Cadmium absorption and transportation pathways in plants

Phytoremediation of Cadmium Polluted Soils: Current Status and Approaches for Enhancing

Cadmium (Cd) is a heavy metal present in atmosphere, rocks, sediments, and soils without a known role in plants. It is relatively mobile and can easily enter from soil into groundwater and contaminate the food chain. Its presence in food in excess amounts may cause severe conditions in humans, therefore prevention of cadmium entering the food chain and its removal from contaminated soils are important steps in preserving public health. In the last several years, several approaches for Cd remediation have been proposed, such as the use of soil amendments or biological systems for reduction of Cd contamination. One of the approaches is phytoremediation, which involves the use of plants for soil clean-up. In this review we summarized current data on the use of different plants in phytoremediation of Cd as well as information about different approaches which have been used to enhance phytoremediation. This includes data on the increasing metal bioavailability in the soil, plant biomass, and plant accumulation capacity as well as seed priming as a promising novel approach for phytoremediation enhancing.

Mechanism of cadmium tolerance in Salicornia europaea at optimum levels of NaCl

Many saline-alkali soils around the world are polluted by the heavy metal Cd, restricting the development of agriculture and ecology in those regions. The halophyte Salicornia europaea L. is capable of growing healthily in Cd-contaminated saline-alkali soil, suggesting that the species is tolerant to stress caused by both salt and heavy metals. In this study, the mechanism of Cd tolerance in this species was explored under 200 mM NaCl. Flame spectrophotometric assays for ions content and spectrophotometric for organic soluble substances, antioxidant enzyme activity, phytochelatins (PCs) content and phytochelatin synthase (PCS) activity, the photosynthetic parameters by portable photosynthesis measurement system, genes expression by qRT-PCR analysis were carried out. Cd treatment significantly decreased the dry weight, photosynthetic rate, K⁺ , Zn²⁺ , and Fe^2+/3+ content, while significantly increasing Na⁺ and Cd⁺ , soluble organic matter, and reactive oxygen species (ROS) levels. Compared with Cd treatment at 0 mM NaCl, Cd treatment at 200 mM NaCl significantly increased dry weight and photosynthetic rate while significantly decreasing ROS content through increased antioxidant enzyme activity. When exposed to Cd stress, treatment with 200 mM NaCl significantly increased PCs content and PCS activity and up-regulated the expression of the phytochelatin synthase genes CDA1 and PCS1 were, thereby increasing resistance to Cd. NaCl treatment increases the tolerance of S. europaea to the heavy metal Cd by growing rapidly, reducing the quantity of Cd²⁺ from entering the plant shoots, increasing the levels of PCs that chelate Cd²⁺ , thereby reducing its toxicity.

Quantitative proteome analysis reveals changes of membrane transport proteins in Sedum plumbizincicola under cadmium stress

Sedum plumbizincicola is an herbaceous species tolerant of excessive cadmium accumulation in above-ground tissues. The implications of membrane proteins, especially integrative membrane proteins, in Cd detoxification of plants have received attention in recent years, but a comprehensive profiling of Cd-responsive membrane proteins from Cd hyperaccumulator plants is lacking. In this study, the membrane proteins of root, stem, and leaf tissues of S. plumbizincicola seedlings treated with Cd solution for 0, 1 or 4 days were analyzed by Tandem Mass Tag (TMT) labeling-based proteome quantification (Data are available via ProteomeXchange with identifier PXD025302). Total 3353 proteins with predicted transmembrane helices were identified and quantified in at least one tissue group. 1667 proteins were defined as DAPs (differentially abundant proteins) using fold change >1.5 with p-values <0.05. The number of DAPs involved in metabolism, transport protein, and signal transduction was significantly increased after exposure to Cd, suggesting that the synthesis and decomposition of organic compounds and the transport of ions were actively involved in the Cd tolerance process. The number of up-regulated transport proteins increased significantly from 1-day exposure to 4-day exposure, from 5 to 112, 16 to 42, 18 to 44, in root, stem, and leaf, respectively. Total 352 Cd-regulated transport proteins were identified, including ABC transporters, ion transport proteins, aquaporins, proton pumps, and organic transport proteins. Heterologous expression of SpABCB28, SpMTP5, SpNRAMP5, and SpHMA2 in yeast and subcellular localization showed the Cd-specific transport activity. The results will enhance our understanding of the molecular mechanism of Cd hypertolerance and hyperaccumulation in S. plumbizincicola and will be benefit for future genetic engineering in phytoremediation.

Rootstock-Mediated Genetic Variance in Cadmium Uptake by Juvenile Cacao (Theobroma cacao L.) Genotypes, and Its Effect on Growth and Physiology

Grafting typically offers a shortcut to breed tree orchards throughout a multidimensional space of traits. Despite an overwhelming spectrum of rootstock-mediated effects on scion traits observed across several species, the exact nature and mechanisms underlying the rootstock-mediated effects on scion traits in cacao (Theobroma cacao L.) plants often remain overlooked. Therefore, we aimed to explicitly quantify rootstock-mediated genetic contributions in recombinant juvenile cacao plants across target traits, specifically cadmium (Cd) uptake, and its correlation with growth and physiological traits. Content of chloroplast pigments, fluorescence of chlorophyll a, leaf gas exchange, nutrient uptake, and plant biomass were examined across ungrafted saplings and target rootstock × scion combinations in soils with contrasting levels of Cd. This panel considered a total of 320 progenies from open-pollinated half-sib families and reciprocal full-sib progenies (derived from controlled crosses between the reference genotypes IMC67 and PA121). Both family types were used as rootstocks in grafts with two commercial clones (ICS95 and CCN51) commonly grown in Colombia. A pedigree-based best linear unbiased prediction (A-BLUP) mixed model was implemented to quantify rootstock-mediated narrow-sense heritability (h 2) for target traits. A Cd effect measured on rootstocks before grafting was observed in plant biomass, nutrient uptake, and content of chloroplast pigments. After grafting, damage to the Photosystem II (PSII) was also evident in some rootstock × scion combinations. Differences in the specific combining ability for Cd uptake were mostly detected in ungrafted rootstocks, or 2 months after grafting with the clonal CCN51 scion. Moderate rootstock effects (h 2> 0.1) were detected before grafting for five growth traits, four nutrient uptake properties, and chlorophylls and carotenoids content (h 2 = 0.19, 95% CI 0.05-0.61, r = 0.7). Such rootstock effects faded (h 2< 0.1) when rootstock genotypes were examined in soils without Cd, or 4 months after grafting. These results suggest a pervasive genetic conflict between the rootstock and the scion genotypes, involving the triple rootstock × scion × soil interaction when it refers to Cd and nutrient uptake, early growth, and photosynthetic process in juvenile cacao plants. Overall, deepening on these findings will harness early breeding schemes of cacao rootstock genotypes compatible with commercial clonal scions and adapted to soils enriched with toxic levels of Cd.

Transcriptome analysis and physiological indicators reveal the role of sulfur in cadmium accumulation and transportation in water spinach (Ipomoea aquatica Forsk.)

Cadmium (Cd) contamination of croplands has become a threat to crop food safety and human health. In this study, we investigated the effect of sulfur on the growth of water spinach under Cd stress and the amount of Cd accumulation by increasing the soil sulfate content. We found that the biomass of water spinach significantly increased after the application of sulfur while the shoot Cd concentration was considerably reduced (by 31%). The results revealed that sulfur could promote the expression of PME and LAC genes, accompanied by an increase in PME activity and lignin content. Also, the cell wall Cd content of water spinach roots was significantly increased under sulfur treatment. This finding suggests that sulfur could enhance the adsorption capacity of Cd by promoting the generation of cell wall components, thereby inhibiting the transportation of Cd via the apoplastic pathway. In addition, the higher expression of Nramp5 under the Cd1S0 (concentration of Cd and sulfur are 2.58 and 101.31 mg/kg respectively) treatment led to increased Cd uptake. The CAX3 and ABC transporters and GST were expressed at higher levels along with a higher cysteine content and GSH/GSSR value under Cd1S1 (concentration of Cd and sulfur are 2.60 and 198.36 mg/kg respectively) treatment, which contribute to the Cd detoxification and promotion of Cd compartmentalization in root vacuoles, thereby reducing the translocation of Cd to the shoot via the symplastic pathway.

Cadmium affects cell niches maintenance in Arabidopsis thaliana post-embryonic shoot and root apical meristem by altering the expression of WUS/WOX homolog genes and cytokinin accumulation

Cadmium (Cd) is one of the most widespread polluting heavy metals in both terrestrial and aquatic environments and represents an extremely significant pollutant causing severe environmental and social problems due to its high toxicity and large solubility in water. In plants, the root is the first organ that get in contact with Cd. It is absorbed by the root system and translocated to the shoot and leaves through xylem loading, causing a variety of genetic, biochemical, and physiological damages. Cd inhibits both the root and shoot growth, but the mechanisms underlying this inhibition remain elusive. In this context in the present work we focused the attention on the effects of Cd on meristem size and organization of both shoot and root. To this aim morpho-histological and molecular analyses were carried out on 5 days old seedlings exposed or not to Cd (100 μM and 150 μM for 24) of wild type and transgenic lines expressing molecular markers with an important role in shoot and root pattern organization. More precisely, we monitored the expression pattern of WUS/CLV3 and WOX5 transcription factors involved in the establishment and maintenance of stem cell niche and the control of meristem size and of TCSn::GFP cytokinin-sensitive sensor as relevant components of hormone circuit controlling shoot and root growth. The results highlighted that the treatments with Cd impacts shoot and root size and shape by altering the paralogous WOX genes expression via cytokinin accumulation.

Ammonium-nitrogen addition at the seedling stage does not reduce grain cadmium concentration in two common wheat (Triticum aestivum L.) cultivars

High cadmium (Cd) concentration in common wheat (Triticum aestivum L.) grains poses potential health risks. Several management strategies have been used to reduce grain Cd concentration. However, limited information is available on the use of ammonium-nitrogen (NH₄⁺-N) as a strategy to manage Cd concentration in wheat grains. In this study, NH₄⁺-N addition at the seedling stage unchanged the grain Cd concentration in the high-Cd accumulator, Zhoumai 18 (ZM18), but dramatically increased that in the low-Cd accumulator, Yunmai 51 (YM51). Further analysis revealed that the effects of NH₄⁺-N addition on whole-plant Cd absorption, root-to-shoot Cd translocation, and shoot-to-grain Cd remobilization were different between the two wheat cultivars. In ZM18, NH₄⁺-N addition did not change whole-plant Cd absorption, but inhibited root-to-shoot Cd translocation and Cd remobilization from lower internodes, lower leaves, node 1, and internode 1 to grains via the down-regulation of yellow stripe-like transporters (YSL), zinc transporters (ZIP5, ZIP7, and ZIP10), and heavy-metal transporting ATPases (HMA2). This inhibition decreased the grain Cd content by 29.62%, which was consistent with the decrease of the grain dry weight by 23.26%, leading to unchanged grain Cd concentration in ZM18. However, in YM51, NH₄⁺-N addition promoted continuous Cd absorption during grain filling, root-to-shoot Cd translocation and whole-plant Cd absorption. The absorbed Cd was directly transported to internode 1 via the xylem and then re-transported to grains via the phloem by up-regulated YSL, ZIP5, and copper transporters (COPT4). This promotion increased the grain Cd content by 245.35%, which was higher than the increased grain dry weight by 132.89%, leading to increased grain Cd concentration in YM51. Our findings concluded that the addition of NH₄⁺-N fertilizer at the seedling stage is not suitable for reducing grain Cd concentration in common wheat cultivars.

Unraveling the mechanisms controlling Cd accumulation and Cd-tolerance in Brachiaria decumbens and Panicum maximum under summer and winter weather conditions

We evaluated the mechanisms that control Cd accumulation and distribution, and the mechanisms that protect the photosynthetic apparatus of Brachiaria decumbens Stapf. cv. Basilisk and Panicum maximum Jacq. cv. Massai from Cd-induced oxidative stress, as well as the effects of simulated summer or winter conditions on these mechanisms. Both grasses were grown in unpolluted and Cd-polluted Oxisol (0.63 and 3.6 mg Cd kg^-1 soil, respectively) at summer and winter conditions. Grasses grown in the Cd-polluted Oxisol presented higher Cd concentration in their tissues in the winter conditions, but the shoot biomass production of both grasses was not affected by the experimental conditions. Cadmium was more accumulated in the root apoplast than the root symplast, contributing to increase the diameter and cell layers of the cambial region of both grasses. Roots of B. decumbens were more susceptible to disturbed nutrients uptake and nitrogen metabolism than roots of P. maximum. Both grasses translocated high amounts of Cd to their shoots resulting in oxidative stress. Oxidative stress in the leaves of both grasses was higher in summer than winter, but only in P. maximum superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were increased. However, CO₂ assimilation was not affected due to the protection provided by reduced glutathione (GSH) and phytochelatins (PCs) that were more synthesized in shoots than roots. In summary, the root apoplast was not sufficiently effective to prevent Cd translocation from roots to shoot, but GSH and PCs provided good protection for the photosynthetic apparatus of both grasses.

Uptake, accumulation and elimination of cadmium in a soil - Faba bean (Vicia faba) - Aphid (Aphis fabae) - Ladybird (Coccinella transversalis) food chain

Cadmium is a highly mobile toxic heavy metal and a serious hazard to the biosphere. We studied uptake, accumulation and elimination of cadmium in a soil - faba bean - aphid - ladybird food chain. The soil in the study was amended with Cd at concentrations 0, 5, 10, 20 and, 30 mg kg^-1 (w/w). We noted significant Cd transfer in a dose-dependent manner. Cadmium biomagnified in faba bean roots and aphids while biominimized in ladybirds as revealed by their respective transfer coefficients. The concentration-dependent removal of Cd from aphids through excretion via honeydew as well as through pupal exuviae of ladybirds during metamorphosis links to possible mechanisms of Cd detoxification at these trophic levels, which regulates the bioaccumulation of Cd along the food chain. These findings press for the advance studies to find and understand the physiological pathways and mechanisms leading to bio-minimization of Cd across the food chain.

Polyaspartic acid alleviates cadmium toxicity in rapeseed leaves by affecting cadmium translocation and cell wall fixation of cadmium

Polyaspartic acid (PASP) is a macromolecule compound with carboxylic acid side chains which is polymerized by L-aspartic acid, has been used as a biodegradable and environmentally-friendly chelating agent to enhance the phytoremediation of heavy metal-contaminated soils. Cadmium (Cd) is a toxic element for plant growth, productivity, and food security. To reveal the responses of PASP to plant physiology and morphology under Cd stress, we comprehensively analyzed soil characteristics, cell ultrastructure, reactive oxygen species (ROS), antioxidant enzymes, Cd uptake, transport, subcellular distribution, cell wall compositions, and their Cd chelating capacity in rapeseed. The results showed PASP increased the content of total N, total P, and available P in soil by 3.4%, 28.6%, and 39.8%, respectively, but did not change soil pH and available Cd. Meanwhile, PASP promoted dry mass accumulation and increased photosynthetic pigment content in rapeseed leaves by maintaining the chloroplast structure. Lower malondialdehyde (MDA) content and hydrogen peroxide (H2O2) accumulation and activated antioxidant enzymes in leaves indicate that PASP contributed to relieving Cd-induced oxidative damage to cells of rapeseed leaves. The results indicated that PASP application increased the Cd distribution ratio in root cell walls from 47.4% to 62.3% and decreased the Cd content in xylem sap by 37.8%, which ultimately reduced Cd reallocation in leaves. Additionally, higher pectin content and Cd in pectin resulted in higher Cd retention in leaf cell walls while reducing its concentration in the organelle fraction. The results indicated that 0.3% PASP effectively alleviated Cd stress in rapeseed leaves by inhibiting Cd transportation from roots, activating antioxidant enzymes to scavenge ROS, and promoting Cd chelation by cell wall pectin in leaves.

Impacts of heavy metals and medicinal crops on ecological systems, environmental pollution, cultivation, and production processes in China

Heavy metals are widely distributed in the environment due to the natural processes and anthropogenic human activities. Their migration into no contaminated areas contributing towards pollution of the ecosystems e.g. soils, plants, water and air. It is recognized that heavy metals due to their toxicity, long persistence in nature can accumulate in the trophic chain and cause organism dysfunction. Although the popularity of herbal medicine is rapidly increasing all over the world heavy metal toxicity has a great impact and importance on herbal plants and consequently affects the quality of herbal raw materials, herbal extracts, the safety and marketability of drugs. Effective control of heavy metal content in herbal plants using in pharmaceutical and food industries has become indispensable. Therefore, this review describes various important factors such as ecological and environmental pollution, cultivation and harvest of herbal plants and manufacturing processes which effects on the quality of herbal plants and then on Chinese herbal medicines which influence human health. This review also proposes possible management strategies to recover environmental sustainability and medication safety. About 276 published studies (1988-2021) are reviewed in this paper.

Uptake of microplastics by carrots in presence of As (III): Combined toxic effects

Current research on the migration of microplastics into plants is in its most important phase; however, there is no such research on root vegetables, even though the edible parts of root vegetables are in direct contact with microplastics. Considering arsenic (As)-containing groundwater used in hydroponics and the degradation of plastic materials in hydroponic facilities, we investigated the impacts of As and polystyrene (PS) microplastics on carrot growth. We found that PS microplastics sized 1 µm can enter carrot roots and accumulate in the intercellular layer but are unable to enter the cells; those sized 0.2 µm can migrate to the leaves. Larger microplastics can enter the roots (PS particles sized 1219.7 nm) and leaves (607.2 nm) in presence of As (III). Gaussian analysis shows that As increases the negatively charged area of PS and causes a greater amount of microplastics to enter the carrot. As also causes cell walls to distort and deform, allowing PS particles (< 200 nm) to enter the cells. PS and 4 mg L^-1 As can induce oxidative bursts in carrot tissue, reducing the carrot quality. Moreover, As exacerbates the effect of PS on carrots. Molecular docking results show that the presence of PS in carrots destroys the tertiary structure of pectin methyl esterase and causes carrots to lose their crispness. These findings indicate that plastic material in hydroponic facilities can be leached to crops. Microplastics produced by the degradation of such materials not only reduce the nutritional value of carrots, leading to economic losses, but also pose potential risks to human health. The presence of As in the hydroponic solution results in more PS entering the carrot tissue and even the cells, bringing greater health threats for the consumers.

Responses to Cadmium in Early-Diverging Streptophytes (Charophytes and Bryophytes): Current Views and Potential Applications

Several transition metals are essential for plant growth and development, as they are involved in various fundamental metabolic functions. By contrast, cadmium (Cd) is a metal that can prove extremely toxic for plants and other organisms in a dose-dependent manner. Charophytes and bryophytes are early-diverging streptophytes widely employed for biomonitoring purposes, as they are able to cope with high concentrations of toxic metal(loid)s without showing any apparent heavy damage. In this review, we will deal with different mechanisms that charophytes and bryophytes have evolved to respond to Cd at a cellular level. Particular attention will be addressed to strategies involving Cd vacuolar sequestration and cell wall immobilization, focusing on specific mechanisms that help achieve detoxification. Understanding the effects of metal(loid) pollution and accumulation on the morpho-physiological traits of charophytes and bryophytes can be in fact fundamental for optimizing their use as phytomonitors and/or phytoremediators.

Cadmium-induced phytotoxicity and tolerance response in the low-Cd accumulator of Chinese cabbage (Brassica pekinensis L.) seedlings

In vegetable production, Chinese cabbage can readily accumulate cadmium (Cd) into its edible parts and exceed food safety standards. However, there are still some ecotypes that respond differently to cadmium stress. This study aimed to investigate the differences of Cd-induced (0, 10, 50, 100, 200 µM) response under hydroponic culture between two Chinese cabbage ecotypes which were promoted in northeastern China from the characteristics of biomass, uptake kinetic, accumulation, and initial oxidative stress. In this paper, it was confirmed that Jinfeng (JF) was a Cd-tolerant cultivar and had low Cd accumulation in edible part, while Qiutian (QT) was Cd-sensitive, exhibiting a faster Cd uptake rate but lacking effective Cd detoxication mechanisms, and was severely damaged by 10 µM Cd treatment. Conversely, even at a high Cd concentration of 200 µM, Jinfeng had weaker biomass inhibition, lower root Cd affinity, more difficult root-to-leaf translocation, and stronger antioxidant enzyme activity than Qiutian. In conclusion, Jinfeng can endure mild Cd stress (<10 µM), and Qiutian can be used as a Cd indicator. This study provides reliable materials and related data support for vegetable production in areas with mild Cd pollution.Novelty statement: This work further investigates the unique features of low-Cd accumulator in Chinese cabbage (Brassica pekinensis L.) seedlings as an interesting material for vegetable production in areas with mild Cd pollution. It also explains the differences between Cd-tolerant and Cd-sensitive cultivars under different cadmium stress levels and how these differences can alter their response. With the increase of Cd concentration, Cd-tolerant cultivars compared to Cd-sensitive cultivars showed less biomass decrease, lower accumulation, lower TF, more chemically stable Cd in roots and more active antioxidant enzymes under the same Cd stress level. With the development of seedlings, the uptake of Cd in roots and the translocation to the leaves were effectively restricted by the poor Cd affinity of roots, the conversion of Cd chemical forms and the promotion of antioxidase activities, in a Cd-tolerant low accumulator, Jinfeng.

Biochemical metabolism of young plants of Ucuúba (Virola surinamensis) in the presence of cadmium

Virola surinamensis is a forest species widely distributed in the estuaries of the Amazon. These ecosystems are susceptible to contamination by Cadmium (Cd), indicating that the plant has strategies for tolerating this metal. The aim of this study was to assess the nitrogen and carbon metabolism of young plants of Ucuúba (Virola surinamensis) in the presence of cadmium with the perspective of the phytoremediation of contaminated environments. The used experimental design was a completely randomized design with five Cd concentrations (0, 15, 30, 45, and 60 mg L^- 1), for 60 days. In general, Cd did not affect nitrate concentration in the root but had a positive effect on leaves. The reduction of nitrate reductase (NR) in plants exposed to Cd was followed by a decrease in ammonia, total soluble amino acids (TSA), and total soluble proteins (TSP). Cd promoted an increase in the concentration of total soluble carbohydrates (TSC), proline, sucrose, and reducing sugars in the plants. The increase in TSC, sucrose and proline, suggests a metabolic regulatory mechanism of V. surinamensis against Cd stress.

Cadmium toxicity in plants: Impacts and remediation strategies

Cadmium (Cd) is an unessential trace element in plants that is ubiquitous in the environment. Anthropogenic activities such as disposal of urban refuse, smelting, mining, metal manufacturing, and application of synthetic phosphate fertilizers enhance the concentration of Cd in the environment and are carcinogenic to human health. In this manuscript, we reviewed the sources of Cd contamination to the environment, soil factors affecting the Cd uptake, the dynamics of Cd in the soil rhizosphere, uptake mechanisms, translocation, and toxicity of Cd in plants. In crop plants, the toxicity of Cd reduces uptake and translocation of nutrients and water, increases oxidative damage, disrupts plant metabolism, and inhibits plant morphology and physiology. In addition, the defense mechanism in plants against Cd toxicity and potential remediation strategies, including the use of biochar, minerals nutrients, compost, organic manure, growth regulators, and hormones, and application of phytoremediation, bioremediation, and chemical methods are also highlighted in this review. This manuscript may help to determine the ecological importance of Cd stress in interdisciplinary studies and essential remediation strategies to overcome the contamination of Cd in agricultural soils.

Cadmium (II)-Induced Oxidative Stress Results in Replication Stress and Epigenetic Modifications in Root Meristem Cell Nuclei of Vicia faba

Among heavy metals, cadmium is considered one of the most toxic and dangerous environmental factors, contributing to stress by disturbing the delicate balance between production and scavenging of reactive oxygen species (ROS). To explore possible relationships and linkages between Cd(II)-induced oxidative stress and the consequent damage at the genomic level (followed by DNA replication stress), root apical meristem (RAM) cells in broad bean (V. faba) seedlings exposed to CdCl₂ treatment and to post-cadmium recovery water incubations were tested with respect to H₂O₂ production, DNA double-strand breaks (γ-phosphorylation of H2AX histones), chromatin morphology, histone H3S10 phosphorylation on serine (a marker of chromatin condensation), mitotic activity, and EdU staining (to quantify cells typical of different stages of nuclear DNA replication). In order to evaluate Cd(II)-mediated epigenetic changes involved in transcription and in the assembly of nucleosomes during the S-phase of the cell cycle, the acetylation of histone H3 on lysine 5 (H3K56Ac) was investigated by immunofluorescence. Cellular responses to cadmium (II) toxicity seem to be composed of a series of interlinked biochemical reactions, which, via generation of ROS and DNA damage-induced replication stress, ultimately activate signal factors engaged in cell cycle control pathways, DNA repair systems, and epigenetic adaptations.

Boron supply alleviates cadmium toxicity in rice (Oryza sativa L.) by enhancing cadmium adsorption on cell wall and triggering antioxidant defense system in roots

Cadmium (Cd) pollution is a key concern globally that affects plant growth and productivity. Boron (B) is a micronutrient that helps in the formation of the primary cell wall (CW) and alleviates negative effects of toxic elements on plant growth. Nonetheless, knowledge about how B can reduce Cd toxicity in rice seedlings is not enough, particularly regarding CW-Cd adsorption. Therefore, the current experiment investigated the alleviative role of B on Cd toxicity in rice seedling. The experiment was carried out with 0 μM and 30 μM H₃BO₃ under 50 μM Cd toxicity in hydroponics. The results showed that Cd exposure alone inhibited plant growth parameters and caused lipid peroxidation. Moreover, Cd toxicity led to obvious visible toxicity symptoms on the leaves. However, increasing the availability of B alleviated Cd toxicity by reducing Cd concentration in plant tissues and improving antioxidative system. Moreover, cell wall pectin and hemicellulose adsorbed a significant amount of Cd. Fourier-Transform Infrared spectroscopy (FTIR) spectra exhibited that cell wall functional groups were increased by B application. Scanning electron microscopy (SEM) equipped with energy-dispersive X-ray (EDX) microanalysis confirmed the higher Cd binding onto CW. The findings of this investigation showed that B could mitigate Cd stress by decreasing Cd uptake and encouraging Cd adsorption on CW, and activation of the protective mechanisms. The present results might help to increase rice productivity on Cd polluted soils.

Regulation of As and Cd accumulation in rice by simultaneous application of lime or gypsum with Si-rich materials

Calcium (Ca) and silicon (Si) have been found to reduce inorganic pollutant accumulation by agricultural plants. Arsenic (As) and cadmium (Cd) are the most common and dangerous inorganic pollutants in cultivated soil that often present simultaneously. Due to difference in chemical properties of As and Cd, concurrent minimizing their uptake poses a problem. The effect of two types of Si fertilizers and Si-treated metallurgical slag applied with or without limestone or gypsum on the As and Cd accumulation by rice was investigated in medium-polluted paddy soils in field test. Application of Ca- and Si-rich substances reduced the grain As by 16 to 68% and the grain Cd by 30 to 56% with increasing yield by 16.6 to 31.0%. The root-to-grain transport of As and Cd depended on the plant-available Si supply in the soil. Soil-applied Si resulted in diminished As and Cd translocation inside plant tissue and decreased the pollutant mobility in the soil. The combination of Ca- and Si-rich substances reinforced the reduction in both the pollutant mobility in soil and accumulation by rice grain. Silicon-rich materials mainly impacted both As and Cd translocation into the grain, whereas Ca-rich substances demonstrated a more remarkable effect on the pollutant mobility in the soil. Limestone showed a higher decrease in the mobility of Cd, while gypsum was more efficient in the case of As. Thus, for minimizing pollutant accumulation by rice grain, the combination of Si fertilizer with limestone or gypsum could be recommended in the co-contaminated soil with prevailing Cd or As, respectively.

Progress in our understanding of plant responses to the stress of heavy metal cadmium

Heavy metal pollution is a major environmental stress affecting plant growth and development. The heavy metal cadmium inhibits various physiological processes in plants, including seed germination and seedling growth, photosynthesis, and antioxidation. Extensive research has been conducted on the toxic effects of Cd²⁺ on plants and the mechanisms of Cd²⁺ tolerance. Here, we review recent advancements in our understanding of the absorption, transport, and accumulation of Cd²⁺ in plants and the mechanisms of Cd²⁺ tolerance.

Eichhornia crassipes (Mart.) Solms (natural or carbonized) as biosorbent to remove pollutants in water

The prolific aquatic herb Eichhornia crassipes considered a pest in many countries can cause damage such as obstruction of water flows and impair the locomotion of fishing boats. However, E. crassipes is renewable, inexpensive, and widely available in nature, and its ability to adsorb recalcitrant pollutants with mutagenic and carcinogenic properties, including synthetic dyes and heavy metals, has been extensively studied by the scientific community. This review paper analyzes previous reports concerning the use of E. crassipes (in the natural and carbonized form) as an adsorbent for heavy metal cations and textile dye. The adsorptive capacity of E. crassipes, the best conditions (adsorbent dosage, pH, and temperature) for the removal of these pollutants, the mechanism of adsorption, and the comparison between natural and carbonized forms (advantages and disadvantages) are discussed. All the results revised in this review indicated that the use of E. crassipes (and its carbon derived) as adsorbent is promising and is an excellent material to be applied in the water treatment. It could be used in the actual technologies for the treatment of contaminated water by heavy metals and textile dyes; however, more studies need to be made on scale-up, economy projects, and related issues, to be finally implemented in wastewater treatment plants.

Cadmium accumulation, subcellular distribution and chemical fractionation in hydroponically grown Sesuvium portulacastrum [Aizoaceae]

Sesuvium portulacastrum is a well-known halophyte with considerable Cd accumulation and tolerance under high Cd stress. This species is also considered as a good candidate of Cd phytoremediation in the polluted soils. However, the mechanism of Cd accumulation, distribution and fractionation in different body parts still remain unknown. Seedlings of Sesuvium portulacastrum were studied hydroponically under exposure to a range of Cd concentrations (50 μM or μmol/L to 600 μM or μmol/L) for 28 days to investigate the potential accumulation capability and tolerance mechanisms of this species. Cd accumulation in roots showed that the bio-concentration factor was > 10, suggesting a strong ability to absorb and accumulate Cd. Cd fractionation in the aboveground parts showed the following order of distribution: soluble fraction > cell wall > organelle > cell membrane. In roots, soluble fraction was mostly predominant than other fractions. Cd speciation in leaves and stems was mainly contained of sodium chloride and deionised water extracted forms, suggesting a strong binding ability with pectin and protein as well as with organic acids. In the roots, inorganic form of Cd was dominant than other forms of Cd. It could be suggested that sodium chloride, deionised water and inorganic contained form of Cd are mainly responsible for the adaption of this plant in the Cd stress environment and alleviating Cd toxicity.

1Selenium supply alters the subcellular distribution and chemical forms of cadmium and the expression of transporter genes involved in cadmium uptake and translocation in winter wheat (Triticum aestivum)

BACKGROUND

Cadmium (Cd) accumulation in crops affects the yield and quality of crops and harms human health. The application of selenium (Se) can reduce the absorption and transport of Cd in winter wheat.

RESULTS

The results showed that increasing Se supply significantly decreased Cd concentration and accumulation in the shoot and root of winter wheat and the root-to-shoot translocation of Cd. Se application increased the root length, surface area and root volume but decreased the average root diameter. Increasing Se supply significantly decreased Cd concentration in the cell wall, soluble fraction and cell organelles in root and shoot. An increase in Se supply inhibited Cd distribution in the organelles of shoot and root but enhanced Cd distribution in the soluble fraction of shoot and the cell wall of root. The Se supply also decreased the proportion of active Cd (ethanol-extractable (FE) Cd and deionized water-extractable (FW) Cd) in root. In addition, the expression of TaNramp5-a, TaNramp5-b, TaHMA3-a, TaHMA3-b and TaHMA2 significantly increased with increasing Cd concentration in root, and the expression of TaNramp5-a, TaNramp5-b and TaHMA2 in root was downregulated by increasing Se supply, regardless of Se supply or Cd stress. The expression of TaHMA3-b in root was significantly downregulated by 10 μM Se at both the 5 μM and 25 μM Cd level but upregulated by 5 μM Se at the 25 μM Cd level. The expression of TaNramp5-a, TaNramp5-b, TaHMA3-a, TaHMA3-b and TaHMA2 in shoot was downregulated by increasing Se supply at 5 μM Cd level, and 5 μM Se upregulated the expression of those genes in shoot at 25 μM Cd level.

CONCLUSIONS

The results confirm that Se application limits Cd accumulation in wheat by regulating the subcellular distribution and chemical forms of Cd in winter wheat tissues, as well as the expression of TaNramp5-a, TaNramp5-b and TaHMA2 in root.

Cadmium ion-chlorophyll interaction - Examination of spectral properties and structure of the cadmium-chlorophyll complex and their relevance to photosynthesis inhibition

Chlorophyll was shown to spontaneously form a complex with cadmium, which is incorporated at the central position of the chlorophyll molecule porphyrin ring, where it replaces magnesium. The rate of complex formation depended on the ratio of Cd2+ ions to chlorophyll concentration in the solution. In solutions with chlorophyll concentration of C = 1 × 10^-5 M and Cd²⁺ concentrations of C = 1 × 10^-5 M, C = 1 × 10^-3 M and C = 9 × 10^-3 M, Cd-Chl complex formation was completed after 200 h, 50 h and 33 h, respectively. The formation of Cd-Chl complex followed the second order over all substrates reaction order, first order over Cd²⁺ concentration and first over Chl concentration. The pseudo second order reaction rate constant k, when Cd²⁺ concentration was equal Chl concentration have been obtained as k = 1.510 ± 0.023 × 10^-4 M^-1min^-1. Quantum chemistry computations showed that Cd-chlorophyll complex existed in two conformations in the methanol solution with cadmium ion placed either below or above the coordination plane. Two times smaller overlap integral of the Chl fluorescence spectrum with the Cd-Chl absorption spectrum I_Chl,Cd-Chl= 2.4223 × 10^-13 cm³/M in comparison with the overlap integral of the Chl fluorescence spectrum with the Chl absorption spectrum I_Chl,Chl= 4.6210 × 10^-13 cm³/M (twice lower probability of energy transfer Chl∗ → Cd-Chl than Chl∗ → Chl) and lower Förster critical distance for resonance energy transfer: R_{oChl→Cd-Chl}= 46.773 Å, R_oChl→Chl= 52.086 Å, indicated that in plants intoxicated with cadmium, taken up from the contaminated soil, the energy transfer between Chl and Cd-Chl in antennas will be disturbed, which may be one of the reasons for the inhibition of photosynthesis.

Chemical speciation and distribution of potentially toxic elements in soilless cultivation of cucumber with sewage sludge biochar addition

Potentially toxic elements in municipal sewage sludge can be effectively immobilized during biochar production via pyrolysis. However, the bioavailability of these elements when biochar is applied in soilless cultivation to improve substrate quality has yet to be sufficiently established. In this study, we investigated the chemical speciation and cucumber plant uptake of potentially toxic elements in soilless cultivation when the growth substrate was amended with sewage sludge biochar (0, 5, 10, 15, and 20 wt%). It was found that the addition of 10 wt% biochar was optimal with respect to obtaining a high cucumber biomass and achieving low environmental risk considering the occurrence of hormesis. When the substrate was amended with 10 wt% biochar, cucumber fruit contained lower concentrations of As, Cr, and Zn and smaller bioavailable fractions of As, Cd, Cr, Ni, Cu, and Zn compared with the fruit of control plants, thereby meeting national safety requirements (standard GB 2762-2012, China). Most of the As and Cd taken up by cucumbers accumulated in the leaves and fruit, whereas Cr was found primarily in the roots, and most Ni, Cu, and Zn was detected in the fruit. Importantly, only small proportions of the potentially toxic elements in biochar were taken up by cucumber plants (As: 0.0075%; Cd: 0.038%; Ni: 0.0064%; Cu: 0.0016%; and Zn: 0.0015%). Given that the As, Cd, Ni, and Zn speciation in sewage sludge biochar was effectively immobilized after cultivation, the findings of this study indicate that sewage sludge biochar is a suitable substrate amendment in terms of the risk posed by potentially toxic elements.

Selenium enhances iron plaque formation by elevating the radial oxygen loss of roots to reduce cadmium accumulation in rice (Oryza sativa L.)

The inhibition of cadmium (Cd) absorption by selenium (Se) in rice may be associated with iron plaque (IP) formation, but the driving mechanisms are still unclear. This study investigated the effects of Se on the growth, oxidative toxicity, radial oxygen loss (ROL), IP formation, and Cd absorption of rice exposed to Cd. The results of this study showed that Cd stress elevated the levels of O₂- and H₂O₂ and depressed superoxide dismutase (SOD) and catalase (CAT) activities. The maximum ROL and IP were reduced by 43.3 % and 74.5 %, respectively. However, Se alleviated Cd toxicity by stimulating SOD and CAT activities by scavenging O₂- and H₂O₂ and enhancing the ROL profiles. Under culture conditions without Fe²⁺, Se had no impact on the total Cd levels in rice (T_Cd). However, with the addition of Fe²⁺, T_Cd was significantly reduced by 23.3 % due to the enhancement of IP formation by Se. These results indicated that Se can reduce Cd accumulation in rice in the presence of Fe²⁺ treatments. However, Se just alleviated Cd toxicity in the absence of Fe²⁺ treatments. The enhancement of ROL was a potential reason for the elevated IP formation induced by Se.

Mechanisms of low cadmium accumulation in storage root of sweetpotato (Ipomoea batatas L.)

Sweetpotato (Ipomoea batatas L.) possess great application prospects due to their low cadmium (Cd) concentration within their storage roots despite growth on Cd-polluted fields. The mechanisms of low Cd accumulation in storage root is not entirely clear. We found that the blocking effect of Cd uptake in the root absorption system and the characteristics of Cd distribution in storage root play a decisive role in the regulation of low Cd accumulation in storage root. Cd absorbed from the rhizosphere mainly accumulated in feeder roots in Cd dose-dependent accumulation analyses. Meanwhile, we found that Cd absorbed by the peels of storage root was mainly transported from peels to shoots, rather than directly into the fleshed storage root. Further analysis indicated that Cd uptake, transport, and distribution in sweetpotato hinges on whether Cd enters the plant plasma membrane by either the symplast or apoplast pathway. The Cd concentration in feeder root decreased after respiratory inhibitors CCCP and DNP treatment and increased after the culture temperature was raised from 28 ℃ to 35 ℃. Non-invasive microelectrode Cd flux measurements further revealed that Cd uptake in feeder root was affected greatly by the Cd concentration of the solution and was markedly reduced by respiratory inhibitor CCCP. Relative to the elongation zone and mature zone, the meristematic zone was the main site of Cd uptake in the root absorption system. This study suggests that inhibition of Cd uptake by the root absorption system and the characteristics of Cd distribution in storage root are the main reasons for low cadmium accumulation in storage root.

Response of Corchorus olitorius Leafy Vegetable to Cadmium in the Soil

Corchorus olitorius, a leafy vegetable with high nutrient content, is normally collected from the wild, in areas that are prone to cadmium (Cd) toxicity. However, studies on how Cd accumulation affects vegetative and reproductive traits of leafy vegetables in South Africa are limited. Therefore, this study tested the effect of Cd accumulation on C. olitorius morphological traits. Plants were grown under various Cd concentrations and studied for variation in vegetative and reproductive traits as well as accumulation in roots and shoots. Plants exposed to 5 mg/kg Cd had longer roots with higher moisture content, heavier fresh and dried stems, as well as dried leaves, which indicated a hormetic effect in C. olitorius after exposure to low Cd concentration in the soil. Again, plants treated with 5–10 mg/kg Cd, accumulated toxic (>10 mg/kg dry weight) Cd within shoots and roots, with minor morphological alterations. Plants could survive, with some morphological defects, Cd toxicity up to 20 mg/kg in soil. Only plants exposed to 5 mg/kg could reproduce. Cd accumulation increased with an increase in the soil, with higher accumulation in shoots. The translocation factor was high (>1) in all Cd concentrations. In conclusion, C. olitorius can accumulate toxic Cd, and yet grow and reproduce either normally or better than the control. The proposed dose of Cd that induces hormesis in C. olitorius is 5 mg/kg in the soil. Therefore, C. olitorius is suitable for phytoremediation of Cd contaminated soils, but unsafe for consumption when it grows in such areas.

Urea application enhances cadmium uptake and accumulation in Italian ryegrass

Italian ryegrass (Lolium multifolorum Lam.) has a potential phytoextraction capacity for cadmium (Cd), which is considered as the most toxic heavy metal (HM) pollutant in the farmland. The promotion effect of urea application on Italian ryegrass growth has been clarified, while it is not clear whether and how urea application affects Cd accumulation in Italian ryegrass under Cd stress. A 2-year pot experiment was conducted to investigate the effect of urea application on Cd accumulation and related mechanisms by uptake inhibition and kinetics experiments. The results showed that both shoot biomass and Cd concentration under Cd stress were increased by up to 213.37% and 84.74% in 2016 and 38.15% and 47.11% in 2017 after urea application, respectively. The shoot Cd accumulation reached maximum value (910.23 and 630.09 μg pot-1 in 2016 and 2017, respectively) at the level of 300 kg ha-1 urea. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were significantly increased by urea application. Compared with control group, urea application significantly improved inhibition ratio of 2, 4-dinitrophenol (DNP) rather than LaCl3 and Ca2+. Cadmium uptake kinetics experiment showed that urea application significantly decreased the Km value and improved the α value (P < 0.01), but no significant effect on the Vmax value (P > 0.05). In conclusion, we proposed that the higher affinity to Cd2+ of the membrane transporter after urea application promoted the active uptake of Cd, which contributed to the effective Cd accumulation capacity in Italian ryegrass.

Cadmium Uptake by Wheat (Triticum aestivum L.): An Overview

Cadmium is a toxic heavy metal that may be detected in soils and plants. Wheat, as a food consumed by 60% of the world’s population, may uptake a high quantity of Cd through its roots and translocate Cd to the shoots and grains thus posing risks to human health. Therefore, we tried to explore the journey of Cd in wheat via a review of several papers. Cadmium may reach the root cells by some transporters (such as zinc-regulated transporter/iron-regulated transporter-like protein, low-affinity calcium transporters, and natural resistance-associated macrophages), and some cation channels or Cd chelates via yellow stripe 1-like proteins. In addition, some of the effective factors regarding Cd uptake into wheat, such as pH, organic matter, cation exchange capacity (CEC), Fe and Mn oxide content, and soil texture (clay content), were investigated in this paper. Increasing Fe and Mn oxide content and clay minerals may decrease the Cd uptake by plants, whereas reducing pH and CEC may increase it. In addition, the feasibility of methods to diminish Cd accumulation in wheat was studied. Amongst agronomic approaches for decreasing the uptake of Cd by wheat, using organic amendments is most effective. Using biochar might reduce the Cd accumulation in wheat grains by up to 97.8%.

Human Health Risk Assessment and Potentially Harmful Element Contents in the Cereals Cultivated on Agricultural Soils

Potentially harmful element (PHE) contents were investigated in six species of cereals in southern Poland, with human health risk implications assessed afterwards. The PHE contents belonged to the following ranges (mg/kg wet weight): As below the limit of detection ( oat (HQ = 0.38) > maize (HQ = 0.02). The total non-carcinogenic risk value of the statistical daily consumption of cereals was acceptable low (HQ = 0.58). The acceptable cancer risk (CR) level of 1.0 × 10-5 investigated only for As was not exceeded under any of the intake scenarios. Concerning the mean As content in cereals consumed daily in statistical amounts the CR value was equal to 5.1 × 10-8. The health risk value according to the Pb content in cereals using the margin of exposure (MOE) approach was equal to 1.27, indicating an acceptable low risk.

Insight into nitrogen and phosphorus enrichment on cadmium phytoextraction of hydroponically grown Salix matsudana Koidz cuttings

Cadmium (Cd) has already caused worldwide concern because of its high biotoxicity to human and plants. This study investigated how nitrogen (N) and phosphorus (P) enrichment alter the toxic morpho-physiological impacts of and accumulation of Cd in hydroponically grown Salix matsudana Koidz cuttings. Our results showed that Cd significantly depressed growth and induced a physiological response on S. matsudana cuttings, exhibiting by reduced biomass, decreased photosynthetic pigment concentrations, and increased soluble protein and peroxidase activity of shoots and roots. N and P enrichment alleviated the Cd toxic effects by increasing production of proline which prevented cuttings from damage by Cd-induced ROS, displaying with decreased malondialdehyde concentration, and stimulated overall Cd accumulation. Enrichment of N and P significantly decreased the upward Cd transfer, combing with enhanced root uptake (stimulated root activity) and retranslocation from stem, resulted in extensive Cd sequestration in S. matsudana roots. In both root and xylem, concentration of Cd is positively correlated with N and P. The improved phytoextraction potential by N and P enrichment was mainly via elevating Cd concentration in roots, probably by increased production of phytochelatins (e.g., proline) which form Cd chelates and help preventing damage from Cd-induced ROS. This study provides support for the application of S. matsudana in Cd phytoextraction even in eutrophic aquatic environments.

γ-Aminobutyric acid confers cadmium tolerance in maize plants by concerted regulation of polyamine metabolism and antioxidant defense systems

Gamma-Aminobutyric acid (GABA) accumulates in plants following exposure to heavy metals. To investigate the role of GABA in cadmium (Cd) tolerance and elucidate the underlying mechanisms, GABA (0, 25 and 50 µM) was applied to Cd-treated maize plants. Vegetative growth parameters were improved in both Cd-treated and control plants due to GABA application. Cd uptake and translocation were considerably inhibited by GABA. Antioxidant enzyme activity was enhanced in plants subjected to Cd. Concurrently GABA caused further increases in catalase and superoxide dismutase activities, which led to a significant reduction in hydrogen peroxide, superoxide anion and malondealdehyde contents under stress conditions. Polyamine biosynthesis-responsive genes, namely ornithine decarboxylase and spermidine synthase, were induced by GABA in plants grown under Cd shock. GABA suppressed polyamine oxidase, a gene related to polyamine catabolism, when plants were exposed to Cd. Consequently, different forms of polyamines were elevated in Cd-exposed plants following GABA application. The maximum quantum efficiency of photosystem II (Fv/Fm) was decreased by Cd-exposed plants, but was completely restored by GABA to the same value in the control. These results suggest a multifaceted contribution of GABA, through regulation of Cd uptake, production of reactive oxygen species and polyamine metabolism, in response to Cd stress.

Hydrogen sulphide partly involves in thiamine-induced tolerance to cadmium toxicity in strawberry (Fragaria x ananassa Duch) plants

Although thiamine (THI) and hydrogen sulphide (H₂S) both have widely been tested in the plant under stress conditions, cross talk between THI and H₂S in the acquisition of cadmium (Cd) stress tolerance needs to be studied. So, an experiment was designed to study the participation of endogenous H₂S in THI-induced tolerance to Cd stress in strawberry plants. A foliar spray solution containing THI (50 mg L^-1) was sprayed once a week for 4 weeks to the foliage of strawberry plants under Cd stress (1.0 mM CdCl₂). The plant dry weight, total chlorophyll, maximum efficiency of PSII (F_v/F_m), leaf potassium (K⁺) and calcium (Ca²⁺) as well as leaf water potential were significantly reduced, but the proline, ascorbate (AsA), glutathione (GSH), malondialdehyde (MDA), hydrogen peroxide (H₂O₂), electron leakage (EL) and leaf Cd as well as endogenous H₂S and NO were increased by Cd stress. Application of THI alleviated the oxidative damage due to Cd stress and caused a further elevation in endogenous H₂S and NO contents. Remarkably, THI-induced Cd stress tolerance was further improved by addition of sodium hydrosulfide (0.2 mM NaHS), a H₂S donor. To get an insight whether or not H₂S involved in THI-improved tolerance to Cd toxicity in strawberry plants, an H₂S scavenger, hypotaurine (HT 0.1 mM), was supplied along with the THI and NaHS treatments. THI-improved tolerance to Cd stress was partly reversed by HT by reducing leaf H₂S and NO to the level and above of these under Cd toxicity alone, respectively. The findings evidently showed that leaf H₂S and NO together involved in induced tolerance to Cd toxicity by THI. This evidence was also proved by the partly increases in MDA and H₂O₂ and decreases in antioxidant defence enzymes such as superoxide dismutase, catalase and peroxidase as well as the plant biomass and partly enhanced leaf Cd content by exogenous applied HT along with THI.

Concentration and Risk Assessment of Potentially Toxic Elements, Lead and Cadmium, in Vegetables and Cereals Consumed in Western Iran

The concentration of cadmium (Cd) and lead (Pb) in vegetable (potatoes, onions, tomatoes, lettuce, leeks, and carrots) and cereal (wheat and rice) samples collected from Iran were investigated by a graphite furnace atomic absorption spectrophotometer. In addition, we determined the health risks due to exposure to Cd and Pb through vegetable and cereal consumption by computing the estimated daily intake, the target hazard quotient (THQ), the total THQ, and the margin of exposure. The mean concentrations of Pb in potato, onion, tomato, lettuce, leek, carrot, wheat, and rice samples were measured as 0.029 ± 0.011, 0.016 ± 0.012, 0.007 ± 0.005, 0.022 ± 0.020, 0.040 ± 0.048, 0.029 ± 0.025, 0.123 ± 0.120, and 0.097 ± 0.059 mg kg^-1 wet weight, respectively, and all were below the maximum allowable concentrations set by the European Union. The mean concentrations of Cd in potatoes, onions, tomatoes, lettuce, leeks, carrots, wheat, and rice samples were measured as 0.022 ± 0.013, 0.011 ± 0.009, 0.003 ± 0.003, 0.007 ± 0.005, 0.015 ± 0.024, 0.013 ± 0.011, 0.046 ± 0.043, and 0.049 ± 0.04 mg kg^-1 wet weight, respectively, and all were below the permissible levels established by the European Union. The corresponding values for the estimated daily intake of Cd were acceptable and lower than the provisional tolerable daily intake. The THQ and total THQ values of Cd through consumption of all vegetables and cereals were lower than 1. The margin of exposure values for Pb in samples were >1, showing no significant human health risks for both potentially toxic elements. The findings of this study indicated there is no risk associated with exposure to Pb and Cd through the intake of selected vegetables and cereals in western Iran.

Human Health Risk Assessment and Potentially Harmful Element Contents in the Fruits Cultivated in the Southern Poland

The presence of potentially harmful elements (PHEs) in popularly consumed fruits in Poland was determined by inductively coupled plasma mass spectrometry. The As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se, Sb, Tl, and Zn contents were investigated in 21 fruit species grouped as berry, pome, stone, and shell fruits. The PHE contents belonged to the following ranges (mg/kg wet weight): Cd < limit of detection (LOD)-0.116, Co < LOD-0.062, Cu < LOD-15.5, Ni < LOD-2.23, Pb < LOD-2.07, Sb < LOD-0.240, Tl < LOD-0.110, and Zn 0.37-37.7. Their concentrations exceeded the maximum allowable concentration (MAC) set by European Union regulation for Pb only. Bioconcentration coefficient (BC) values, calculated in accordance to the PHE contents in exchangeable and acid soluble forms in soil after first step of the Community Bureau of Reference (BCR) sequential extraction procedure, revealed that berry fruits had potential for accumulation of Cu, Ni, Sb, and Tl; stone fruits-Cu, Sb, and Tl; pome fruits-Cu, Ni, and Sb, and shell fruit (walnut)-Cu. Human health risk assessment associated with the intake of PHEs in fruits was evaluated in terms of daily intake rates (DIR), and carcinogenic and non-carcinogenic risk by cancer risk (CR) and hazard quotient (HQ), respectively. For Pb margin of exposure (MOE) approach was used for health risk evaluation. Daily intake rates for all PHEs were below the provisional maximum tolerable daily intake (PMTDI) values. The mean total non-carcinogenic risk values were the following: berry fruits HQ = 0.47, pome fruits HQ = 0.36, stone fruits HQ = 0.42, and shell fruits (walnut) HQ = 0.22, indicating no health hazards. The carcinogenic risk for As in walnut only under an adult intake scenario (CR = 1.98 × 10-6) was found to be above the acceptable risk level. The mean Pb health risk, according to Polish statistical intake rates, was acceptable low as the MOE value was equal to 15.7 for adults. In reference to the intake rates recommended by United States Environmental Protection Agency (USEPA), MOE values for Pb indicated acceptable low risk both for adults (MOE = 14.0) and children (MOE = 1.64). In general, the finding of this research revealed no health risk arising from PHE consumption with fruits for the population of Poland.

A real filed phytoremediation of multi-metals contaminated soils by selected hybrid sweet sorghum with high biomass and high accumulation ability

Heavy metal-polluted soil is obtaining increasing global concerns. The phytoremediation is a promising technology that needs further research. This study was aiming to perform a field survey to assess the restoration and accumulation potential of five hybrid sweet sorghum species with high biomass. Those sweet sorghums were planted in three sites containing different toxic levels of Zn, Pb and Cd with one local commercial sweet sorghum as contrast sample. Plants and soils were sampled for the analysis of heavy metal concentrations. BCF and TF values showed that hybrid sweet sorghum species have higher accumulation ability than local one. Five species of hybrid sweet sorghum planted in all three sites showed no obvious toxicity symptoms, and moreover, their biomass were 12-24 times higher than that of the local one, indicating their high tolerance to heavy metals. Among them, the 9312 and G38 specimens were considered as the best-performing specimens due to their high ability to accumulate multiple metals in their shoots and roots without being affected by excessive metal contents. A reasonable disposed plan for harvested sweet sorghum after phytoremediation was proposed. The harvest sweet sorghums used for industrial ethanol and densified biofuel production could combine soil remediation with creating economic benefit. Consequently, those five hybrid sweet sorghum species, especially 9312 and G38 with high biomass production, metal accumulation ability and high tolerance against metal toxicity might have great potential in phytoremediation field.

A multiomics approach reveals the pivotal role of subcellular reallocation in determining rapeseed resistance to cadmium toxicity

Oilseed rape (Brassica napus) has great potential for phytoremediation of cadmium (Cd)-polluted soils due to its large plant biomass production and strong metal accumulation. Enhanced plant Cd resistance (PCR) is a crucial prerequisite for phytoremediation through hyper-accumulation of excess Cd. However, the complexity of the allotetraploid genome of rapeseed hinders our understanding of PCR. To explore rapeseed Cd-resistance mechanisms, we examined two genotypes, 'ZS11' (Cd-resistant) and 'W10' (Cd-sensitive), that exhibit contrasting PCR while having similar tissue Cd concentrations, and characterized their different fingerprints in terms of plant morphophysiology (electron microscopy), ion abundance (inductively coupled plasma mass spectrometry), DNA variation (whole-genome resequencing), transcriptomics (high-throughput mRNA sequencing), and metabolomics (ultra-high performance liquid chromatography-mass spectrometry). Fine isolation of cell components combined with ionomics revealed that more Cd accumulated in the shoot vacuoles and root pectins of the resistant genotype than in the sensitive one. Genome and transcriptome sequencing identified numerous DNA variants and differentially expressed genes involved in pectin modification, ion binding, and compartmentalization. Transcriptomics-assisted gene co-expression networks characterized BnaCn.ABCC3 and BnaA8.PME3 as the central members involved in the determination of rapeseed PCR. High-resolution metabolic profiles revealed greater accumulation of shoot Cd chelates, and stronger biosynthesis and higher demethylation of root pectins in the resistant genotype than in the sensitive one. Our comprehensive examination using a multiomics approach has greatly improved our understanding of the role of subcellular reallocation of Cd in the determination of PCR.

Impact of nanoparticle surface charge and phosphate on the uptake of coexisting cerium oxide nanoparticles and cadmium by soybean (Glycine max. (L.) merr.)

Engineered nanoparticles (ENPs) often interact closely with coexisting environmental pollutants; however, the effect of their surface properties on such interactions in a plant system has not been examined. This study investigated the roles of ENP surface charge and growth media chemistry on the mutual effects of cerium oxide nanoparticles (CeO2NPs) and cadmium (Cd) on their plant uptake and accumulation in a hydroponic system. Soybean seedlings were exposed to five nanoparticle/Cd treatments including: 100 mg L-1 CeO2NPs(+); 100 mg L-1 CeO2NPs(-); 100 mg L-1 CeO2NPs(+) + 1 mg L-1 Cd; 100 mg L-1 CeO2NPs(-) + 1 mg L-1 Cd; and 1 mg L-1 Cd only, in the presence or absence of 15 mg L-1 phosphorous in the form of phosphate. After 4 days of exposure, concentrations of Cd and Ce in plant tissues were quantified by inductively coupled plasma-mass spectrometry. Roots exposed to CeO2NPs(+) contained 87% higher Ce than plants exposed to CeO2NPs(-). Phosphate significantly increased the root concentration of Ce by 61% and 66% exposed to CeO2NPs(+) and CeO2NPs(-), respectively. The mutual effect of CeO2NPs and Cd was also affected by phosphate, and the net effect of phosphate depended upon the surface charge of CeO2NPs.

Phytoremediation of Cd and Pb interactive polluted soils by switchgrass (Panicum virgatum L.)

Using phytoremediation as an efficient technique to remove heavy metals from contaminated soils is a current research hotspot. This study used an orthogonal matrix experimental design with three factors (Cd, Pb, and pH) and five levels (Cd at 9.45, 30, 60, 90, and 110.46 µg/g; Pb at 195.4, 400, 700, 1000, and 1204.6 µg/g; and pH at 3, 4.1, 5.8, 7.5, and 8.6) to investigate the phytoremediation potential of Panicum virgatum L. for soils polluted with cadmium (Cd) and lead (Pb). The results indicated that there was a significant decrease in belowground biomass in plants exposed to the stresses compared to the control. Superoxide dismutase (SOD) activity, peroxidase (POD) activity, and malondialdehyde (MDA) content were affected. Interaction of Cd with Pb in the soil had an antagonistic effect on the Cd bioaccumulation factor, whereas the interaction of pH with Cd or Pb had synergistic effects on the Cd bioaccumulation factor. When exposed to the three stressors, switchgrass plants could grow in soil that had a Cd concentration of a 46.68 µg/g, Pb concentration of 568.75 µg/g and pH of 5.34, which is a mildly acidic condition. Switchgrass, used as a phytoremediation plant, was more efficient in Cd-contaminated than in Pb-contaminated soil.

Irrigation Water Quality—A Contemporary Perspective

In the race to enhance agricultural productivity, irrigation will become more dependent on poorly characterized and virtually unmonitored sources of water. Increased use of irrigation water has led to impaired water and soil quality in many areas. Historically, soil salinization and reduced crop productivity have been the primary focus of irrigation water quality. Recently, there is increasing evidence for the occurrence of geogenic contaminants in water. The appearance of trace elements and an increase in the use of wastewater has highlighted the vulnerability and complexities of the composition of irrigation water and its role in ensuring proper crop growth, and long-term food quality. Analytical capabilities of measuring vanishingly small concentrations of biologically-active organic contaminants, including steroid hormones, plasticizers, pharmaceuticals, and personal care products, in a variety of irrigation water sources provide the means to evaluate uptake and occurrence in crops but do not resolve questions related to food safety or human health effects. Natural and synthetic nanoparticles are now known to occur in many water sources, potentially altering plant growth and food standard. The rapidly changing quality of irrigation water urgently needs closer attention to understand and predict long-term effects on soils and food crops in an increasingly fresh-water stressed world.

Salicylic Acid Signals Plant Defence against Cadmium Toxicity

Salicylic acid (SA), as an enigmatic signalling molecule in plants, has been intensively studied to elucidate its role in defence against biotic and abiotic stresses. This review focuses on recent research on the role of the SA signalling pathway in regulating cadmium (Cd) tolerance in plants under various SA exposure methods, including pre-soaking, hydroponic exposure, and spraying. Pretreatment with appropriate levels of SA showed a mitigating effect on Cd damage, whereas an excessive dose of exogenous SA aggravated the toxic effects of Cd. SA signalling mechanisms are mainly associated with modification of reactive oxygen species (ROS) levels in plant tissues. Then, ROS, as second messengers, regulate a series of physiological and genetic adaptive responses, including remodelling cell wall construction, balancing the uptake of Cd and other ions, refining the antioxidant defence system, and regulating photosynthesis, glutathione synthesis and senescence. These findings together elucidate the expanding role of SA in phytotoxicology.

Chelators induced uptake of cadmium and modulation of water relation, antioxidants, and photosynthetic traits of maize

The present study was aimed to reveal the effect of cadmium (Cd)-polluted soil on the activation of antioxidant enzymes, photosynthesis, pigments, water relation, and other biochemical traits and comparative effect of synthetic and organic chelators. A pot experiment was conducted using two maize varieties grown in Cd-contaminated (15 and 30 mg kg^-1) soil and chelators (1 mM EDTA, and 1 mM citric acid). Cd decreased biomass and photosynthetic traits while increased malondialdehyde (MDA) contents, total proteins, and antioxidant enzyme activities. Addition of EDTA enhanced Cd uptake, antioxidative enzyme, and total proteins; however, it reduced the water, osmotic, and turgor potential as compared to Cd alone. Addition of citric acid has lessened the antioxidant enzyme activities and MDA contents and enhanced the plant biomass as compared to Cd alone. Increases in antioxidants and MDA content were found to be positively related to the Cd contents in shoot and root. The application of citric acid significantly alleviated the Cd-induced toxic effects, showing remarkable improvement in biomass. These results indicated that EDTA was more effective for mobilizing Cd from soil to the root and shoot than citric acid; however, the physiological traits and plant biomass were more strongly inhibited by EDTA than by the Cd. Our study implies that citric acid ameliorated the negative effect of Cd on physiological traits and biomass, and hence could be used effectively for Cd phytoextraction.

Effect of cadmium on young plants of Virola surinamensis

The steady increase in cadmium (Cd) levels in the environment from anthropogenic actions has contributed to environmental degradation. Virola surinamensis is a forest species that has desirable characteristics such as deep and dense roots, relatively rapid growth and high biomass production to remedy contaminated environments by Cd. The aim of this study was to assess the physiological responses and the phytoextraction and tolerance capacity of young plants of V. surinamensis submitted to Cd concentrations. The experimental design was a completely randomized design with five Cd concentrations (0, 15, 30, 45 and 60 mg L^-1) for 60 days. Leaf water potential (Ψ_pd), stomatal conductance (gs) and transpiration (E) reduced in plants exposed to Cd. Lower values of maximum photochemical efficiency of photosystem II (Fv/Fm), electron transport rate (ETR) and photochemical quenching coefficient (qP) were accompanied by reduction of photosynthesis (A) with increasing concentrations of Cd, although the non-photochemical quenching coefficient (NPQ), and intercellular CO₂ concentration (Ci) showed increase. Instantaneous water-use efficiency (A/E), net photosynthesis to intercellular CO₂ concentration ratio (A/Ci) and total chlorophyll (Chl) reduced with increasing levels of Cd. Cadmium concentrations increased in different plant tissues (root > stem > leaf). The tolerance index (TI) indicated that V. surinamensis presented medium and high tolerance to Cd. The results of bioconcentration factor (BCF) and translocation factor (TF) showed low plant efficacy in Cd phytoextraction and suggest that V. surinamensis may be promising for phytostabilization of Cd.

Cd2+ influences metabolism and elemental distribution in roots of Acanthus ilicifolius L

Effect of cadmium (Cd) on the primary metabolic activities and elemental distribution in roots was explored in Acanthus ilicifolius L., a halophyte with phytostabilization potential. The rate of photosynthesis decreased in the CdCl₂ treated plants and this reduction was mainly attributed to the reduction of leaf area, photosynthetic pigments, impaired gaseous exchange caused by the stomatal closure and tissue water status. However, respiration rate was significantly higher in the CdCl₂ treated plants which aid the plant with additional energy required for the metabolic activities. Distribution of essential elements in the roots exhibited significant differences from that of control, which indicate the nutritional adaptation developed by A. ilicifolius under the influence of toxic metal ions. Thus, Cd toxicity is neutralized through the resource allocation from the growth process to processes that increase the fitness of the plant to encounter adverse environmental condition. In addition, the absorbed Cd is retained in the cortical cells of root thereby preventing the upward movement to shoot thereby making the plant a potential candidate for phytostabilization of Cd.

Comparative Transcriptomic Studies on a Cadmium Hyperaccumulator Viola baoshanensis and Its Non-Tolerant Counterpart V. inconspicua

Many Viola plants growing in mining areas exhibit high levels of cadmium (Cd) tolerance and accumulation, and thus are ideal organisms for comparative studies on molecular mechanisms of Cd hyperaccumulation. However, transcriptomic studies of hyperaccumulative plants in Violaceae are rare. Viola baoshanensis is an amazing Cd hyperaccumulator in metalliferous areas of China, whereas its relative V. inconspicua is a non-tolerant accumulator that resides at non-metalliferous sites. Here, comparative studies by transcriptome sequencing were performed to investigate the key pathways that are potentially responsible for the differential levels of Cd tolerance between these two Viola species. A cascade of genes involved in the ubiquitin proteosome system (UPS) pathway were observed to have constitutively higher transcription levels and more activation in response to Cd exposure in V. baoshanensis, implying that the enhanced degradation of misfolded proteins may lead to high resistance against Cd in this hyperaccumulator. Many genes related to sucrose metabolism, especially those involved in callose and trehalose biosynthesis, are among the most differentially expressed genes between the two Viola species, suggesting a crucial role of sucrose metabolism not only in cell wall modification through carbon supply but also in the antioxidant system as signaling molecules or antioxidants. A comparison among transcriptional patterns of some known transporters revealed that several tonoplast transporters are up-regulated in V. baoshanensis under Cd stress, suggesting more efficient compartmentalization of Cd in the vacuoles. Taken together, our findings provide valuable insight into Cd hypertolerance in V. baoshanensis, and the corresponding molecular mechanisms will be useful for future genetic engineering in phytoremediation.

Effect of EDTA and NTA on cadmium distribution and translocation in Pennisetum purpureum Schum cv. Mott

The primary objective of this research was to investigate the cadmium (Cd) distribution in Pennisetum purpurem (Napier grass) in the presence of 30 mg/L of Cd and different types and concentrations of chelating agents (ethylenediaminetetraacetic acid disodium dihydrate (EDTA), nitrilotriacetic acid (NTA), and EDTA-NTA mixtures). Plant samples were collected every 15 d during a 105-d experimental period. Accumulation of Cd in each part of the plant was determined using atomic absorption spectrometer (AAS), and the distribution of Cd was determined by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) and synchrotron radiation micro X-ray fluorescence (SR-micro-XRF). The highest concentrations of Cd accumulation of 889 ± 53 mg kg^-1 in the underground part (roots) and 265 ± 26 mg kg^-1 in the aboveground part (stems and leaves) in the presence of 1:1 M ratio of Cd:EDTA after 30 d of exposure were observed. Plants grown in the presence of either NTA or EDTA-NTA mixtures showed significant lower Cd accumulation levels. The LA-ICP-MS analysis showed that Cd was primarily accumulated in the aboveground part (stems and leaves), especially in the xylem and intercalary meristem. In addition, translocation factor was very low. Thus, P. purpurem could be considered as a candidate plant for cadmium phytostabilization.