Tolerance and accumulation of lead by species of Iris L

Phytostabilization of metal(loid)s by ten emergent macrophytes following a 90-day exposure to industrially contaminated groundwater

Better understanding of macrophyte tolerance under long exposure times in real environmental matrices is crucial for phytoremediation and phytoattenuation strategies for aquatic systems. The metal(loid) attenuation ability of 10 emergent macrophyte species (Carex riparia, Cyperus longus, Cyperus rotundus, Iris pseudacorus, Juncus effusus, Lythrum salicaria, Menta aquatica, Phragmites australis, Scirpus holoschoenus, and Typha angustifolia) was investigated using real groundwater from an industrial site, over a 90-day exposure period. A "phytobial" treatment was included, with 3 plant growth-promoting rhizobacterial strains. Plants exposed to the polluted water generally showed similar or reduced aerial biomass compared to the controls, except for C. riparia. This species, along with M. aquatica, exhibited improved biomass after bioaugmentation. Phytoremediation mechanisms accounted for more than 60% of As, Cd, Cu, Ni, and Pb removal, whilst abiotic mechanisms contributed to ∼80% removal of Fe and Zn. Concentrations of metal(loid)s in the roots were generally between 10-100 times higher than in the aerial parts. The macrophytes in this work can be considered "underground attenuators", more appropriate for rhizostabilization strategies, especially L. salicaria, M. aquatica, S. holoschoenus, and T. angustifolia. For I. pseudacorus, C. longus, and C. riparia; harvesting the aerial parts could be a complementary phytoextraction approach to further remove Pb and Zn. Of all the plants, S. holoschoenus showed the best balance between biomass production and uptake of multiple metal(loid)s. Results also suggest that multiple phytostrategies may be possible for the same plant depending on the final remedial aim. Phytobial approaches need to be further assessed for each macrophyte species.

Removal of heavy metals using Iris species: A potential approach for reclamation of heavy metal-polluted sites and environmental beautification

Globally, the number of heavy metal (HM)-polluted sites has increased rapidly in recent years, posing a serious threat to agricultural productivity, human health, and environmental safety. Hence, it is necessary to remediate HM-polluted sites to increase cultivatable lands for agricultural productivity, prevent hazardous effects to human health, and promote environmental safety. Removal of HMs using plants (phytoremediation) is a promising method as it is eco-friendly. Recently, ornamental plants have been widely used in phytoremediation programs as they can simultaneously eliminate HMs and are aesthetically pleasing. Among the ornamental plants, Iris species are frequently used; however, their role in HM remediation has not been reviewed yet. Here, the importance of Iris species in the ornamental industry and their different commercial aspects are briefly described. Additionally, the mechanisms of how the plant species absorb and transport the HMs to the above-ground tissues and tolerate HM stress are highlighted. The variation in HM remediation efficiency depending on the plant species, HM type and concentration, use of certain supplements, and experimental conditions are also discussed. Iris species are able to remove other hazards as well, such as pesticides, pharmaceutical compounds, and industrial wastes, from polluted soils or waste-water. Owing to the valuable information presented in this review, we expect more applications of the species in reclaiming polluted sites and beautifying the environment.

IlAP2, an AP2/ERF Superfamily Gene, Mediates Cadmium Tolerance by Interacting with IlMT2a in Iris lactea var. chinensis

Cadmium (Cd) stress has a major impact on ecosystems, so it is important to find suitable Cd-tolerant plants while elucidating the responsible molecular mechanism for phytoremediation to manage Cd soil contamination. Iris lactea var. chinensis is an ornamental perennial groundcover plant with strong tolerance to Cd. Previous studies found that IlAP2, an AP2/ERF superfamily gene, may be an interacting partner of the metallothionein gene IlMT2a, which plays a key role in Cd tolerance. To study the role of IlAP2 in regulating Cd tolerance in I. lactea, we analyzed its regulation function and mechanism based on a yeast two-hybrid assay, a bimolecular fluorescence complementation test, quantitative real-time PCR, transgenics and transcriptome sequencing. The results showed that IlAP2 interacts with IlMT2a and may cooperate with other transcription factors to regulate genes involved in signal transduction and plant hormones, leading to reduced Cd toxicity by hindering Cd transport. These findings provide insights into the mechanism of IlAP2-mediated stress responses to Cd and important gene resources for improving plant stress tolerance in phytoremediation.

Genetic diversity and growth responses of Indonesian tomato (

Tomato (Solanum lycopersicum L.) is cultivated and consumed worldwide, including in Indonesia. It is used in the food, cosmetic, and pharmaceutical industries, due to its high content of carotenoid (lycopene) compounds that have antioxidant and anticancer activities. In Indonesia, although several cultivars of tomato are cultivated, including Opal, Permata, Mutiara, and Rewako, studies on their genetic information are limited. Unpredicted climate change as well as heavy metal contamination, especially Pb pollution, has threatened Indonesian food security. Therefore, our study aimed to analyze the genetic diversity of the four local tomatoes using random amplified polymorphic DNA (RAPD) markers and to determine the growth responses of several local tomato genotypes under Pb stress. In this study, morphological responses to Pb, including plant height and root length were observed. The RAPD analysis showed that Rewako and Permata were distinct, whereas Opal and Mutiara were closely related, possessing 81.8% similarity. Pb stress influenced plant height and root length in the four tomato genotypes, with each genotype exhibiting different morphological responses than others. However, the closely related Mutiara and Opal genotypes demonstrated similar responses to Pb stress to Permata and Rewako. Our study demonstrates that RAPD are sensitive and efficient for elucidating the genomic profile of the tomato genotypes. In addition, our results suggest that genetic variation among tomato genotypes might influence the morphological responses against Pb stress.

Effects of Herbaspirillum sp. p5-19 assisted with alien soil improvement on the phytoremediation of copper tailings by Vetiveria zizanioides L

Microbial assisted phytoremediation and reclamation are both potential contaminated soil remediation technologies, but little is known about the combined application of the two technologies on real contaminated soils. This study investigated the potential of Herbaspirillum sp. p5-19 (p5-19) assisted with alien soil improvement on improving stress tolerance and enhancing the accumulation of Mn, Cu, Zn, and Cd by Vetiveria zizanioides L. in copper tailings. Phytoremediation potential was evaluated by plant biomass and the ability of plants to absorb and transfer heavy metals. Results showed that the biomass was increased by 19.64-173.81% in p5-19 inoculation treatments with and without alien soil improvement compared with control. Meanwhile, photosynthetic pigment contents were enhanced in co-inoculation treatment (p5-19 with alien soil improvement). In addition, the malondialdehyde (MDA) content was decreased, and the activities of antioxidant enzymes such as ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased in p5-19 treatment, thereby alleviating the oxidative stress. Moreover, co-inoculation significantly (p < 0.05) increased the concentrations of Mn, Cu, Zn, and Cd in the roots and shoots of V. zizanioides. In particular, the highest concentrations of Mn, Zn, and Cd in the shoots (roots) were obtained in covering 10 cm combined with p5-19 inoculation treatment, which were 4.44- (2.71-), 4.73- (3.87-), and 5.93- (4.35-) fold as that of the controls, respectively. These results provided basis for the change of phytoremediation ability of V. zizanioides after inoculation. We concluded that p5-19 assisted with alien soil improvement was a potential strategy for enhancing phytoremediation ability in tailings.

Changes in electricity production and microbial community evolution in constructed wetland-microbial fuel cell exposed to wastewater containing Pb(II)

Two constructed wetland microbial fuel cell (CW-MFC) devices, experimental group (EG, with 5 mg/L Pb(II) addition) and control group (CG) were built to explore the changes in power generation, wastewater purification and microbial community structure under Pb(II) stress. The voltage of EG (343.16 ± 12.14 mV) was significantly higher (p < 0.01) than that of CG (295.49 ± 13.91 mV), and the highest power density of the EG and CG were 7.432 mW·m^-2 and 3.873 mW·m^-2, respectively. There was no significant difference in the removal of common pollutants between these groups except for the NH₄⁺-N removal efficiency, which was probably caused by the inhibition of the bioactivity of Comamonas (AOB) in the anode of the experimental group by Pb(II). Pb(II) was effectively removed by CW-MFC (84.86 ± 3%), and the abundant amount of fulvic acid-like matter in the extracellular polymeric substance (EPS) of the EG contributed to its removal. The presence of Pb(II) had a negative effect on both microbial community diversity and species richness. The abundance of a lead resistance gene, pbrT, decreased with long-term Pb(II) pressure. This is evidence of microbial adaptation to Pb(II).

Assessment of phytostabilization potential of two Salix L. clones based on the effects of heavy metals on the root anatomical traits

Willow species (Salix L.) are a useful tool for assessing phytostabilization of the sites polluted by heavy metals. Phytostabilization potential of two willow genotypes (Salix alba L. clone '68/53/1' and Salix nigra Marshall clone '0408') has been evaluated in a 45-day hydroponic experiment, using stem cuttings (diameter 12 to 14 mm, length 20 cm) exposed to two concentrations (10^-4 M and 10^-5 M) of individually applied Cd, Ni, and Pb. Metals were diluted in 25% Hoagland's solution, in forms of CdCl₂·H₂O, NiSO₄·6H₂O, and Pb-EDTA. The control group of cuttings was grown in 25% Hoagland's solution without heavy metals. High Cd concentrations in willow roots, 8637 mg/kg (clone '68/53/1') and 6728 mg/kg of dry weight (clone '0408'), have indicated a high phytostabilization potential. However, detailed analyses of cross-sectional area of the root cortex and the central cylinder revealed that the excess concentration of Cd led to a significant reduction of measured anatomical root's traits of clone '68/53/1' in comparison with the control samples. Excessive concentration of Ni and Pb in nutrient solution increased the values of quantitatively measured root's traits of clone '0408', implying stimulatory effects of the applied concentrations. Concentration of 10^-4 M of each metal had more negative effects on the roots' anatomical traits, notably on parenchymal and exodermal cells and vessels. Deposits of metals were observed in root tissues. Clone '0408' demonstrated an increased tolerance to heavy metals, which could potentially make this clone useful in phytostabilization.

Subcellular distribution and chemical forms of lead in the red algae, Porphyra yezoensis

The subcellular distribution and chemical forms of lead (Pb) were examined in the red algae, Porphyra yezoensis. The algae was exposed to three different Pb treatments (0.01, 0.1 and 1.0 mg L^-1) for up to 144 h. In the control groups, about 45% of Pb was localized in the cell wall, and 27.5% in the organelle and soluble fractions respectively. The dominant chemical forms of Pb was extracted by 80% ethanol (52.9%), while the form extracted by NaCl (1 M) was lowest. In the treatment groups, the cell wall and the organelle fraction were the main subcellular fractions for the 0.10 mg L^-1 and 1.0 mg L^-1 groups; while for the 0.01 mg L^-1 groups, Pb was approximately distributed in the cell wall, organelle and the soluble fractions. The dominant ethanol extractable form of Pb in the control and 0.01 mg L^-1 groups were replaced by less active 2% acetic acid (HAc) extractable form in the 0.1 and 1.0 mg L^-1 groups. Different from other terrestrial plants, the proportion of 1 M NaCl extractable form of the pectates and protein integrated Pb in P. yezoensis was lowest for both control and treatment groups. The strategy with deposition Pb in the cell wall and formation the precipitation of less active HAc extractable form maybe one of the mechanisms for accumulation, transportation and detoxification of Pb in P. yezoensis.

Exogenous glutathione increased lead uptake and accumulation in Iris lactea var. chinensis exposed to excess lead

Long- and short-term hydroponic experiments were conducted to study the effect of different concentrations of exogenous glutathione (GSH) on Pb uptake, translocation, and gene expresses in Iris lactea var. chinensis exposed to excess lead (Pb). Exogenous GSH remarkedly promoted Pb uptake and translocation in long-term (14 d) experiment, and the GSH-dose-dependent increases in shoot and root Pb contents existed obviously when GSH concentrations were lower than 800 mg·L^-1. The fresh weight in gradual rise in plants was observed with the increase of exogenous GSH concentration. In short-term (24 h) experiment, Pb contents in roots under Pb with _L-buthionine sulfoximine (BSO, a known inhibitor of GSH biosynthesis) treatments were significantly lower than that under Pb exposure alone. The transcript levels of three genes (Ilγ-ECS, IlGS, and IlPCS) involved in GSH synthesis and metabolism, showed no significant change in expression pattern except that upregulation after 24 h of treatment with Pb and GSH in comparison with that of the single Pb treatment. Further, the level of IlGS transcript after exposure for 4 h was much higher than that of Ilγ-ECS and IlPCS transcripts. All these results obtained here suggest that exogenous GSH can increase Pb accumulation, detoxification, and translocation to the shoot.

De novo characterization of the Iris lactea var. chinensis transcriptome and an analysis of genes under cadmium or lead exposure

Iris lactea var. chinensis (I. lactea var. chinensis) is tolerant to accumulations of cadmium (Cd) and lead (Pb). In this study, the transcriptome of I. lactea var. chinensis was investigated under Cd or Pb stresses. Using the gene ontology database, 31,974 unigenes were classified into biological process, cellular component and molecular function. In total, 13,132 unigenes were involved in enriched Encyclopedia of Genes and Genomes (KEGG) metabolic pathways, and the expression levels of 5904 unigenes were significantly changed after exposure to Cd or Pb stresses. Of these, 974 were co-up-regulated and 1281 were co-down-regulated under the two stresses. The transcriptome expression profiles of I. lactea var. chinensis under Cd or Pb stresses obtained in this study provided a resource for identifying common mechanisms in the detoxification of different heavy metals. Furthermore, the identified unigenes may be used for the genetic breeding of heavy-metal tolerant plants.

Role of two-sided crosstalk between NO and H2S on improvement of mineral homeostasis and antioxidative defense in Sesamum indicum under lead stress

H₂S and NO are two important gasotransmitters that modulate stress responses in plants. There are the contradictory data on crosstalk between NO and H₂S in the studies. Hence, in the present study, the role of interplay between NO and H₂S was assessed on the Pb tolerance of Sesamum indicum using pharmacological and biochemical approaches. Results revealed that Pb stress reduced the plant growth and the content of photosynthetic pigments and Fv/Fm ratio, increased the lipid peroxidation and the H₂O₂ content, elevated the endogenous contents of nitric oxide (NO), H₂S and enhanced the activities of antioxidant enzymes (except APX). Additionally, concentrations of most mineral ions (K, P, Mg, Fe, Mn and Zn) in both shoots and roots decreased. Pb accumulation in roots was more than it in shoots. Both sodium hydrosulfide (NaHS as a donor of H₂S) and sodium nitroprusside (SNP as an NO donor) improved the plant growth, the chlorophyll and carotenoid contents and PSII efficiency, reduced oxidative damage, increased the activities of antioxidant enzymes and reduced the proline content in Pb-stressed plants. Furthermore, both NaHS and SNP significantly restricted the uptake and translocation of Pb, thereby minimizing antagonistic effects of Pb on essential mineral contents in sesame plants. NaHS increased the NO generation and many NaHS-induced responses were completely reversed by cPTIO, as the specific NO scavenger. Applying SNP also enhanced H₂S release levels in roots of Pb-stressed plants and only some NO-driven effects were partially weakened by hypotuarine (HT), as the scavenger of H₂S.These findings proposed for the first time that two-sided interplay between H₂S and NO might confer an increased tolerance to Pb stress via activating the antioxidant systems, reducing the uptake and translocation of Pb, and harmonizing the balance of mineral nutrient.

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.

Phytoremediation of lead-contaminated soil by Sinapis arvensis and Rapistrum rugosum

Nowadays, public concern relating to ecological deleterious effects of heavy metals is on the rise. To evaluate the potential of Rapistrum rugosum and Sinapis arvensis in lead- contaminate phytoremediate, a pot culture experiment was conducted. The pots were filled by soil treated with different rates of leadoxide (PbO) including 0 (control), 100, 200, 300, 400, and 500 mg Pb per 1 kg soil. Germinated seeds were sown. Surprisingly, with increasing concentration of Pb, dry weight of R. rugosum and S. arvensis did not decrease significantly. In both of species, the concentration of Pb was higher in roots than shoots. In general, S.arvensis was absorbed more Pb compared to R. rugosum. The results revealed high potential of R. rugosum and S. arvensis in withdrawing Pb from contaminated soil. For both species, a positive linear relation was observed between Pb concentration in soil and roots. However, linear relationship was not observed between Pb concentration in the soil and shoots. Although both species test had low ability in translocation Pb from roots to shoots but they showed high ability in uptake soil Pb by roots. Apparently, these plants are proper species for using in phytoremediation technology.

Metal toxicity differently affects the Iris pseudacorus-arbuscular mycorrhiza fungi symbiosis in terrestrial and semi-aquatic habitats

Phytoremediation offers an environmental friendly alternative to conventional cleanup techniques. In this study, mycorrhizal fungi isolated from the roots of Mentha longifolia grown in the basin of the Centuria River (S Poland) were used. Iris pseudacorus was grown in substratum from an industrial waste, enriched in Pb, Fe, Zn, and Cd in a terrestrial and water-logged habitat. Plant yield and photosynthetic performance was the highest in the aquatic environment; however, the presence of toxic metals (TM) negatively affected photosystem II (PSII) photochemistry as shown by the JIP test. Fungi colonization and Cd accumulation within plant tissues was decreased. In the terrestrial habitat, neither arbuscular mycorrhizal fungi (AMF) nor metal toxicity affected plant growth, although metal uptake, Cd in particular, as well as photosynthesis were affected. Inoculated plants accumulated significantly more Cd, and photosynthesis was downregulated. The results presented in this study clearly indicate that the I. pseudacorus-AMF symbiosis adapts itself to the presence of toxic metals in the environment, optimizing resource supply, energy fluxes, and possibly stress tolerance mechanisms. Plant/AMF consortia grown in terrestrial and water-logged habitats utilize different strategies to cope with metal toxicity. The use of AMF in improving the phytoremediation potential of I. pseudacorus needs, however, further research.

Transcriptome Profiling of Louisiana iris Root and Identification of Genes Involved in Lead-Stress Response

Louisiana iris is tolerant to and accumulates the heavy metal lead (Pb). However, there is limited knowledge of the molecular mechanisms behind this feature. We describe the transcriptome of Louisiana iris using Illumina sequencing technology. The root transcriptome of Louisiana iris under control and Pb-stress conditions was sequenced. Overall, 525,498 transcripts representing 313,958 unigenes were assembled using the clean raw reads. Among them, 43,015 unigenes were annotated and their functions classified using the euKaryotic Orthologous Groups (KOG) database. They were divided into 25 molecular families. In the Gene Ontology (GO) database, 50,174 unigenes were categorized into three GO trees (molecular function, cellular component and biological process). After analysis of differentially expressed genes, some Pb-stress-related genes were selected, including biosynthesis genes of chelating compounds, metal transporters, transcription factors and antioxidant-related genes. This study not only lays a foundation for further studies on differential genes under Pb stress, but also facilitates the molecular breeding of Louisiana iris.

Antioxidant enzymes and proteins of wetland plants: their relation to Pb tolerance and accumulation

Constructed wetlands used to clean up toxic metals such as lead (Pb) from contaminated wastewater are considered as an effective and low-cost technology. The effect of Pb on the biomass, tolerance, soluble protein, and antioxidant enzymes in 18 candidate wetland plant species grown in soils without (control) and spiked with 900 and 1800 mg Pb kg(-1) was studied in a pot trial. Our pot experiment showed that the biomass, tolerance, and leaf protein contents decreased with increasing concentrations of Pb in soil. There were significant differences between the plants in their Pb tolerance indices (29-82 % in the 900 mg Pb kg(-1) amended soil) and also Pb uptake (13-749 mg kg(-1) in shoots and 1112-4891 mg kg(-1) in roots, in the same treatments). Activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves of most of the plants increased with increasing level of soil Pb concentration. Conversely, catalase (CAT) activity in leaves declined when plants were subjected to Pb stress. Lead accumulation by the 18 wetland plant species screened was strongly dependent on the species and Pb concentrations in the soil. However, Pb translocation from root to shoot was generally low in all species. Increases in SOD and POD activities suggest that the antioxidant system may play an important role in alleviating Pb toxicity in wetland plants. The data obtained should help in future species selection for the use in designing wetlands in Pb-contaminated environments.

Effects of exogenous glutathione and cysteine on growth, lead accumulation, and tolerance of Iris lactea var. chinensis

Effects of exogenous reduced glutathione (GSH) and cysteine (Cys) on growth, lead (Pb) accumulation, and nonprotein thiol (NPT) contents of Iris lactea var. chinensis under 100 and 500 mg L(-1) Pb stress were studied. Our results showed that 500 mg L(-1) Pb stress caused a dramatical decline in fresh weights, while the reduction of aboveground biomass was alleviated by exogenous GSH and Cys even though keeping higher Pb contents in roots and shoots. Exogenous GSH and Cys could enhance Pb accumulation in the shoots and roots compared with single Pb treatment. The promoting effect of GSH to Pb accumulation was larger than the effect of Cys, and the Pb contents in the shoots and roots treated with 500 mg L(-1) Pb + GSH reached 1,712 and 14,603 mg kg(-1), about 4.19 and 2.78 times of single 500 mg L(-1) Pb treatment, respectively. Microscopic imaging of Pb in roots and leaves showed that higher intensive fluorescence was observed in cell wall of root epidermis, stele, vascular tissues of the roots, and sclerenchyma cells of leaves treated with 500 mg L(-1) Pb + GSH and treated with 500 mg L(-1) Pb + Cys. Exogenous GSH had an apparent promoting effect on root and shoot GSH synthesis, while exogenous Cys reduced the synthesis of cellular GSH in shoot and increased Cys contents. Pb only induced the synthesis of phytochelatin (PC)2 in roots, and the PC2 content declined in GSH- and Cys-treated plant roots. These results suggested that GSH synthesis was a more effective approach to improve Pb accumulation and translocation of I. lactea var. chinensis. Further analysis of protein expression in plants by exogenous GSH and buthionine sulfoximine (BSO) application showed that the proteins regulated by GSH and BSO may constitute various enzymes involved in GSH biosynthesis and play certain roles in Pb accumulation and tolerance of I. lactea var. chinensis.

Overexpression of Iris. lactea var. chinensis metallothionein llMT2a enhances cadmium tolerance in Arabidopsis thaliana

Metallothioneins (MTs) are cysteine-rich, low molecular weight, heavy metal-binding protein molecules. Here, a full-length cDNA homologue of MT2a (type 2 metallothionein) was isolated from the cadmium-tolerant species Iris. lactea var. chinensis (I. lactea var. chinensis). Expression of IlMT2a in I. lactea var. chinensis roots and leaves was up-regulated in response to cadmium stress. When the gene was constitutively expressed in Arabidopsis thaliana (A. thaliana), root length of transgenic lines was longer than that of wild-type under 50μM or 100μM cadmium stress. However, there was no difference of cadmium absorption between wild-type and trangenic lines. Histochemical staining by 3,3-diaminobenzidine (DAB) and nitroblue tetrazoliu (NBT) clearly demonstrated that transgenic lines accumulated remarkably less H2O2 and O2(-) than wild-type. Together, IlMT2a may be a promising gene for the cadmium tolerance improvement.

Reference gene selection for quantitative real-time RT-PCR normalization in Iris. lactea var. chinensis roots under cadmium, lead, and salt stress conditions

Quantitative real time PCR (RT-qPCR) has emerged as an accurate and sensitive method to measure the gene expression. However, obtaining reliable result depends on the selection of reference genes which normalize differences among samples. In this study, we assessed the expression stability of seven reference genes, namely, ubiquitin-protein ligase UBC9 (UBC), tubulin alpha-5 (TUBLIN), eukaryotic translation initiation factor (EIF-5A), translation elongation factor EF1A (EF1 α ), translation elongation factor EF1B (EF1b), actin11 (ACTIN), and histone H3 (HIS), in Iris. lactea var. chinensis (I. lactea var. chinensis) root when the plants were subjected to cadmium (Cd), lead (Pb), and salt stress conditions. All seven reference genes showed a relatively wide range of threshold cycles (C t ) values in different samples. GeNorm and NormFinder algorithms were used to assess the suitable reference genes. The results from the two software units showed that EIF-5A and UBC were the most stable reference genes across all of the tested samples, while TUBLIN was unsuitable as internal controls. I. lactea var. chinensis is tolerant to Cd, Pb, and salt. Our results will benefit future research on gene expression in response to the three abiotic stresses.

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.

Lead-induced oxidative damage in steriled seedlings of Nymphoides peltatum

The effects of increasing concentrations of lead (Pb) on Pb accumulation and its influence on nutrient elements, malondialdehyde (MDA) content, generation of superoxide anion (O2(-·)), hydrogen peroxide (H2O2) content, antioxidant enzymes activities, soluble protein, and photosynthetic pigment, as well as chloroplast ultrastructure in steriled seedlings of Nymphoides peltata (S. G. Gmel.) Kuntze were investigated in order to understand Pb-induced toxicity. The accumulation of Pb was found to increase in a concentration-dependent manner. Nutrient elements (Ca, K, Fe, Mn, and Mo) were also affected. MDA content and O2(-·) generation rate increased progressively, while H2O2 content first boosted up at a low Pb concentration of 12.5 μM but then declined. Guaiacol peroxidase and catalase activities increased alternately, while superoxide dismutase activity gradually fell. Negative correlations were found between Pb and soluble protein and photosynthetic pigment. Moreover, Pb exposure resulted in a significant damage of chloroplasts. Taken together, these findings supported the hypothesis that Nymphoides peltatum underwent oxidative stress induced by Pb. In addition, both the disorder of nutrient elements and the damage to the ultrastructure of chloroplasts were indicative of general disarray in the cellular functions exerted by Pb.

Lead tolerance in plants: strategies for phytoremediation

Lead (Pb) is naturally occurring element whose distribution in the environment occurs because of its extensive use in paints, petrol, explosives, sludge, and industrial wastes. In plants, Pb uptake and translocation occurs, causing toxic effects resulting in decrease of biomass production. Commonly plants may prevent the toxic effect of heavy metals by induction of various celular mechanisms such as adsorption to the cell wall, compartmentation in vacuoles, enhancement of the active efflux, or induction of higher levels of metal chelates like a protein complex (metallothioneins and phytochelatins), organic (citrates), and inorganic (sulphides) complexes. Phyotochelains (PC) are synthesized from glutathione (GSH) and such synthesis is due to transpeptidation of γ-glutamyl cysteinyl dipeptides from GSH by the action of a constitutively present enzyme, PC synthase. Phytochelatin binds to Pb ions leading to sequestration of Pb ions in plants and thus serves as an important component of the detoxification mechanism in plants. At cellular level, Pb induces accumulation of reactive oxygen species (ROS), as a result of imbalanced ROS production and ROS scavenging processes by imposing oxidative stress. ROS include superoxide radical (O2(.-)), hydrogen peroxide (H2O2) and hydroxyl radical ((·)OH), which are necessary for the correct functioning of plants; however, in excess they caused damage to biomolecules, such as membrane lipids, proteins, and nucleic acids among others. To limit the detrimental impact of Pb, efficient strategies like phytoremediation are required. In this review, it will discuss recent advancement and potential application of plants for lead removal from the environment.

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

The physiological responses and Cu accumulation of Paulownia fortunei (Seem) Hemsl. were studied under 15.7-157 μmol L(-1) Cu treatments in liquid culture for 14 days; the impacts of Cu concentration in the seedlings were evaluated under Cu mine tailing culture with acetic acid and EDTA treatment for 60 days. Results showed that the concentrations of Chl-a, Chl-b and Carotenoids significantly increased (p < 0.05) at 15.7-78.7 μmol L(-1)Cu treatment and significantly decreased at 157 μmol L(-1) treatment after 14 days of Cu exposure. The activities of superoxide dismutase (SOD) and catalase (CAT) significantly increased as Cu levels were enhanced and the activities of both SOD and CAT under 157 μmol L(-1) Cu stress were 2.9 and 1.9 times higher than that of control, respectively. The concentrations of proline and soluble sugars in the leaves of P. fortunei significantly increased as the Cu concentrations were elevated. Cu concentrations in roots, stems and leaves of P. fortunei increased significantly as Cu levels increased and reached 1911, 101 and 93 μg g(-1) dry weights (DW) at 157 μmol L(-1) Cu treatment, respectively. The seedlings of P. fortunei cultivated in Cu tailing experienced unsuccessful growth and loss of leaves in all treatments due to poor nutrition of the Cu tailing. The dry weight of P. fortunei increased under all the treatments of acetic acid after 60 days exposure. However, dry weight significantly decreased under both levels of EDTA. The Cu concentrations increased significantly in roots and decreased in leaves when each was treated with both concentrations of acetic acid. The Cu concentrations in the roots, stems and leaves increased significantly, and the concentrations of Cu in the stems and leaves under the treatment of 2 μmol L(-1) EDTA reached 189.5 and 763.1 μg g(-1) DW, respectively. The result indicated that SOD, CAT, proline and soluble sugars played an important role in coping with the oxidative stress of copper. Acetic acid could promote growth and EDTA at the experimental levels, which could also enhance Cu absorption and translocation into the stems and leaves of P. fortune. Furthermore, acetic acid and EDTA could be rationally utilized in Cu-contaminated soil.

Effects of lead on the growth, lead accumulation and physiological responses of Pluchea sagittalis

This work aimed to study the process of stress adaptation in root and leaves of different developmental stages (apex, middle and basal regions) of Pluchea sagittalis (Lam.) Cabrera plants grown under exposure to five Pb levels (0, 200, 400, 600 and 1000 μM) for 30 days. Pb concentration and content in roots, stems, and leaves of different developmental stages increased with external Pb level. Consumption of nutrient solution, transpiration ratio, leaf fresh weight, leaf area, and shoot length decreased upon addition of Pb treatments. However, dry weight of shoot parts and roots did not decrease upon addition of Pb treatments. Based on index of tolerance, the roots were much more tolerant to Pb than shoots. δ-aminolevulinic acid dehydratase activity was decreased by Pb treatments, whereas carotenoid and chlorophyll concentrations were not affected. Lipid peroxidation and hydrogen peroxide concentration both in roots and leaves increased with increasing Pb levels. Pb treatments increased ascorbate peroxidase activity in all plant parts, while superoxide dismutase activity increased in leaves and did not change in roots. Catalase activity in leaves from the apex shoot was not affected by Pb, but in other plant parts it was increased. Pb toxicity caused increase in non-protein thiol groups concentration in shoot parts, whereas no significant difference was observed in roots. Both root and shoot ascorbic acid concentration increased with increasing Pb level. Therefore, it seems that Pb stress triggered an efficient defense mechanism against oxidative stress in P. sagittalis but its magnitude was depending on the plant organ and of their physiological status. In addition, these results suggest that P. sagittalis is Pb-tolerant. In conclusion, P. sagittalis is able to accumulate on average 6730 and 550 μg Pb g(-1) dry weight, respectively, in the roots and shoot, a physiological trait which may be exploited for the phytoremediation of contaminated soils and waters.

The physiological response and sub-cellular localization of lead and cadmium in Iris pseudacorus L

The seedling development and physiological responses of Iris pseudacorus L. to Pb and Cd and their combination were studied for 28 days liquid culture and sub-cellular localization of Pb and Cd in the root tip cells treated with 2,070 mg L(-1) Pb and 1,000 mg L(-1)Cd for 16 days sand culture was evaluated. Results showed that the dry weights (DWs) of shoots and roots of I. pseudacorus were significantly decreased at 500 mg L(-1)Pb and 25 mg L(-1)Cd + 500 mg L(-1)Pb treatments and the root DWs under all treatments were significantly decreased in comparison with that of control. The concentrations of Chla in the leaves were decreased at all treatments, while, the concentrations of Chlb and total carotenoids were not significantly decreased under 25 mg L(-1)Cd and 25 mg L(-1)Cd + 500 mg L(-1)Pb treatments. The MDA and proline concentrations and POD activities in the shoots and roots were increased under treatments of 500 mg L(-1)Pb and 25 mg L(-1)Cd + 500 mg L(-1)Pb, but POD activities in the shoots and roots and MDA concentrations in the shoots were significantly decreased at 25 mg L(-1) Cd treatment. The results of sub-cellular localization of Pb and Cd showed that numerous Pb deposits were found on the inner surface of died cell walls in the cortex treated with 2,070 mg L(-1) Pb and Cd deposits were found in the cell wall treated with 1,000 mg L(-1) Cd. Pb and Cd deposits were not found in the cytoplasm. The results indicated that POD and proline showed strong beneficial properties against Pb and Cd stress and there were some mechanisms keeping most cells with normal activities in the plant from Pb toxicity by sacrificing a few cells that accumulated a large amount Pb. Sub-cellular localizations of Pb and Cd in the root tip cells of I. pseudacorus were little difference with the localizations in other species of Iris in the previous studies.