Cd Hyperaccumulator Research Articles

Occurrence and Uptake of Heavy Metals in Soil and Plant (Tomato) Associated with Crude Oil Contamination

The general increase of heavy metal content in the soil has been largely caused by crude oil spillage. This study investigates the possibility of tomato (Lycopersicon esculentum Miller) to sorb heavy metals present in crude oil. Crude oil of 0 mL (control), 75 and 150 mL were mixed thoroughly with 15 kg of loamy soil (dry weight) in perforated plastic buckets, as the experimental pots and left for 4 days before transplanting tomato seedlings. After 12 weeks of transplanting, heavy metals analysis was carried out on plant’s fruits, leaves, stems and roots. Physicochemical analyses show that control soil had the lowest organic carbon (3.07 %) while 150 mL had the highest mean organic carbon content (8.24 %). The silt, clay and sand constituents were not significantly different (p > 0.05) in both treated and untreated soil. The control had the least pH value (6.1) while the lead (Pb) content in soil was highest in 150 mL (0.33 mg/kg) but was not significantly different (p > 0.05) from control (0.26 ) and 75 mL (0.30 mg/kg). Lead (Pb) and Cadmium (Cd) were not detected in leaves and fruits. However, bioaccumulation factor (BAF) of Cd and Ni in stem were greater than 1. Although, the concentrations of these heavy metals falls below toxic levels, its consumption could lead to adverse health effects in both man and animals through bioaccumulation or biomagnification.
 HIGHLIGHTS
 
 Countries with poor hydrocarbon pollution regulation are more challenging with oil spills, either through accidental discharges or indiscriminate disposal of hydrocarbon waste
 Plants essentially need some metals such as iron, copper among others, for their growth and other metabolic activities. However, at excess of specific limits, these metals adversely affect plant growth
 In this study, bioaccumulation factors (BAF) of Cd and Ni in the stem were greater than 1, this shows that the tomato plant is a hyperaccumulator of Cd and Ni from the soil
 
 GRAPHICAL ABSTRACT

Cosmopolitan cadmium hyperaccumulator Solanum nigrum: Exploring cadmium uptake, transport and physiological mechanisms of accumulation in different ecotypes as a way of enhancing its hyperaccumulative capacity

The non-essential element cadmium (Cd) is one of the most problematic priority soil pollutants due to multitude of pollution sources, mobility in the environment and high toxicity to all living organisms. This strongly limits also the number and occurrence of species – Cd hyperaccumulators to be used for soil phytoremediation. However, efficient Cd hyperaccumulator Solanum nigrum L. appeared to commonly occur worldwide as a representative of Solanum nigrum complex of a great taxonomic diversity. This led to the idea that the search among different ecotypes of Solanum nigrum L. may result in the identifying the most efficient Cd hyperaccumulator without applying to soil any additional measures such as chemical ligands. In this first pioneering comparative study, three randomly selected ecotypes of S. nigrum L. ssp. nigrum from Shenyang (SY) and Hanzhong (HZ) in China, and Kyoto (KY) in Japan were used in pot experiments at soil treatments from 0 to 50 mg Cd kg−1. The Cd accumulation capacity appeared to represent KY > HZ > SY range, KY ecotype accumulating up to 73%, and HZ ecotype up to 67% bigger total Cd load than SY ecotype. At Cd content in soil up to 10 mg kg−1, no significant effect on the all ecotype biomass, photosynthetic activities, contents of first line defense antioxidant enzymes (CAT, SOD, GPX), and scavenging antioxidants ASA, GSH, was observed. At Cd in soil>10 mg kg−1all these parameters showed decreasing, and cell damage indicator MDA increasing trend, however total accumulated Cd load further increased up to 30 mg kg Cd in soil in all ecotypes in the same KY > HZ > SY sequence. The study proved the great potential of enhancing Cd accumulation capacity of S. nigrum species by selecting the most efficient ecotypes among commonly occurring representatives of S. nigrum complex worldwide. Moreover, these first comparative experiments convinced that the cosmopolitan character and great variety of species/subspecies belonging to Solanum nigrum complex all over the world opens the new area for successful soil phytoremediation with the use of the most appropriate eco/genotypes of S. nigtum as a tool for the best Cd-contaminated soil management practice.

Remediation Potential of Taraxacum kok-saghyz Rodin on Lead and Cadmium Contaminated Farmland Soil

Taraxacum kok-saghyz Rodin (TSK) is an energy plant that can be used as a raw material for natural rubber. The aim of this study was to examine the remediation potential of TSK to lead (Pb)- and cadmium (Cd)-contaminated farmland soil. In this study, a pot experiment was conducted, and the "Soil Environmental Quality and Agricultural Land Soil Pollution Risk Control Standard (GB 15618-2018)" was used as reference. We set up four different concentrations of Pb and Cd pollution treatment to study the characteristics of the accumulation and tolerance of TSK to Pb and Cd. The results showed that as the content of Pb and Cd in the soil increased, the chlorophyll content and biomass of TSK gradually decreased, and the SOD, POD, and CAT enzyme activities gradually increased. The BCF and TF of Cd were between 1.20 and 1.50, indicating that TSK presented some characteristics of a Cd hyperaccumulator. The BCF and TF of Pb were between 0.71 and 1.11. Thus, TSK was a good Pb enrichment plant and possessed the potential to repair soil with ω(Pb) below 400 mg·kg-1. The accumulation of Pb and Cd gradually increased, and the maximum accumulation of Cd and Pb in the shoots was 9.832 μg·plant-1 and 1091.185 μg·plant-1, respectively. However, in lower concentrations of Pb- and Cd-contaminated soil, the removal rate was greater, and the remediation efficiency was better. Overall, using TSK to repair Pb- and Cd-contaminated farmland soil has good application prospects and economic value.

Mechanism exploration of Solanum nigrum L. hyperaccumulating Cd compared to Zn from the perspective of metabolic pathways based on differentially expressed proteins using iTRAQ

It is challenging to determine the mechanism involved in only Cd hyperaccumulation by Solanum nigrum L. owing to the uniqueness of the process. Isobaric tags for relative and absolute quantitation (iTRAQ) were used to explore the mechanism by which S. nigrum hyperaccumulates Cd by comparing the differentially expressed proteins (DEPs) for Cd and Zn accumulation (non-Zn hyperaccumulator). Based on the comparison between the DEPs associated with Cd and Zn accumulation, the relative metabolic pathways reflected by 17 co-intersecting specific proteins associated with Cd and Zn accumulation included phagosome, aminoacyl-tRNA biosynthesis, and carbon metabolism. Apart from the 17 co-intersecting specific proteins, the conjoint metabolic pathways reported by 21 co-intersecting specific proteins associated with Cd accumulation and 30 co-intersecting specific proteins associated with Zn accumulation, the most differentially expressed metabolic pathways might cause Cd TF (Translocation factor)> 1 and Zn TF< 1, including protein export, ribosome, amino sugar, and nucleotide sugar metabolism. The determined DEPs were verified using qRT-PCR with the four key proteins M1CW30, A0A3Q7H652, A0A0V0IFB9, and A0A0V0IAC4. The plasma membrane H+-ATPase protein was identified using western blotting. Some physiological indices for protein-related differences indirectly confirmed the above results. These results are crucial to further explore the mechanisms involved in Cd hyperaccumulation.

Trace Elements Uptake in Brassica rapa chinensis Cultivated in Ultrabasic (Oxisol) and Ultisol Soils, North Borneo

The study aims to investigate the soil physico-chemical properties and trace elements uptake of Brassica rapa chinensis plants cultivated in ultrabasic (oxisol) and ultisoil soil of Ranau, North Borneo, Malaysia by inductively coupled plasma-optical emission spectrometry (ICP-OES). This study can contribute to propose a more sustainable soil management practice. All selected trace elements bioavailability in ultrabasic soil was significantly higher than ultisols except for Ca and Cd. There was no significant amount of difference in soil pH (slightly acidic) and electrical conductivity (slightly saline) between these soil types. However, a significant amount of difference between the percentage of soil moisture and organic matter between ultrabasic and ultisol soils was observed. These might contribute to the uptake of elements into the studied plant. The B. rapa chinensis is a hyperaccumulator of Cd and Pb for both type of soils. The B. rapa chinensis is an accumulator of As when grown in ultrabasic soil, while an accumulator of Co when grown in ultisol soil. Although Pb was not detected in ultisol soil as compared to ultrabasic soil, the concentration of Pb in plants cultivated in ultisol soil had exceeded the maximum permissible limit of Malaysia Food Regulation 1985. Soil amendment in frequently use agriculture sites needs to be conducted such as the addition of organic matter to reduce transfers of trace elements from soil to plants that can pose toxicity risk.

Phytoextraction potential of arsenic and cadmium and response of rhizosphere microbial community by intercropping with two types of hyperaccumulators.

Intercropping with hyperaccumulators/accumulators is a promising alternative to enhance phytoextraction of heavy metal(loid)s in contaminated soil. In this research, a pot experiment was conducted to evaluate the influences of intercropping As hyperaccumulator Pteris vittata L. with Cd hyperaccumulator Sedum alfredii Hance or accumulator Hylotelephium spectabile (Boreau) H. Ohba on the plant growth, As and Cd phytoextraction, and rhizosphere bacterial microbiota. The results indicated that intercropping can promote the growth of plants. The total biomass of P. vittata, S. alfredii, and H. spectabile in intercropping systems was improved by 19.9-34.1%, 16.8%, and 11.5%, respectively, in comparison with corresponding plant monoculture. The As content in rhizoid and frond of P. vittata when intercropped with S. alfredii was significantly increased by 28.3% and 19.0% (P < 0.05), respectively, as compared with P. vittata monoculture, and this treatment acquired the maximum As and Cd accumulation with 2032 μg·pot-1 and 397 μg·pot-1, respectively. Intercropping enhanced the soil bacterial community diversity. The genera of Lysobacter in P. vittata rhizosphere and Massilia and Arthrobacter in S. alfredii rhizosphere had higher abundance in the intercropping system of P. vittata and S. alfredii. There were significantly positive correlation relationships between Massilia and Arthrobacter with plant Cd content and Lysobacter with plant As content, indicating that they may play important roles in As and Cd phytoextraction. The results suggested that intercropping P. vittata with S. alfredii could be a potential strategy for phytoextraction of As and Cd from co-contaminated soil.

Effects of four endophytic bacteria on cadmium speciation and remediation efficiency of Sedum plumbizincicola in farmland soil.

Cadmium (Cd) pollution in farmland soils severely affects agricultural production safety, thereby threatening human health. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. This study was aimed to improve the remediation effect of S. plumbizincicola on Cd-contaminated farmland soil and provide a theoretical basis for the enhancement of endophytic bacteria in the repair of Cd-contaminated soil with S. plumbizincicola. Four kinds of endophytic bacteria, namely Buttiauxella, Pedobacter, Aeromonas eucrenophila, and Ralstonia pickettii, were used, and soil culture experiments and pot experiments were conducted to explore the effects of endophytic bacteria on soil Cd speciation and phytoremediation efficiency of Cd-contaminated farmland soils. Under the experimental conditions, after inoculation with endophytic bacteria, the soil pH was effectively reduced, content of weak acid-extracted Cd and oxidizable Cd increased, and content of reducible Cd and residual Cd decreased. Soil Cd activity was increased, and the availability coefficient of soil Cd increased by 1.15 to 6.41 units compared with that of the control (CK2). Compared with CK2, the biomass of S. plumbizincicola significantly increased by 23.23-55.12%; Cd content in shoots and roots of S. plumbizincicola increased by 29.63-46.01% and 11.42-84.47%, respectively; and bioconcentration factor was 2.13 to 2.72 times that of CK2. The Cd removal rate of S. plumbizincicola monocropping was 48.25%. When S. plumbizincicola was planted with inoculating endophytic bacteria, the Cd removal rate in the soil reached 61.18-71.49%, which was significantly higher than that of CK2 (p < 0.05). The treatment with endophytic bacteria activated soil Cd, promoted the growth of S. plumbizincicola, increased its Cd content, and enhanced the phytoremediation of Cd-contaminated farmland soil. Therefore, endophytic bacteria can be used to improve the remediation efficiency of S. plumbizincicola in Cd-contaminated farmland soils.

Enolase, a cadmium resistance related protein from hyperaccumulator plant Phytolacca americana, increase the tolerance of Escherichia coli to cadmium stress

Phytolacca americana is a Cd hyperaccumulator plant that accumulates significant amounts of Cd in leaves, making it a valuable phytoremediation plant species. Our previous research found enolase (ENO) may play an important part in P. americana to cope with Cd stress. As a multifunctional enzyme, ENO was involved not only in glycolysis but also in the response of plants to various environmental stresses. However, there are few studies on the function of PaENO (P. americana enolase) in coping with Cd stress. In this study, the PaENO gene was isolated from P. americana, and the expression level of PaENO gene significantly increased after Cd treatment. The enzymatic activity analysis showed PaENO had typical ENO activity, and the 42-position serine was essential to the enzymatic activity of PaENO. The Cd resistance assay indicated the expression of PaENO remarkably enhanced the resistance of E. coli to Cd, which was achieved by reducing the Cd content in E. coli. Moreover, both the expression of inactive PaENO and PaMBP-1 (alternative translation product of PaENO) can improve the tolerance of E. coli to Cd. The results indicated PaENO may be alternatively translated into the transcription factor PaMBP-1 to participate in the response of P. americana to Cd stress.

Phytoremediation Potential of Selected Ornamental Woody Species to Heavy Metal Accumulation in Response to Long-Term Irrigation with Treated Wastewater

Arid and semiarid environments of Mediterranean countries suffer from scarcity of water resources, which limits their agriculture productivity. Using treated wastewater (TWW) is considered an alternative strategy for irrigation purposes in such areas. However, TWW contains substantial levels of heavy metals (HMs) and contaminants that pollute the environment and soil. The aim of this study is to evaluate the phytoremediation potential of six selected woody tree species under long-term irrigation with TWW. The concentration, bioaccumulation factor (BFC), translocation factor (TF), and comprehensive bioconcentration index (CBCI) of HMs were measured in the various parts (roots, bark, and leaves) of the studied tree species. The results show a general pattern of mineral accumulation in the roots and low translocation to the areal parts of various species. Cupressus sempervirens, which is a native species in Mediterranean environments, had higher TF values for Fe, Mn, Cu, Cr, Cd, and Pb metals in its areal parts compared to other tree species. The study shows that Ficus nitida has the potential to be a hyperaccumulator for Cd in its bark, with a TF value that exceeds 12. Deciduous trees species (Populus nigra and Robinia pseudoacacia) were found to have high TF values for Ni and Cd toward their areal parts, whereas a higher TF for Cr (1.21) was only found in P. nigra bark. Cupressus sempervirens had, significantly, the highest bark and leaf CBCI values (0.83 and 0.82, respectively), whereas Ficus nitida had the second-highest values in the bark and leaves (0.56 and 0.51, respectively). Therefore, Cupressus sempervirens and Ficus nitida are considered good hyperaccumulators for various HMs, and can be used for phytoremediation activities in polluted areas.

The Potential of Nitrogen Applied Rapeseed (Brassica napus L) in Remediation of Cadmium Polluted Soil

This study aims to determine the Cd accumulation levels of rapeseed (Brassica napus L.) based on nitrogen (N) (0, 100, 200 and 400 mg kg-1) and Cd (0, 1.5, 3 and 6 mg kg-1) applications to the soil on pot trials conducted under controlled environmental conditions. The highest chlorophyll content was obtained at 400 mg N kg-1 without Cd. The highest dry weight amount in rapeseed was obtained with the application of 100 mg N kg-1 × 1.5 mg Cd kg-1, however, the highest rates of both N and Cd resulted in the lowest dry weight. In 400 mg N kg-1 × 6 mg Cd kg-1 (131 mg Cd kg-1) and 200 mg N kg-1 × 6 mg Cd kg-1 (113.80 mg Cd kg-1) applications, Cd concentration of the rapeseed was determined to be higher than critical Cd hyperaccumulation level. The capacity of Cd uptake and accumulation in rapeseed shoots were enhanced with N applications, thus promoting the phytoextraction of Cd from Cd-contaminated soils. Cadmium rates did not affect Fe, Cu, Mn and Zn uptake levels when N was not applied. However, Cd ratios increased the microelement uptake levels, except Zn, when applied to 100 and 200 N kg-1 ratios as compared to control plants. Eventually, increase in Cd uptake of plants with N fertilization is possible; however, excessive N rates may not result in an increase in rapeseed biomass.

Enhancing the Phytoremediation of Heavy Metals by Combining Hyperaccumulator and Heavy Metal-Resistant Plant Growth-Promoting Bacteria.

Heavy metals (HMs) have become a major environmental pollutant threatening ecosystems and human health. Although hyperaccumulators provide a viable alternative for the bioremediation of HMs, the potential of phytoremediation is often limited by the small biomass and slow growth rate of hyperaccumulators and HM toxicity to plants. Here, plant growth-promoting bacteria (PGPB)-assisted phytoremediation was used to enhance the phytoremediation of HM-contaminated soils. A PGPB with HM-tolerant (HMT-PGPB), Bacillus sp. PGP15 was isolated from the rhizosphere of a cadmium (Cd) hyperaccumulator, Solanum nigrum. Pot experiments demonstrated that inoculation with strain PGP15 could significantly increase the growth of S. nigrum. More importantly, strain PGP15 markedly improved Cd accumulation in S. nigrum while alleviating Cd-induced stress in S. nigrum. Specifically, PGP15 inoculation significantly decreased the contents of H2O2, MDA, and in S. nigrum, while the activities (per gram plant fresh weight) of SOD, APX, and CAT were significantly increased in the PGP15-inoculated plants compared with the control sample. These results suggested that the interactions between strain PGP15 and S. nigrum could overcome the limits of phytoremediation alone and highlighted the promising application potential of the PGPB-hyperaccumulator collaborative pattern in the bioremediation of HM-contaminated soils. Furthermore, the PGP15 genome was sequenced and compared with other strains to explore the mechanisms underlying plant growth promotion by HMT-PGPB. The results showed that core genes that define the fundamental metabolic capabilities of strain PGP15 might not be necessary for plant growth promotion. Meanwhile, PGP15-specific genes, including many transposable elements, played a crucial role in the adaptive evolution of HM resistance. Overall, our results improve the understanding of interactions between HMT-PGPB and plants and facilitate the application of HMT-PGPB in the phytoremediation of HM-contaminated soils.

Leaf Functional Traits of Invasive Grasses Conferring High-Cadmium Adaptation Over Natives

Heavy metal (HM) contamination resulting from industrialization and urbanization during the Anthropocene along with plant invasion can severely threaten the growth and adaptation of local flora. Invasive alien plant species generally exhibit a growth pattern consistent with their functional traits in non-contaminated environments in the introduced range. However, it remains unclear whether invasive alien plants have an advantage over native plants in contaminated environments and whether this growth pattern is dependent on the adaptation of their leaf functional traits. Here, we selected two congeneric pairs of invasive alien and native grasses that naturally co-exist in China and are commonly found growing in contaminated soil. To evaluate the effect of cadmium (Cd) on the structural and physiological leaf traits, we grew all four species in soil contaminated without or with 80 mg/kg Cd. Invasive plants contained significantly higher concentrations of Cd in all three organs (leaf, stem, and root). They displayed a higher transfer factor and bioconcentration factor (BCF) of shoot and root than natives, indicating that invasive species are potential Cd hyperaccumulators. Invasive plants accumulated polyphenol oxidase (PPO) to higher levels than natives and showed similar patterns of leaf structural and physiological traits in response to changes in Cd bioconcentration. The quantifiable leaf structural traits of invasive plants were significantly greater (except for stomatal density and number of dead leaves) than native plants. Leaf physiological traits, chlorophyll content, and flavonoid content were also significantly higher in invasive plants than in natives under Cd stress conditions after 4 weeks, although nitrogen balance index (NBI) showed no significant difference between the two species. Chlorophyll fluorescence parameters decreased, except for the quantum yield of photosystem II (ΦPSII) and the proportion of open photosystem II (qP), which increased under Cd stress conditions in both species. However, invasive plants exhibited higher fluorescence parameters than natives under Cd stress, and the decrement observed in invasive plants under Cd stress was greater than that in natives. High Cd adaptation of invasive grasses over natives suggests that invasive plants possess optimal leaf structural and physiological traits, which enable them to adapt to stressful conditions and capture resources more quickly than natives. This study further emphasizes the potential invasion of alien plants in contaminated soil environments within the introduced range. To a certain extent, some non-invasive alien plants might adapt to metalliferous environments and serve as hyperaccumulator candidates in phytoremediation projects in contaminated environments.

Enhanced Cd Phytoextraction by Solanum nigrum L. from Contaminated Soils Combined with the Application of N Fertilizers and Double Harvests.

It is very important to increase phytoremediation efficiency in practice in suitable climatic conditions for plant growth through multiple harvests. Solanum nigrum L. is a Cd hyperaccumulator. In the present experiment, after applying different types of N fertilizers (NH4HCO3, NH4Cl, (NH4)2SO4, CH4N2O), root and shoot biomasses and Cd phytoextraction efficiency of S. nigrum effectively improved (p < 0.05). Shoot biomasses of S. nigrum harvested at the first florescence stage plus the amounts at the second florescence stage were higher than those harvested at the maturation stage, which indicates that S. nigrum Cd phytoaccumulation efficiency was higher in the former compared to the latter as there was no clear change in Cd concentration (p < 0.05). The pH value and extractable Cd contents showed no changes, regardless of whether N fertilizer was added or not at different growth stages. In addition, after N fertilizer was applied, H2O2 and malondialdehyde (MDA) contents in S. nigrum in vivo were lower compared to those that had not received N addition (CK); similarly, the concentration of proline was decreased as well (p < 0.05). The activity of the antioxidant enzyme catalase (CAT), harvested at different growth periods after four types of N fertilizer applications, obviously decreased in S. nigrum shoots, while peroxidase (POD) and superoxide dismutase) (SOD) activities increased (p < 0.05). Our study demonstrated that (NH4)2SO4 treatment exerted the most positive effect and CH4N2O the second most positive effect on S. nigrum Cd phytoremediation efficiency in double harvests at florescence stages, and the growth conditions were better than others.

Cadmium removal potential of hyperaccumulator Solanum nigrum L. under two planting modes in three years continuous phytoremediation

Solanum nigrum L. is a Cd hyperaccumulator, but the potential for continuous remediation, or different planting methods have not been fully characterized. The potential for continuous phytoremediation of Cd-contaminated farmland soil (2.08 mg kg−1 Cd) by 2 planting methods (flowering harvest twice a year and maturity harvest once a year) was studied in a 3-year pot experiment. The total Cd accumulation (ug plant−1) of the 3-year flowering stage treatments was 26.3% higher than that of the maturity stage treatments, which was mainly due to that flowering harvest twice a year caused 65.5% increase of shoot biomass. Similarly, the Cd decreased concentration in soil and Cd removal rate in the flowering stage treatments were 29.2% and 27.9% higher than that in the maturity stage treatments, respectively. After 3 years of phytoremediation, the extractable Cd concentration in soil was reduced by 36.4% in the flowering stage treatments and by 27.6% in the maturity stage treatments, which also led to the same decreasing trend of Cd accumulation of S. nigrum. In conclusion, the study results have demonstrated that the planting mode of two harvests a year at the flowering stage seems to be a viable option to apply for continuous phytoremediation of Cd-contaminated farmland soil.

Remediation and Micro-Ecological Regulation of Cadmium and Arsenic Co-Contaminated Soils by Rotation of High-Biomass Crops and Sedum alfredii Hance: A Field Study

Rotation of high-biomass crops and hyperaccumulators is considered to be an effective, safe and economical method for the remediation of medium-mild heavy metal contaminated soil, but the present studies pay more attention to the removal efficiency rather than changes in soil micro-ecology. In order to explore the remediation effect of hyperaccumulators rotated with high-biomass crops on Cd and As co-contaminated soil, Cd hyperaccumulator ecotype (HE) Sedum alfredii Hance and crops were selected to construct a field experiment, five rotation modes including Sedum alfredii Hance-Oryza sativa L. (SP), Sedum alfredii Hance-Sorghum bicolor (L.) Moench (SS), Sedum alfredii Hance-Zea mays L. (SM), Sedum alfredii Hance-Hibiscus cannabinus L. (SK), Sedum alfredii Hance-Trichosanthes kirilowii Maxim. (ST), and investigated the effects of these modes on the removal efficiency, soil physiochemical properties and micro-ecological effects (soil nutrients, enzyme activities and microbial diversity) through a field experiment. The results showed that total soil Cd from the five rotation modes (SP, SS, SM, SK and ST) decreased by 25.1%, 20.3%, 34.5%, 6.3% and 74.3%, respectively, and total soil As decreased by 42.9%, 19.8%, 39.7%, 39.7% and 45.7%, respectively. The rotation significantly increased soil organic matter by 47.39–82.28%, effectively regulated soil pH value and cation exchange capacity. The rotation modes also significantly increased soil alkali-hydrolysable nitrogen by 9.09–50.91%, but decreased soil available phosphorus and rapidly available potassium. Except for urease, the soil enzyme activities increased overall. The Alpha diversity increased, and soil microbial structure optimized after rotation. ST mode was the most effective remediation mode, which not only reduces the content of Cd and As in the soil, but also effectively regulates the soil micro-ecology. The results from this study have shown that it is feasible to apply Sedum alfredii Hance and the high-biomass rotation method for the remediation of Cd and As co-contaminated soil.

Phytochemical analysis reveals an antioxidant defense response in Lonicera japonica to cadmium-induced oxidative stress

Cadmium (Cd), though potentially beneficial at lower levels to some plant species, at higher levels is a toxic metal that is detrimental to plant growth and development. Cd is also a carcinogen to humans and other contaminated plant consumers, affecting the kidneys and reducing bone strength. In this study we investigated responses of growth, chlorophyll content, reactive oxygen species levels, and antioxidant responses to Cd in honeysuckle leaves (Lonicera japonica Thunb.), a potential Cd hyperaccumulator. Results indicated that plant height, dry weight, leaf area, and chlorophyll content increased when honeysuckle was exposed to 10 mg kg−1 or 30 mg kg−1 Cd (low concentration). However, in response to 150 mg kg−1 or 200 mg kg−1 Cd (high concentration) these growth parameters and chlorophyll content significantly decreased relative to untreated control plant groups. Higher levels of superoxide radical (O2·−) and hydrogen peroxide (H2O2) were observed in high concentration Cd groups. The activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase were enhanced with exposure to increasing levels of Cd. Additionally, the Ascorbate–Glutathione (AsA–GSH) cycle was activated for the removal of H2O2 in honeysuckle in response to elevated Cd. The Pearson correlation analysis, a redundancy analysis, and a permutation test indicated that proline and APX were dominant antioxidants for removing O2·− and H2O2. The antioxidants GSH and non-protein thiols (NPTs) also increased as the concentration of Cd increased.

Electric Field-Enhanced Cadmium Accumulation and Photosynthesis in a Woody Ornamental Hyperaccumulator-Lonicera japonica Thunb.

The multi-system of electro-phytotechnology using a woody ornamental cadmium (Cd) hyperaccumulator (Lonicera japonica Thunb.) is a new departure for environmental remediation. The effects of four electric field conditions on Cd accumulation, growth, and photosynthesis of L. japonica under four Cd treatments were investigated. Under 25 and 50 mg L−1 Cd treatments, Cd accumulation in L. japonica was enhanced significantly compared to the control and reached 1110.79 mg kg−1 in root and 428.67 mg kg−1 in shoots influenced by the electric field, especially at 2 V cm−1, and with higher bioaccumulation coefficient (BC), translocation factor (TF), removal efficiency (RE), and the maximum Cd uptake, indicating that 2 V cm−1 voltage may be the most suitable electric field for consolidating Cd-hyperaccumulator ability. It is accompanied by increased root and shoots biomass and photosynthetic parameters through the electric field effect. These results show that a suitable electric field may improve the growth, hyperaccumulation, and photosynthetic ability of L. japonica. Meanwhile, low Cd supply (5 mg L−1) and medium voltage (2 V cm−1) improved plant growth and photosynthetic capacity, conducive to the practical application to a plant facing low concentration Cd contamination in the real environment.

SELECTION OF CADMIUM NON-ACCUMULATING RICE GENOTYPES TO REDUCE HEALTH RISK

Cadmium (Cd) is regarded as one the most toxic heavy metals. Long term exposure to Cd via air, water, soil or food can be carcinogenic and can also lead to other bone, urinary, reproductive, cardiovascular and nervous disorders. Farmers in order to achieve high quality crops often use excess phosphorus fertilizers and in addition to this leakage of sewage sludge in the agricultural farmlands often leads to Cd contamination in agricultural fields. This holds a long term consequence because the Cd can be easily absorbed by the plants and thus Cd enters the food chain and can get accumulated in human organs. Rice is a major staple crop across the world which holds a vast genotypic variation. Different rice cultivars tends to accumulate different levels of Cd in the rice grains and hence detailed study is required to identify the rice genotypes which do not accumulate Cd in the grains so that they can be regarded as “Cdsafe” cultivars. In the present study, 58 different indica rice cultivars which are popularly grown all over India, have been grown in moderately Cd contaminated soil and results showed differential levels of Cd in the rice grains. Among 58 rice cultivars, 32 cultivars accumulated Cd in the rice grains and rest did not. The rice cultivars namely, Suma, Ranjit, Pratiksha, Kausallya, Ratna, Khitish, Mali-4, Barsha and Annada can be considered to be Cd hyperaccumulators based on the level of Cd accumulation in the rice grains.

Genome-Wide Characterization of Sedum plumbizincicola&nbsp;HMA Gene Family Provides Functional Implications in Cadmium Response.

Heavy-metal ATPase (HMA), an ancient family of transition metal pumps, plays important roles in the transmembrane transport of transition metals such as Cu, Zn, Cd, and Co. Although characterization of HMAs has been conducted in several plants, scarcely knowledge was revealed in Sedum plumbizincicola, a type of cadmium (Cd) hyperaccumulator found in Zhejiang, China. In this study, we first carried out research on genome-wide analysis of the HMA gene family in S. plumbizincicola and finally identified 8 SpHMA genes and divided them into two subfamilies according to sequence alignment and phylogenetic analysis. In addition, a structural analysis showed that SpHMAs were relatively conserved during evolution. All of the SpHMAs contained the HMA domain and the highly conserved motifs, such as DKTGT, GDGxNDxP, PxxK S/TGE, HP, and CPx/SPC. A promoter analysis showed that the majority of the SpHMA genes had cis-acting elements related to the abiotic stress response. The expression profiles showed that most SpHMAs exhibited tissue expression specificity and their expression can be regulated by different heavy metal stress. The members of Zn/Co/Cd/Pb subgroup (SpHMA1-3) were verified to be upregulated in various tissues when exposed to CdCl2. Here we also found that the expression of SpHMA7, which belonged to the Cu/Ag subgroup, had an upregulated trend in Cd stress. Overexpression of SpHMA7 in transgenic yeast indicated an improved sensitivity to Cd. These results provide insights into the evolutionary processes and potential functions of the HMA gene family in S. plumbizincicola, laying a theoretical basis for further studies on figuring out their roles in regulating plant responses to biotic/abiotic stresses.

Tolerance mechanism and phytoremediation potential of Pistia stratiotes to zinc and cadmium co-contamination

Pistia stratiotes can not only effectively remediate eutrophic water, but also displays strong absorption and bioaccumulation abilities for heavy metals. However, it has not been well-understood how the plant resists the combined stress of heavy metals. In these experiments, the morphophysiological traits, the ascorbate-glutathione (AsA-GSH) cycle, the glyoxalase system, and the contents of zinc (Zn) and cadmium (Cd) were investigated under Zn and Cd co-pollution. The AsA-GSH cycle and glyoxalase system could coordinately alleviate the oxidative and carbonyl stress, which was identified as an important tolerance mechanism. With Zn50Cd1, Zn50Cd10, Zn100Cd1, and Zn100Cd10 treatments for 18 days, 90.75–93.69% of Zn and 88.13–96.96% Cd accumulated in the roots. Treatments with Zn50Cd50, and Zn100Cd50 for 18 days resulted in a decrease of stress tolerance and chlorophyll content in leaves, an increase in plasma membrane permeability, a massive accumulation of methylglyoxal (MG), and visible toxic symptoms. Additionally, the bioaccumulation factor (BCF) for roots and shoots and the translocation factor (TF) were >1, and the content of Cd in shoots was no <100 mg·kg−1. This indicated P. stratiotes was a Cd hyperaccumulator and have great potential for the phytoremediation of heavy metal contaminated water. Novelty statement Pistia stratiotes, a cadmium hyperaccumulator, has great application potential for the phytoremediation of zinc and cadmium co-polluted water.