cross-Talk in Paulownia Witches' Broom Disease

Long noncoding RNA (lncRNA), circular RNA (circRNA), and microRNA (miRNA) are important in the regulation of life activities. However, their function is unclear in Paulownia fortunei. To identify lncRNAs, circRNAs, and miRNA, and investigate their roles in the infection progress of Paulownia witches’ broom (PaWB) disease, we performed RNA sequencing of healthy and infected P. fortunei. A total of 3126 lncRNAs, 1634 circRNAs, and 550 miRNAs were identified. Among them, 229 lncRNAs, 65 circRNAs, and 65 miRNAs were differentially expressed in a significant manner. We constructed a competing endogenous RNA (ceRNA) network, which contains 5 miRNAs, 4 circRNAs, 5 lncRNAs, and 15 mRNAs, all of which were differentially expressed between healthy and infected P. fortunei. This study provides the first catalog of candidate ceRNAs in Paulownia and gives a revealing insight into the molecular mechanism responsible for PaWB.

Implications of polyploidy events on the phenotype, microstructure, and proteome of Paulownia australis

Polyploidy events are believed to be responsible for increasing the size of plant organs and enhancing tolerance to environmental stresses. Autotetraploid Paulownia australis plants exhibit superior traits compared with their diploid progenitors. Although some transcriptomics studies have been performed and some relevant genes have been revealed, the molecular and biological mechanisms regulating the predominant characteristics and the effects of polyploidy events on P. australis remain unknown. In this study, we compared the phenotypes, microstructures, and proteomes of autotetraploid and diploid P. australis plants. Compared with the diploid plant, the leaves of the autotetraploid plant were longer and wider, and the upper epidermis, lower epidermis, and palisade layer of the leaves were thicker, the leaf spongy parenchyma layer was thinner, the leaf cell size was bigger, and cell number was lower. In the proteome analysis, 3,010 proteins were identified and quantified, including 773 differentially abundant proteins. These results may help to characterize the P. australis proteome profile. Differentially abundant proteins related to cell division, glutathione metabolism, and the synthesis of cellulose, chlorophyll, and lignin were more abundant in the autotetraploid plants. These results will help to enhance the understanding of variations caused by polyploidy events in P. australis. The quantitative real-time PCR results provided details regarding the expression patterns of the proteins at mRNA level. We observed a limited correlation between transcript and protein levels. These observations may help to clarify the molecular basis for the predominant autotetraploid characteristics and be useful for plant breeding in the future.

Effects of organic acids on the photosynthetic and antioxidant properties and accumulations of heavy metals of Melilotus officinalis grown in Cu tailing

The effect of citric acid (CA), acetic acid (Ac), and ethylene diamine tetraacetic acid (EDTA) on the photosynthetic and antioxidant properties and the accumulation of some heavy metals (HMs) of Melilotus officinalis seedling growing in Cu mine tailings for 25 days were studied. Results showed that the formation of photosynthesizing cells of M. officinalis was inhibited by EDTA at 2 mmol/kg. Photosynthetic pigment contents under EDTA of 2 mmol/kg were reduced by 26, 40, and 19 %, respectively, compared to the control. The proline contents in aboveground and underground parts increased as the level of EDTA was enhanced. CA and Ac enhanced the activities of superoxide dismutase (SOD) and peroxidase (POD) in the aboveground parts and EDTA inhibited the activity of POD in the underground parts. The addition of CA promoted significantly the growth of M. officinalis, while the biomass decreased significantly under 2 mmol/kg EDTA. Cu contents in the aboveground parts treated with 0.5 and 2.0 mmol/kg EDTA reached 175.50 and 265.17 μg/g dry weight, respectively. Ac and EDTA treatments promoted Cd to translocate from root to aboveground parts. The result indicated that M. officinalis was a tolerant species of Cu tailing and can be used to remediate Cu contaminated environment, and rationally utilization of organic acids, especially EDTA, in the phytoremediation can improve the growth and metals accumulation of M. officinalis.

Pb uptake and toxicity to Iris halophila tested on Pb mine tailing materials

Pb tolerant mechanisms, plant physiological response and Pb sub-cellular localization in the root cells of Iris halophila were studied in sand culture and the Pb mine tailings. Results showed that the activities of superoxide dismutase (SOD) and peroxidase (POD) in the underground parts and the activity of catalase (CAT) in the aboveground and underground parts increased as Pb level was enhanced. Glutathione (GSH) and ascorbic acid (AsA) contents increased by Pb treatments. Pb deposits were found in the middle cell walls or along the inner side of epibiotic protoplasm of some cells which accumulated a large quantity of Pb and died. The dry weights (DWs) of aboveground parts under all Pb tailings treatments decreased insignificantly, while the DW of the underground parts growing in the pure Pb tailings decreased significantly. Pb, Cu, Cd, and Zn contents increased significantly as the levels of Pb tailings were enhanced and Pb contents in the aboveground and underground parts reached 64.75 and 751.75 μg/g DW, respectively, at pure Pb tailings treatment. The results indicated that I. halophila is a promising plant in the phytoremediation of Pb contaminated environment. Some antioxidant enzymes, antioxidants and compartmentalization of Pb were played major roles in Pb tolerance of I. halophila.

An evaluation of EDTA additions for improving the phytoremediation efficiency of different plants under various cultivation systems

Previous studies have shown that phytoremediation usually requires soil amendments, such as chelates, to mobilize low bioavailability heavy metals for better plant absorption and, consequently, for remediation efficiency. A total dry biomass of 3.39 and 0.0138 kg per plant was produced by a phytoremediator, Eucalyptus globulus, and a nitrogen fixing crop, Cicer arietinum (chickpea), respectively. The accumulation of Pb in E. globulus and chickpea reached 1170.61 and 1.33 mg per plant (700 and 324 mg kg(-1)), respectively, under an ethylene diamine tetraacetic acid (EDTA) treatment, which was a five and sixfold increase over the value in untreated experiments, respectively. EDTA enhanced the phytoremediation efficiency and increased the heavy metal concentration in the soil solution. In pot experiments, approximately 27 % of the initial Pb leached from the spiked soil after EDTA and 25 mm artificial precipitation additions into soil without plants, which was considerably larger than the value under the same conditions without EDTA application (7 %). E. globulus planted in a mixed culture had higher water use efficiency than monocultures of either species in field experiments, and E. globulus intercepted almost all of the artificial precipitation in the pot experiments. This study demonstrates that E. globulus can maximize the potential of EDTA for improving the phytoremediation efficiency and minimizing its negative effects to the environment simultaneously by absorbing the metal-rich leachate, especially in a mixed culture of E. globulus and chickpeas.

Three-year study of fast-growing trees in degraded soils amended with composts: Effects on soil fertility and productivity

Currently, worries about the effects of intensive plantations on long-term nutrient supply and a loss of productivity have risen. In this study two composts were added to degraded soils where this type of intensive crops were growing, to avoid the soil fertility decrease and try to increase biomass production. For the experiment, two degraded soils in terms of low organic carbon content and low pH were selected in South-West Spain: La Rábida (RA) and Villablanca (VI) sites. Both study sites were divided into 24 plots. In RA, half of the plots were planted with Populus x canadensis "I-214"; the other half was planted with Eucalyptus globulus. At the VI site, half of the plots were planted with Paulownia fortunei, and the other plots were planted with Eucalyptus globulus. For each tree and site, three treatments were established (two organic composts and a control without compost), with four replications per treatment. The organic amendments were "alperujo" compost, AC, a solid by-product from the extraction of olive oil, and BC, biosolid compost. During the three years of experimentation, samples of soils and plants were analyzed for studying chemical and biochemical properties of soil, plant growth and plant nutritional status and biomass production. The composts increased total organic carbon, water-soluble carbon, nutrients and pH of soil only in the most acidic soil. Soil biochemical quality was calculated with the geometric mean of the enzymatic activities (Dehydrogenase, β-glucosidase, Phosphatase and Urease activities) determined in soils. The results showed a beneficial improvement in comparison with soils without compost. However, the best results were found in the growth and biomass production of the studied trees, especially in Eucalyptus. Nutritional levels of leaves of the trees were, in general, in the normal established range for each species, although no clear effect of the composts was observed. The results of this study justify the addition of compost to guarantee good biomass production and maintain or improve soil management in degraded soils, especially in acid soils.

Improving sustainability in the remediation of contaminated soils by the use of compost and energy valorization by Paulownia fortunei

The plantation of fast growing trees in contaminated sites, in combination with the use of organic wastes, could partially solve a dual environmental problem: the disposal of these wastes and the improvement of soil quality in these degraded soils. This study evaluated the effects of two compost on the quantity and quality of Paulownia fortunei biomass and on syngas production by biomass gasification, produced by plants growing on trace elements contaminated soils. Compost increased biomass production to values similar to those produced in non-contaminated soils, due to the improvement in plant nutritional status. Moreover, biomass quality for gasification was increased by compost addition. Trace element accumulation in the biomass was relatively low and not related to biomass production or the gas quality obtained through gasification. Thus, P. fortunei plantations could pose an opportunity to improve the economic balance of the revegetation of contaminated soils, given that other commercial uses such as food or fodder crop production is not recommended in these soils.

Copper induced oxidative stresses, antioxidant responses and phytoremediation potential of Moso bamboo (Phyllostachys pubescens)

Moso bamboo is recognized as phytoremediation plant due to production of huge biomass and high tolerance in stressed environment. Hydroponics and pot experiments were conducted to investigate mechanism of copper tolerance and to evaluate copper accumulation capacity of Moso bamboo. In hydroponics experiment there was non significant variation in MDA contents of leaves compared with control. SOD and POD initially indicated enhancing trend with application of 5 μM Cu and then decreased consistently with application of 25 and 100 μM Cu. Application of each additional increment of copper have constantly enhanced proline contents while maximum increase of proline was observed with application of 100 μM copper. In pot experiment chlorophyll and biomass initially showed increasing tendency and decreased gradually with application of each additional increment of Cu. Normal growth of Moso bamboo was observed with application of 100 mg kg⁻¹ copper. However, additional application of 300 or 600 mg kg⁻¹ copper had significantly inhibited growth of Moso bamboo. The concentration of Cu in Moso bamboo has attained the levels of 340, 60, 23 mg kg⁻¹ in roots, stems and leaves respectively. The vacuoles were the main organs which accumulated copper and reduced toxicity of copper as studied by TEM-DEX technology.

Identification of genes related to the phenotypic variations of a synthesized Paulownia (Paulownia tomentosa×Paulownia fortunei) autotetraploid

Paulownia is a fast-growing deciduous tree native to China. It has great economic importance for the pulp and paper industries, as well as ecological prominence in forest ecosystems. Paulownia is of much interest to plant breeder keen to explore new plant varieties by selecting on the basis of phenotype. A newly synthesized autotetraploid Paulownia exhibited advanced characteristics, such as greater yield, and higher resistance than the diploid tree. However, tissue-specific transcriptome and genomic data in public databases are not sufficient to understand the molecular mechanisms associated with genome duplication. To evaluate the effects of genome duplication on the phenotypic variations in Paulownia tomentosa×Paulownia fortunei, the transcriptomes of the autotetraploid and diploid Paulownia were compared. Using Illumina sequencing technology, a total of 82,934 All-unigenes with a mean length of 1109 bp were assembled. The data revealed numerous differences in gene expression between the two transcriptomes, including 718 up-regulated and 667 down-regulated differentially expressed genes between the two Paulownia trees. An analysis of the pathway and gene annotations revealed that genes involved in nucleotide sugar metabolism in plant cell walls were down-regulated, and genes involved in the light signal pathway and the biosynthesis of structural polymers were up-regulated in autotetraploid Paulownia. The differentially expressed genes may contribute to the observed phenotypic variations between diploid and autotetraploid Paulownia. These results provide a significant resource for understanding the variations in Paulownia polyploidization and will benefit future breeding work.

Quality of trace element contaminated soils amended with compost under fast growing tree Paulownia fortunei plantation

The use of fast growing trees could be an alternative in trace element contaminated soils to stabilize these elements and improve soil quality. In this study we investigate the effect of Paulownia fortunei growth on trace element contaminated soils amended with two organic composts under semi-field conditions for a period of 18 months. The experiment was carried out in containers filled with tree different soils, two contaminated soils (neutral AZ and acid V) and a non contaminated soil, NC. Three treatments per soil were established: two organic amendments (alperujo compost, AC, and biosolid compost, BC) and a control without amendment addition. We study parameters related with fertility and contamination in soils and plants. Paulownia growth and amendments increased pH in acid soils whereas no effect of these factors was observed in neutral soils. The plant and the amendments also increased organic matter and consequently, soil fertility. Positive results were also found in soils that were only affected by plant growth (without amendment). A general improvement of "soil biochemical quality" was detected over time and treatments, confirming the positive effect of amendments plus paulownia. Even in contaminated soils, except for Cu and Zn, trace element concentrations in leaves were in the normal range for plants. Results of this mid-term study showed that Paulownia fortunei is a promising species for phytoremediation of trace element polluted soils.

Evidence of population genetic effects in Peromyscus melanophrys chronically exposed to mine tailings in Morelos, Mexico

Effects of environmental chemical pollution can be observed at all levels of biological organization. At the population level, genetic structure and diversity may be affected by exposure to metal contamination. This study was conducted in Huautla, Morelos, Mexico in a mining district where the main contaminants are lead and arsenic. Peromyscus melanophrys is a small mammal species that inhabits Huautla mine tailings and has been considered as a sentinel species. Metal bioaccumulation levels were examined by inductively coupled plasma mass spectrometry and genetic analyses were performed using eight microsatellite loci in 100 P. melanophrys individuals from 3 mine tailings and 2 control sites. The effect of metal bioaccumulation levels on genetic parameters (population and individual genetic diversity, genetic structure) was analyzed. We found a tissue concentration gradient for each metal and for the bioaccumulation index. The highest values of genetic differentiation (Fst and Rst) and the lowest number of migrants per generation (Nm) were registered among the exposed populations. Genetic distance analyses showed that the most polluted population was the most genetically distant among the five populations examined. Moreover, a negative and significant relationship was detected between genetic diversity (expected heterozygosity and internal relatedness) and each metal concentration and for the bioaccumulation index in P. melanophrys. This study highlights that metal stress is a major factor affecting the distribution and genetic diversity levels of P. melanophrys populations living inside mine tailings. We suggest the use of genetic population changes at micro-geographical scales as a population level biomarker.

Organic acids on the growth, anatomical structure, biochemical parameters and heavy metal accumulation of Iris lactea var. chinensis seedling growing in Pb mine tailings

The effect of citric acid (CA) and ethylene diamine tetraacetic acid (EDTA) on the growth, anatomical structure, physiological responses and lead (Pb) accumulation of Iris lactea var. chinensis seedling growing in Pb mine tailings for 30 days were studied. Results showed that the dry weights (DW) of roots decreased significantly under both levels of CA. The DWs of leaves and roots treated with 2 mmol/kg EDTA decreased significantly and were 23 and 54 %, respectively, lower than those of the control. The tolerant indexes of I. lactea var. chinensis under all treatments of organic acids were lower than control. The root tip anatomical structure was little affected under the treatments of 2 mmol/kg CA and 2 mmol/kg EDTA compared with control. However, the formation of photosynthesizing cells was inhibited by the treatment of 2 mmol/kg EDTA. The concentrations of chlorophyll a, chlorophyll b and total carotenoids in the leaves treated with 2 mmol/kg EDTA significantly decreased. Higher CA level and lower EDTA level could trigger the synthesis of ascorbic acid and higher level of EDTA could trigger the synthesis of glutathione. CA and EDTA could promote Pb accumulation of I. lactea var. chinensis and Pb concentration in the leaves and roots at 2 mmol/kg EDTA treatment increased significantly and reached to 160.44 and 936.08 μg/g DW, respectively, and 1.8 and 1.6 times higher than those of the control. The results indicated that I. lactea var. chinensis could be used to remediate Pb tailing and the role of EDTA in promoting Pb accumulation was better than CA did.

Salicylic acid alleviates copper toxicity in rice (Oryza sativa L.) seedlings by up-regulating antioxidative and glyoxalase systems

The present study investigated the effect of salicylic acid (SA) on toxic symptoms, lipid peroxidation, reactive oxygen species generation and responses of antioxidative and glyoxalase systems in rice seedlings grown hydroponically under copper (Cu) stress for 48 h. Exposures of 75 and 150 μM Cu(2+) caused toxicity symptoms (chlorosis, necrosis and rolling in leaves), sharp increases in malondialdehyde (MDA), hydrogen peroxide (H2O2) contents and lipoxygenase (LOX) activity with concomitant reductions of chlorophyll (Chl) and relative water content (RWC). Both levels of Cu decreased ascorbic acid (AsA), glutathione (GSH), non-protein thiol (NPT) and proline contents in roots but rather increased in leaves except that AsA decreased in leaves too. These results together with overaccumulation of superoxide (O 2 (•-) ) and H2O2 in leaves revealed that Cu exposures induced oxidative stress. Contrary, SA-pretreatment (100 μM for 24 h) reduced toxicity symptoms and diminished Cu-induced increases in LOX activity, H2O2, MDA and proline contents while the levels of RWC, Chl, AsA and redox ratios were elevated. Higher levels of GSH and NPT were also observed in roots of SA-pretreated Cu-exposed seedlings. SA-pretreatment also exerted its beneficial role by inhibiting the Cu upward process. Studies on antioxidant enzymes showed that SA further enhanced the activities of superoxide dismutase, ascorbate peroxidase, glutathione reductase and glutathione peroxidase, and also elevated the depressed activities of catalase, dehydroascorbate reductase and glutathione S-transferase particularly at 150 μM Cu(2+) stress. In addition, the activity of glyoxalase system (glyoxalase I and II) was further elevated by SA pretreatment in the Cu-exposed seedlings. These results concluded that SA-mediated retention of Cu in roots and enhanced capacity of both antioxidative and glyoxalase systems might be associated with the alleviation of Cu-toxicity in rice seedlings.