Heavy Metals in Crop Plants: Transport and Redistribution Processes on the Whole Plant Level

The accumulation of cadmium and lead in wheat grains is primarily determined by the soil-reducible cadmium level during wheat tillering

The significant increase in cadmium (Cd) and lead (Pb) pollution in agricultural soil has greatly heightened environmental contamination issues and the risk of human diseases. However, the mechanisms underlying the transformation of Cd and Pb in soil as well as the influencing factors during their accumulation in crop grains remain unclear. Based on the analysis of the distribution trend of Cd and Pb in soil during the growth and development stages of wheat (tillering, filling, and maturity) in alkaline heavy metal-polluted farmland in northern China, this study investigated the response mechanism of soil heavy metal form transformation to soil physicochemical properties, and elucidated the main determining periods and influencing factors for Cd and Pb enrichment in wheat grains. The results showed that an increase in CEC and SOM levels, along with a decrease in pH level, contributed to enhancing the bioavailability of Cd in the soil. This effect was particularly evident during the tillering stage and grain filling stage of wheat. Nevertheless, the effects of soil physicochemical properties on bioavailable Pb was opposite to that on bioavailable Cd. The enrichment of Cd and Pb in grain was significantly influenced by soil pH (r = -0.786, p < 0.01), SOM (r = 0.807, p < 0.01), K (r = -0.730, p < 0.01), AK (r = 0.474, p = 0.019), and AP (r = -0.487, p = 0.016). The reducible form of Cd in soil during the wheat tillering stage was identified as the primary factor contributing to the accumulation of Cd and Pb in wheat grains, with a significant contribution rate of 84.5%. This study provides a greater scientific evidence for the management and risk control of heavy metal pollution in alkaline farmland.

Bismuth interaction with plants: Uptake and transport, toxic effects, tolerance mechanisms - A review

Bismuth (Bi) is a minor metal whose abundance on Earth is estimated at 0.025 ppm. Known since ancient times for its medical properties, its use in many industrial applications has increased significantly in recent years due to its physical and chemical properties. Considered less toxic than other metals, Bi has been defined as a "green metal" and has been suggested as a replacement for lead in many industrial processes. Although the occurrence of Bi in the environment is predicted to increase, there is still a lack of information on its interaction with biota. Even though it is absorbed by many organisms, Bi has not been directly implicated in the regulation of fundamental metabolic processes. This review summarises the fragmentary knowledge on the interaction between Bi and plants. Toxic effects at the growth, physiological and biochemical levels have been described in Bi-treated plants, with varying degrees and consequences for plant vitality, mostly depending on the chemical formulation of Bi, the concentration of Bi, the growth medium, the time of exposure, and the experimental conditions (laboratory or outdoor conditions). Bismuth has been shown to be readily absorbed and translocated in plants, interfering with plant growth and development, photosynthetic processes, nutrient uptake and accumulation, and metal (especially iron) homeostasis. Like other metals, Bi can induce an oxidative stress state in plant cells, and genotoxic effects have been reported in Bi-treated plants. Tolerance responses to the excess presence of Bi have been poorly described and are mostly referred to as the activation of antioxidant defences involving enzymatic and non-enzymatic molecules. The goal of this review is to offer an overview of the present knowledge on the interaction of Bi and plants, highlighting the gaps to be filled to better understand the role of Bi in affecting key physiological processes in plants. This will help to assess the potential harm of this metal in the environment, where its occurrence is predicted to increase due to the growing demand for medicinal and industrial applications.

Native desert plants have the potential for phytoremediation of phytotoxic metals in urban cities: implications for cities sustainability in arid environments

Arid regions can benefit from using native desert plants, which require minimal freshwater and can aid in remediating soil phytotoxic metals (PTMs) from traffic emissions. In this study, we assessed the ability of three native desert plants-Pennisetum divisum, Tetraena qatarensis, and Brassica tournefortii-to accumulate phytotoxic metals (PTMs) in their different plant organs, including leaves, stems, and roots/rhizomes. The PTMs were analyzed in soil and plant samples collected from Dubai, United Arab Emirates (UAE). The results indicated significantly higher levels of PTMs on the soil surface than the subsurface layer. Brassica exhibited the highest concentrations of Fe and Zn, measuring 566.7 and 262.8 mg kg-1, respectively, while Tetraena accumulated the highest concentration of Sr (1676.9 mg kg-1) in their stems. In contrast, Pennisetum recorded the lowest concentration of Sr (21.0 mg kg-1), while Tetraena exhibited the lowest concentrations of Fe and Zn (22.5 and 30.1 mg kg-1) in their leaves. The roots of Pennisetum, Brassica, and Tetraena demonstrated the potential to accumulate Zn from the soil, with concentration factors (CF) of 1.75, 1.09, and 1.09, respectively. Moreover, Brassica exhibited the highest CF for Sr, measuring 2.34. Pennisetum, however, could not translocate PTMs from its rhizomes to other plant organs, as indicated by a translocation factor (TF) of 1. In contrast, Brassica effectively translocated the studied PTMs from its roots to the stem and leaves (except for Sr in the leaves). Furthermore, Pennisetum exclusively absorbed Zn from the soil into its leaves and stems, with an enrichment factor (EF) greater than 1. Brassica showed the ability to uptake the studied PTMs in its stem and leaves (except for Fe), while Tetraena primarily absorbed Sr and Zn into its stems. Based on the CF and TF results, Pennisetum appears to be a suitable species for phytostabilization of both Fe and Zn, while Brassica is well-suited for Sr and Zn polluted soils. Tetraena shows potential for Zn phytoremediation. These findings suggest that these plants are suitable for PTMs phytoextraction. Furthermore, based on the EF results, these plants can efficiently sequester PTMs.

Evaluating the efficacy of vermicomposted products in rain-fed wetland rice and predicting potential hazards from metal-contaminated tannery sludge using novel machine learning tactic

The study assessed the ecotoxicity and bioavailability of potential metals (PMs) from tannery waste sludge, alongside addressing the environmental concerns of overuse of chemical fertilizers, by comparing the impacts of organic vermicomposted tannery waste, chemical fertilizers, and sole application of tannery waste on soil and rice (Oryza sativa L.) plants. The results revealed that T3, which received high-quality vermicomposted tannery waste as an amendment, exhibited superior enzymatic characteristics compared to tannery sludge amended (TWS) treatments (T8, T9). After harvesting, vermicomposted tannery waste treatment (T3) showed a more significant decrease in PMs bioavailability. Accumulation of PMs in rice was minimal across all treatments except T8 and T9, where toxic tannery waste was present, resulting in a high-risk classification (class 5 < 0.01) according to the SAMOE risk assessment. Results from Fuzzy-TOPSIS, ANN, and Sobol sensitivity analyses (SSA) further indicated that elevated concentrations of PMs (Ni, Pb, Cr, Cu) adversely impacted soil-plant health synergy, with T3 showing a minimal risk in comparison to T8 and T9. According to SSA, microbial biomass carbon and acid phosphatase activity were the most sensitive factors affected by PMs concentrations in TWS. The results from the ANN assay revealed that the primary contributing factor of toxicity on the TWS was the exchangeable fraction of Cr. Correlation statistics underscored the significant detrimental effect of PMs' bioavailability on microbial and enzymatic parameters. Overall, the findings suggest that vermicomposting of tannery sludge waste shows potential as a viable organic amendment option in the near future.

Effect of MnO2 Nanoparticles Stabilized with Cocamidopropyl Betaine on Germination and Development of Pea (Pisum sativum L.) Seedlings

This study aimed to synthesize, characterize, and evaluate the effect of cocamidopropyl betaine-stabilized MnO2 nanoparticles (NPs) on the germination and development of pea seedlings. The synthesized NPs manifested as aggregates ranging from 50-600 nm, comprising spherical particles sized between 19 to 50 nm. These particles exhibited partial crystallization, indicated by peaks at 2θ = 25.37, 37.62, 41.18, 49.41, 61.45, and 65.79°, characteristic of MnO2 with a tetragonal crystal lattice with a I4/m spatial group. Quantum chemical modelling showed that the stabilization process of MnO2 NPs with cocamidopropyl betaine is energetically advantageous (∆E > 1299.000 kcal/mol) and chemically stable, as confirmed by the positive chemical hardness values (0.023 ≤ η ≤ 0.053 eV). It was revealed that the interaction between the MnO2 molecule and cocamidopropyl betaine, facilitated by a secondary amino group (NH), is the most probable scenario. This ascertain is supported by the values of the difference in total energy (∆E = 1299.519 kcal/mol) and chemical hardness (η = 0.053 eV). These findings were further confirmed using FTIR spectroscopy. The effect of MnO2 NPs at various concentrations on the germination of pea seeds was found to be nonlinear and ambiguous. The investigation revealed that MnO2 NPs at a concentration of 0.1 mg/L resulted in the highest germination energy (91.25%), germinability (95.60%), and lengths of roots and seedlings among all experimental samples. However, an increase in the concentration of preparation led to a slight growth suppression (1-10 mg/L) and the pronounced inhibition of seedling and root development (100 mg/L). The analysis of antioxidant indicators and phytochemicals in pea seedlings indicated that only 100 mg/L MnO2 NPs have a negative effect on the content of soluble sugars, chlorophyll a/b, carotenoids, and phenols. Conversely, lower concentrations showed a stimulating effect on photosynthesis indicators. Nevertheless, MnO2 NPs at all concentrations generally decreased the antioxidant potential of pea seedlings, except for the ABTS parameter. Pea seedlings showed a notable capacity to absorb Mn, reaching levels of 586.5 μg/L at 10 mg/L and 892.6 μg/L at 100 mg/L MnO2 NPs, surpassing the toxic level for peas according to scientific literature. However, the most important result was the observed growth-stimulating activity at 0.1 mg/L MnO2 NPs stabilized with cocamidopropyl betaine, suggesting a promising avenue for further research.

The Influence of Copper and Zinc on Photosynthesis and Phenolic Levels in Basil (Ocimum basilicum L.), Borage (Borago officinalis L.), Common Nettle (Urtica dioica L.) and Peppermint (Mentha piperita L.)

This work is aimed at relationships which govern zinc and copper uptake by four popular medicinal herbs: basil (Ocimum basilicum L.), borage (Borago officinalis L.), common nettle (Urtica dioica L.) and peppermint (Mentha piperita L.). They are often grown in soils with significant copper or zinc levels. Herbs were cultivated by a pot method in controlled conditions. Manganese, iron, copper and zinc concentrations were determined by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry. The efficiency of photosynthesis was estimated by measuring the chlorophyll content, water use efficiency, net photosynthesis, intercellular CO2, stomatal conductance, and transpiration rate. Phenolic compounds were determined by the Folin-Ciocalteu method. Analysis of variance showed that herbs grown in soil treated with copper exhibited a lower iron content in roots, while manganese behaved in the opposite way. The only exception was borage, where a decrease in the manganese content in roots was observed. Both copper and zinc supplementations increased the total content of phenolics, while the highest increases were observed for common nettle and basil. Peppermint and borage responded less to supplementation. In the majority of samples, zinc and copper did not significantly affect the photosynthesis. Herbal extracts from common nettle and basil had unique antioxidant properties and may be good free radical scavengers.

Integrated morphological, physiological and transcriptomic analyses reveal response mechanisms of rice under different cadmium exposure routes

Rice (Oryza sativa) is one of the major cereal crops and takes up cadmium (Cd) more readily than other crops. Understanding the mechanism of Cd uptake and defense in rice can help us avoid Cd in the food chain. However, studies comparing Cd uptake, toxicity, and detoxification mechanisms of leaf and root Cd exposure at the morphological, physiological, and transcriptional levels are still lacking. Therefore, experiments were conducted in this study and found that root Cd exposure resulted in more severe oxidative and photosynthetic damage, lower plant biomass, higher Cd accumulation, and transcriptional changes in rice than leaf Cd exposure. The activation of phenylpropanoids biosynthesis in both root and leaf tissues under different Cd exposure routes suggests that increased lignin is the response mechanism of rice under Cd stress. Moreover, the roots of rice are more sensitive to Cd stress and their adaptation responses are more pronounced than those of leaves. Quantitative PCR revealed that OsPOX, OsCAD, OsPAL and OsCCR play important roles in the response to Cd stress, which further emphasize the importance of lignin. Therefore, this study provides theoretical evidence for future chemical and genetic regulation of lignin biosynthesis in crop plants to reduce Cd accumulation.

Impact of lead and zinc heavy metal pollution on the growth and phytoremediation potential of Sulla carnosa in Sebkha el Kalbia, Tunisia

Heavy metal pollution from human and natural activities poses significant environmental and health concerns for wildlife and humans, with lead and zinc being particularly threatening. This study focuses on Sebkha el Kalbia in Tunisia, highlighting the challenges faced by local communities in addressing heavy metal pollution. The area is prone to contamination through rivers and streams that transport pollutants from industrial zones and rural areas into the salt pan. The recent establishment of an industrial zone has worsened pollution levels, calling for strict regulatory measures and clean technologies to limit heavy metal pollution and protect human health and the environment. The study assesses the impact of lead and zinc pollution on the growth of Sulla carnosa and its potential for phytoremediation. Soil and plant samples from contaminated areas were analyzed, revealing high levels of heavy metal contamination. The growth parameters of Sulla carnosa, such as plant height, weight, and enzymatic activity, were examined, showing a significant reduction in plant growth when exposed to high metal concentrations. Specifically, in the presence of 100 ppm of lead (Pb), net photosynthetic assimilation (An) decreased by 52%, while the amount of Pb increased by 78%. At 800 ppm of Pb, An decreased by 87%, and the amount of Pb increased by over 800%. Furthermore, the relationship between net photosynthetic assimilation and lead (Pb) content remained significant but negative. At high doses (800 ppm), the biomass produced decreases by 64%, while the amount of Zn increases 2.7 times. These results suggest that at low doses, zinc is not toxic. These findings highlight Sulla carnosa as a potential candidate for phytoremediation with preferential metal accumulation in the roots and improved enzymatic activity, underscoring the urgency of addressing heavy metal pollution in Sebkha el Kalbia.

Efficiency of sodium phytate in the remediation of As, Mn, and Cu contamination in acid mine drainage using water hyacinth

The accumulation and uptake efficiency of heavy metals, including As, Mn, and Cu, in water hyacinth (Eichhornia crassipes (Mart.) Solms) grown in synthetic acidic wastewater supplemented with sodium phytate (SP) was examined. Three treatments were studied using synthetic acidic wastewater containing 0.25, 5.0, and 1.0 mg/L of As, Mn, and Cu, respectively, (SM + heavy metals) and having pH in the range of 4-6, which comprised of (1) control treatments using SM + heavy metals at pH 4, 5, 6 without SP, and treatments using SM + heavy metals at pH 4, 5, 6 with SP: Cu (2) in a 1:3 M ratio and (3) a 1:6 M ratio. The translocation factor (TF < 1) indicated that plants had a lower capacity to transport heavy metals from the roots to the stems. The shoots of water hyacinth exhibited the highest capacity to absorb and store As in the pH 4-treatment with SP (SP:Cu1:3 mol), whereas the roots showed the greatest capacity at pH 4 without SP. The roots and shoots of the water hyacinth showed the greatest capacity to take up and store Mn in the pH 5-treatment with a 1:3 M ratio of SP:Cu. The roots showed the greatest capacity to take up and store Cu in the pH 6-treatment, and the shoots showed the highest capability in the pH 5-treatment with 1:3 M ratio of SP:Cu. Moreover, analysis of the chemical forms revealed that As accumulated in the arsenate form, whereas Mn accumulated in the divalent form.

Safe utilization evaluation of two typical traditional Chinese medicinal materials in Cd-contaminated soil based on the analysis of Cd transfer and AHP model

Due to the increasing scarcity of wild resources, most traditional Chinese medicinal materials (TCMMs) in the market are produced via artificial cultivation. The widespread pollution of cadmium (Cd) in soil limits the safe cultivation and use of TCMMs. This study investigated Cd accumulation, distribution, and the medicinal component content under simulated field conditions to clarify the differences in the Cd absorption, transfer and detoxification mechanisms of Polygonatum cyrtonema Hua and Bletilla striata, and provide the preliminary safe utilization conditions of TCMMs based on the analytic hierarchy process (AHP). The results showed that the Cd content of P. cyrtonema Hua was lower than the safety threshold under a high soil Cd concentration of 0.91 mg/kg (Cd-L), while B. striata was safe only at a low Cd concentration of 0.25 mg/kg (CK). Cd at 0.91 mg/kg induced hormesis affecting the net increase in biomass and medicinal component content for both TCMMs, while P. cyrtonema Hua showed better potential for safe utilization. Additionally, P. cyrtonema Hua had stronger resistance to Cd stress, exhibiting superior characteristics for synergistic absorption of Cd with mineral elements, transfer to nonmedical part and safer fixation forms in subcellular components. In contrast, B. striata showed insufficient Cd tolerance, and Cd was easily accumulated in organelles to inhibit plant growth. Our findings may attract more attention to the safe cultivation of TCMMs and provide insight into guidance for the safe utilization of slightly Cd-contaminated soil.

Enzymes Involved in Antioxidant and Detoxification Processes Present Changes in the Expression Levels of Their Coding Genes under the Stress Caused by the Presence of Antimony in Tomato

Currently, there is an increasing presence of heavy metals and metalloids in soils and water due to anthropogenic activities. However, the biggest problem caused by this increase is the difficulty in recycling these elements and their high permanence in soils. There are plants with great capacity to assimilate these elements or make them less accessible to other organisms. We analyzed the behavior of Solanum lycopersicum L., a crop with great agronomic interest, under the stress caused by antimony (Sb). We evaluated the antioxidant response throughout different exposure times to the metalloid. Our results showed that the enzymes involved in the AsA-GSH cycle show changes in their expression level under the stress caused by Sb but could not find a relationship between the NITROSOGLUTATHIONE REDUCTASE (GSNOR) expression data and nitric oxide (NO) content in tomato roots exposed to Sb. We hypothesize that a better understanding of how these enzymes work could be key to develop more tolerant varieties to this kind of abiotic stress and could explain a greater or lesser phytoremediation capacity. Moreover, we deepened our knowledge about Glutathione S-transferase (GST) and Glutathione Reductase (GR) due to their involvement in the elimination of the xenobiotic component.

Targeted Delivery of Sucrose-Coated Nanocarriers with Chemical Cargoes to the Plant Vasculature Enhances Long-Distance Translocation

Current practices for delivering agrochemicals are inefficient, with only a fraction reaching the intended targets in plants. The surfaces of nanocarriers are functionalized with sucrose, enabling rapid and efficient foliar delivery into the plant phloem, a vascular tissue that transports sugars, signaling molecules, and agrochemicals through the whole plant. The chemical affinity of sucrose molecules to sugar membrane transporters on the phloem cells enhances the uptake of sucrose-coated quantum dots (sucQD) and biocompatible carbon dots with β-cyclodextrin molecular baskets (suc-β-CD) that can carry a wide range of agrochemicals. The QD and CD fluorescence emission properties allowed detection and monitoring of rapid translocation (<40 min) in the vasculature of wheat leaves by confocal and epifluorescence microscopy. The suc-β-CDs more than doubled the delivery of chemical cargoes into the leaf vascular tissue. Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the fraction of sucQDs loaded into the phloem and transported to roots is over 6.8 times higher than unmodified QDs. The sucrose coating of nanoparticles approach enables unprecedented targeted delivery to roots with ≈70% of phloem-loaded nanoparticles delivered to roots. The use of plant biorecognition molecules mediated delivery provides an efficient approach for guiding nanocarriers containing agrochemicals to the plant vasculature and whole plants.

Cadmium toxicity: its' uptake and retaliation by plant defence system and ja signaling

Cadmium (Cd+2) renders multifarious environmental stresses and highly toxic to nearly all living organisms including plants. Cd causes toxicity by unnecessary augmentation of ROS that targets essential molecules and fundamental processes in plants. In response, plants outfitted a repertory of mechanisms to offset Cd toxicity. The main elements of these are Cd chelation, sequestration into vacuoles, and adjustment of Cd uptake by transporters and escalation of antioxidative mechanism. Signal molecules like phytohormones and reactive oxygen species (ROS) activate the MAPK cascade, the activation of the antioxidant system andsynergistic crosstalk between different signal molecules in order to regulate plant responses to Cd toxicity. Transcription factors like WRKY, MYB, bHLH, bZIP, ERF, NAC etc., located downstream of MAPK, and are key factors in regulating Cd toxicity responses in plants. Apart from this, MAPK and Ca2+signaling also have a salient involvement in rectifying Cd stress in plants. This review highlighted the mechanism of Cd uptake, translocation, detoxification and the key role of defense system, MAPKs, Ca2+ signals and jasmonic acid in retaliating Cd toxicity via synchronous management of various other regulators and signaling components involved under stress condition.

Foliar zinc spraying improves assimilative capacity of sugar beet leaves by promoting magnesium and calcium uptake and enhancing photochemical performance

Sugar beet, a zinc-loving crop, is increasingly limited by zinc deficiency worldwide. Foliar zinc application is an effective and convenient way to supplement zinc fertilizer. However, the regulatory mechanism of foliar zinc spraying on sugar beet leaf photosynthetic characteristics remains unclear. Therefore, we investigated the effects of foliar ZnSO4·7H2O application (0, 0.1%, 0.2%, and 0.4%) on the photosynthetic performance of sugar beet leaves under controlled hydroponic conditions. The results indicated that a foliar spray of 0.2% Zn fertilizer was optimal for promoting sugar beet leaf growth. This concentration significantly reduced the leaf shape index of sugar beet, notably increasing leaf area, leaf mass ratio, and specific leaf weight. Foliar spraying of Zn (0.2%) substantially elevated the Zn content in sugar beet leaves, along with calcium (Ca) and magnesium (Mg) contents. Consequently, this led to an increase in the potential photochemical activity of PSII (Fv/Fo) (by 6.74%), net photosynthetic rate (Pn) (11.39%), apparent electron transport rate (ETR) (11.43%), actual photochemical efficiency of PSⅡ (Y (Ⅱ)) (11.46%), photochemical quenching coefficient (qP) (15.49%), and total chlorophyll content (25.17%). Ultimately, this increased sugar beet leaf dry matter weight (11.30%). In the cultivation and management of sugar beet, the application of 0.2% Zn fertilizer (2.88 mg plant-1) exhibited the potential to enhance Zn and Mg contents in sugar beet, improve photochemical properties, stimulate leaf growth, and boost light assimilation capacity. Our result suggested the foliar application of Zn might be a useful strategy for sugar beet crop management.

Effect of sludge amelioration on yield, accumulation and translocation of heavy metals in soybean grown in acid and alkaline soils

A greenhouse pot experiment was conducted with seven different levels of sludge (0, 5, 10, 20, 40, 80, 160 g kg-1) to assess the potential impact of sludge application on soybean (Glycine max (L.) Merr.) productivity, metal accumulation and translocation, and physico-chemical changes in acid and alkaline soils. The outcomes revealed that the application of sludge @ 5.0 to 160 g kg-1 resulted in a significant (p < 0.05) increase in seed and straw yield in both acid and alkaline soils compared to control. All the assessed heavy metals in soybean were within permissible ranges and did not exceed the phytotoxic limit, except for Fe, Zn, and Cu in the roots from the application of sewage sludge. The values of bioaccumulation factor (BFroot/soil) and translocation factor i.e., TFstraw/root and TFseed/straw were < 1.0 for Ni, Pb and Cr. Overall, for all the sludge application doses the soil pH was observed to increase in the acid soil and decline in alkaline soil when compared to the control. All the investigated heavy metals (Fe, Mn, Zn, Cu, Ni, Cd, Pb, and Cr) in the different plant tissues (root, straw and seed) of soybean were correlated with the soil variables. The study finds that sludge can be a potential organic fertilizer and function as an eco-friendly technique for the recycling of nutrients in the soil while keeping a check on the heavy metals' availability to plants.

Relationship between different physiological processes of Tomato seedlings exposed to acid mine water Uncovered using correlation analysis

This study was conducted to assess the correlation between growth response, phytoaccumulation factor of different tissues, and elemental composition in tomato seedlings exposed to acid mine water (AMW). In pairwise correlation determinations values of plant height, stem diameter, seed germination indices (radicle length, final germination percentage (FGP), emergency rate index (ERI), vigour index (VI), germination percentage (G%) and germination rate index (GRI)) and the elemental compositions (Cd, Cr, Cu, Ni and Zn) in the different plant tissues, root (root accumulation factor = RAF), stem (stem translocation factor = STF) and leaves (leaf translocation factor = LTF) were selected for the relationship determinations. Pearson correlation coefficients were calculated and revealed the relationships between the paired parameters. The study concluded that the strongly correlated physiological parameters were jointly co-ordinated in tomato seedlings exposed to AMW.

Some Physiological Effects of Nanofertilizers on Wheat-Aphid Interactions

The increasing use of nanofertilizers in modern agriculture and their impact on crop yield and pest management require further research. In this study, the effects of nano-Fe, -Zn, and -Cu (which are synthesized based on nanochelating technology), and urea (N) fertilizers on the antioxidant activities of wheat plants (cv. Chamran), and the wheat green aphid Schizaphis graminum (Rondani) are investigated. The authors observed the highest levels of phenolics in non-infested nano-Zn-treated plants (26% higher compared with control). The highest H₂O₂ levels are in the infested and non-infested nano-Zn-treated and infested nano-Fe-treated plants (in infested nano-Zn and nano-Fe treated plants, 18% and non-infested nano-Zn-treated plants, 28% higher compared with control). The highest peroxidase (POX) activity is observed in the infested and non-infested N-treated and non-infested water-treated plants (almost 14%, 37%, and 46% higher than control, respectively). The lowest activity is in the infested plants' nano-Zn and -Fe treatments (almost 7 and 5 folds lower compared to the control, respectively). The highest and lowest catalase (CAT) activity are in the infested N-treated plants (almost 42% higher than control) and water-treated plants, respectively. The infested nano-Zn, -Fe, -Cu and Hoagland-treated plants showed the highest superoxide dismutase (SOD) activity. Regarding the antioxidant enzyme activities of S. graminum, the highest POX activity is in the nano-Cu treatment (more than two folds higher compared with control); the highest CAT and SOD activities are in the nano-Cu and -Zn treatments. It can be concluded that the application of nanofertilizers caused increasing effects on the wheat plant's antioxidant system and its resistance to S. graminum.

Foliar cadmium uptake, transfer, and redistribution in Chili: A comparison of foliar and root uptake, metabolomic, and contribution

Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdS_N), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

Uptake of heavy metals by crops near a mining field: Pathways from roots and leaves

Metal uptake and distribution in crops have been demonstrated to be highly variable and depending on the metal of interest and the crop type. However, no consensus is reached regarding the primary factor controlling metal uptake in crops. This study thus comparably investigated Hg, As, Zn, Pb, Cd and Cu uptake and distribution in three crops grown in a watershed near a copper mining field located in Yunnan, Southwestern China. The bioconcentration factor (BCF) and translocation factor (TF) were statistically compared for the same metal across different crops. Leafy crops had a stronger propensity to accumulate Hg, As and Zn than fruit crops. The ability of grain crops to accumulate Cd and Cu was much lower than leafy and fruit crops. The three crops all tended not to accumulate Pb in their edible tissues. The DTPA extracted metal concentrations were not statistically correlated with the metal concentrations in crop edible tissues. It is thus not practical to predict metal uptake of Hg, As, Pb and Zn through their available concentrations in soils. The contents of nitrogen and phosphorus, and competing metal ions present in paddy soil decreased the accumulation of Cu and Cd in rice grains. By means of hierarchical cluster analysis, the high accumulation of Zn in the edible tissues of fruit and grain crops was mainly due to dust inputs via phloem transport from leaves. This is why BCF(Zn) was the highest among the six metals for these two crops. For leafy crops, the accumulation of Hg, Cd and Zn in leaves was mainly through soil inputs by roots. Our findings serve as a scientific basis for the selection of crops in areas with high background of heavy metals.

An eco-sustainable approach towards heavy metals remediation by mangroves from the coastal environment: A critical review

Mangroves provide various ecosystem services, carbon sequestration, biodiversity depository, and livelihoods. They are most abundant in marine and coastal ecosystems and are threatened by toxic contaminants like heavy metals released from various anthropogenic activities. However, they have significant potential to survive in salt-driven environments and accumulate various pollutants. The adverse effects of heavy metals have been extensively studied and recognized as toxic to mangrove species. This study sheds light on the dynamics of heavy metal levels, their absorption, accumulation and transport in the soil environment in a mangrove ecosystem. The article also focuses on the potential of mangrove species to remove heavy metals from marine and coastal environments. This review concludes that mangroves are potential candidates to clean up contaminated water, soil, and sediments through their phytoremediation ability. The accumulation of toxic heavy metals by mangroves is mainly through roots with limited upward translocation. Therefore, promoting the maintenance of biodiversity and stability in the coastal environment is recommended as an environmentally friendly and potentially cost-effective approach.

Contamination, ecological, and health risk assessment of heavy metals and organophosphorus pesticides in single, double, and ratoon cropping of rice: a case study in Mazandaran, North of Iran

This study investigated the contamination and health risk assessment of heavy metals and organophosphorus pesticides in single, double, and ratoon cropping of rice in Mazandaran province, north of Iran. A total of 17 sampling locations in rice farms were selected and soil and rice samples were collected from farms in 5 counties of Mazandaran. Soil and rice samples were then transferred to the lab for further analysis. The concentration of pesticides and heavy metals was then analyzed using gas chromatography-mass spectrometry (GC-MS) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Mercury was analyzed using a Leco mercury analyzer. Target hazard quotient (THQ), total target hazard quotient (TTHQ), carcinogenic risk (CR), and total carcinogenic risk (TCR) in children and adults were used. Potential ecological risk also was used to test the possible hazards of heavy metals to the environment. Heavy metals concentration in rice and soil samples in different farming steps revealed different levels. THQ showed no considerable risk in consuming contaminated rice to adults and children considered, while TTHQ revealed potential non-carcinogenic risks. Ni had the most carcinogenic risks to target human groups, and TCR showed carcinogenicity for carcinogenic heavy metals in all stations. Findings showed no ecological risks of metals to the environment. In conclusion, rice farmers in Mazandaran use the lands multiple times during the year to increase the performance, function, quality, and quantity of rice, but the possible toxic effects of heavy metals and pesticides on consumers and the environment should not be overlooked.

Cadmium toxicity in medicinal plants: An overview of the tolerance strategies, biotechnological and omics approaches to alleviate metal stress

Medicinal plants, an important source of herbal medicine, are gaining more demand with the growing human needs in recent times. However, these medicinal plants have been recognized as one of the possible sources of heavy metal toxicity in humans as these medicinal plants are exposed to cadmium-rich soil and water because of extensive industrial and agricultural operations. Cadmium (Cd) is an extremely hazardous metal that has a deleterious impact on plant development and productivity. These plants uptake Cd by symplastic, apoplastic, or via specialized transporters such as HMA, MTPs, NRAMP, ZIP, and ZRT-IRT-like proteins. Cd exerts its effect by producing reactive oxygen species (ROS) and interfere with a range of metabolic and physiological pathways. Studies have shown that it has detrimental effects on various plant growth stages like germination, vegetative and reproductive stages by analyzing the anatomical, morphological and biochemical changes (changes in photosynthetic machinery and membrane permeability). Also, plants respond to Cd toxicity by using various enzymatic and non-enzymatic antioxidant systems. Furthermore, the ROS generated due to the heavy metal stress alters the genes that are actively involved in signal transduction. Thus, the biosynthetic pathway of the important secondary metabolite is altered thereby affecting the synthesis of secondary metabolites either by enhancing or suppressing the metabolite production. The present review discusses the abundance of Cd and its incorporation, accumulation and translocation by plants, phytotoxic implications, and morphological, physiological, biochemical and molecular responses of medicinal plants to Cd toxicity. It explains the Cd detoxification mechanisms exhibited by the medicinal plants and further discusses the omics and biotechnological strategies such as genetic engineering and gene editing CRISPR- Cas 9 approach to ameliorate the Cd stress.

Phytoremediation with kenaf (Hibiscus cannabinus L.) for cadmium-contaminated paddy soil in southern China: translocation, uptake, and assessment of cultivars

Kenaf (Hibiscus cannabinus L.) is suitable for growing in heavy metal-polluted soil for non-food purposes and can be used as a potential crop to remediate heavy metal-contaminated soil. The main objective of this study was to investigate kenaf phytoextraction of cadmium (Cd), including uptake, translocation, and accumulation differences in tissues among kenaf cultivars. A field experiment was conducted in a Cd contaminated paddy field in southern China area with 13 kenaf cultivars in 2015 and 2016. Agronomic performance, Cd concentrations in plant tissues (root, xylem, and phloem), and biomass of different tissues of each cultivar were measured and evaluated. Significant differences in Cd concentrations and accumulation among tissues and cultivars were observed. The phloem had the highest Cd accumulation and transfer capability compared with the roots and xylem. Approximately 35 ~ 65 g of Cd could be taken up by the aerial parts of different kenaf cultivars within every hectare of soil. The percentage of Cd uptake by the phloem ranged from 47 to 61% and by the xylem ranged from 38 to 53%. By evaluating the agronomic traits and Cd bioaccumulation capacity, Fuhong 952, Fuhong 992, and Fuhong R1 were regarded as Cd accumulators for the phytoremediation of Cd-contaminated soil. Our study clearly demonstrated that a significant level of Cd in the soil was taken up through the phytoremediation with kenaf. In addition, harmless utilization of kenaf planting in Cd-contaminated paddy soil was discussed.

The Role of Membrane Transporters in the Biofortification of Zinc and Iron in Plants

Over three billion people suffer from various health issues due to the low supply of zinc (Zn) and iron (Fe) in their food. Low supply of micronutrients is the main cause of malnutrition and biofortification could help to solve this issue. Understanding the molecular mechanisms of biofortification is challenging. The membrane transporters are involved in the uptake, transport, storage, and redistribution of Zn and Fe in plants. These transporters are also involved in biofortification and help to load the Zn and Fe into the endosperm of the seeds. Very little knowledge is available on the role and functions of membrane transporters involved in seed biofortification. Understanding the mechanism and role of membrane transporters could be helpful to improve biofortification. In this review, we provide the details on membrane transporters involved in the uptake, transport, storage, and redistribution of Zn and Fe. We also discuss available information on transporters involved in seed biofortification. This review will help plant breeders and molecular biologists understand the importance and implications of membrane transporters for seed biofortification.

Effect of Heavy Metal Stress on Phenolic Compounds Accumulation in Winter Wheat Plants

Heavy metal stress can lead to many adverse effects that inhibit cellular processes at various levels of metabolism, causing a decrease in plant productivity. In response to environmental stressors, phenolic compounds fulfill significant molecular and biochemical functions in plants. Increasing the biosynthesis of phenolic compounds in plants subjected to heavy metal stress helps protect plants from oxidative stress. A pot experiment was carried out to determine the effect of the accumulation of copper (Cu) and lead (Pb) salts at concentrations of 200, 500, and 1000 ppm on seed germination, the activity of enzymes in the phenylalanine ammonia-lyase pathway (PAL) and tyrosine ammonia-lyase (TAL), along with the total phenol and flavonoid contents in seedlings of hybrid Triticum aestivum L. (winter wheat) cultivars. The accumulation of heavy metals, especially Cu, had a negative impact on the seed germination process. The cultivar "Hyacinth" reacted most strongly to heavy metal stress, which was confirmed by obtaining the lowest values of the germination parameters. Heavy metal stress caused an increase in the activity of PAL and TAL enzymes and an increase in the accumulation of phenolic compounds. Under the influence of Cu, the highest activity was shown in cv. "Hyvento" (especially at 200 ppm) and, due to the accumulation of Pb, in cv. "Hyacinth" (1000 ppm) and cv. "Hyking" (200 ppm). The cultivar "Hyking" had the highest content of phenolic compounds, which did not increase with the application of higher concentrations of metals. In other cultivars, the highest content of total phenols and flavonoids was usually observed at the lowest concentration (200 ppm) of the tested heavy metals, Cu and Pb.

Gibberellic acid improves growth and reduces heavy metal accumulation: A case study in tomato (Solanum lycopersicum L.) seedlings exposed to acid mine water

This study investigated the effect of gibberellic acid (GA₃) on the growth of tomato seedlings and heavy metal accumulation within seedlings tissue irrigated with acid mine water (AMW). Three experimental treatments were administered using a completely randomized design with five replicates. The experimental treatments included were gibberellic acid + acid mine water (GA₃ + AMW), acid mine water (AMW), and tap water. Seedlings were irrigated directly in pots with 400 mL of 100% AMW at two-day intervals 21 days after planting. Drenching of the seedlings with GA₃ was done every 24 h for eight consecutive days from 28 days after planting. Results on the physicochemical analysis showed high concentrations of heavy metals (HMs) in AMW compared to tap water and the experimental treatment significantly affected the measured plant growth parameters. Tomato plants irrigated with AMW alone were shorter (4.00 cm) than plants irrigated with tap water (14.00 cm), while plants treated with AMW and GA₃ were much taller (16.50 cm) than the latter (control). Moreover, HM accumulation differed among the three treatments. Seedlings that received AMW with no GA₃ accumulated more HMs (Cd, Cr, Cu, Ni, and Zn) in their roots, stems, and leaves while plants treated with GA₃ had a decrease in the accumulation and distribution of HMs in the different plant tissues (roots, stems, and leaves) relative to AMW alone and the plants irrigated with tap water alone. The study revealed that GA₃ boosted the growth of tomato seedlings irrigated with AMW and also altered HM accumulation with the tissues of the seedlings.

Effects of Heavy Metal Stress on Physiology, Hydraulics, and Anatomy of Three Desert Plants in the Jinchang Mining Area, China

The physiological mechanisms and phytoremediation effects of three kinds of native quinoa in a desert mining area were studied. We used two different types of local soils (native soil and tailing soil) to analyze the changes in the heavy metal content, leaf physiology, photosynthetic parameters, stem hydraulics, and anatomical characteristics of potted quinoa. The results show that the chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate of Kochia scoparia were decreased, but intercellular CO₂ concentration (Ci) was increased under heavy metal stress, and the net photosynthetic rate (Pn) was decreased due to non-stomatal limitation. The gas exchange of Chenopodium glaucum and Atriplex centralasiatica showed a decrease in Pn, stomatal conductance (Gs), and transpiration rate (E) due to stomatal limitation. The three species showed a similar change in heavy metal content; they all showed elevated hydraulic parameters, decreased vessel density, and significantly thickened vessel walls under heavy metal stress. Physiological indicators such as proline content and activity of superoxide dismutase (SOD) and peroxidase (POD) increased, but the content of malondialdehyde (MDA) and glutathione (GSH), as well as catalase (CAT) activity, decreased in these three plants. Therefore, it can be concluded that these three species of quinoa, possibly the most dominant 30 desert plants in the region, showed a good adaptability and accumulation capacity under the pressure of heavy metal stress, and these plants can be good candidates for tailings remediation in the Jinchang desert mining area.

Suppression of Cucumber Green Mottle Mosaic Virus Infection by Boron Application: From the Perspective of Nutrient Elements and Carbohydrates

Cucumber green mottle mosaic virus (CGMMV) infection causes "blood flesh" symptoms in watermelon fruits, which severely reduces yield and edibleness. However, the growth of watermelon fruits is strongly associated with boron (B), a trace element for improving fruit quality. In this study, B-gradient hydroponic experiments (B concentration: 0, 2.86, and 5.72 mg·L^-1 H₃BO₃) and foliar-spray experiments (B concentration: 30 and 300 mg·L^-1 H₃BO₃) were performed. We found that the B-supplement could inhibit CGMMV infection and especially relieve "blood flesh" symptoms in watermelon fruits. The nutrient element, soluble sugar, and cell wall polysaccharide contents and their metabolism- and transport-related gene expressions were determined in leaves and fruits of the watermelons in B-gradient hydroponic and foliar-spray experiments. We found that the accumulation and metabolism of nutrients and carbohydrates in cells were disrupted by CGMMV infection; however, the B-supplement could restore and maintain their homeostasis. Additionally, we uncovered that NIP5;1 and SWEET4, induced by B-application with CGMMV infection, could majorly contribute to the resistance to CGMMV infection by regulating nutrient elements and carbohydrate homeostasis. These results provided a novel insight into the molecular mechanism of B-mediated CGMMV suppression and an efficient method of B-application for the improvement of watermelon quality after CGMMV infection.

Heavy metal and metalloid toxicity in horticultural plants: Tolerance mechanism and remediation strategies

Heavy metal/metalloids (HMs) are among the primary soil pollutants that limit crop production worldwide. Plants grown in HM contaminated soils exhibit reduced growth and development, resulting in a decrease in crop production. The exposure to HMs induces plant oxidative stress due to the formation of free radicals, which alter plant morphophysiological and biochemical mechanisms at cellular and tissue levels. When exposed to HM toxicity, plants evolve sophisticated physiological and cellular defense strategies, such as sequestration and transportation of metals, to ensure their survival. Plants also have developed efficient strategies by activating signaling pathways, which induce the expression of HM transporters. Plants either avoid the uptake of HMs from the soil or activate the detoxifying mechanism to tolerate HM stress, which involves the production of antioxidants (enzymatic and non-enzymatic) for the scavenging of reactive oxygen species. The metal-binding proteins including phytochelatins and metallothioneins also participate in metal detoxification. Furthermore, phytohormones and their signaling pathways also help to regulate cellular activities to counteract HM stress. The excessive levels of HMs in the soil can contribute to plant morpho-physiological, biochemical, and molecular alterations, which have a detrimental effect on the quality and productivity of crops. To maintain the commercial value of fruits and vegetables, various measures should be considered to remove HMs from the metal-polluted soils. Bioremediation is a promising approach that involves the use of tolerant microorganisms and plants to manage HMs pollution. The understanding of HM toxicity, signaling pathways, and tolerance mechanisms will facilitate the development of new crop varieties that help in improving phytoremediation.

Zinc Application Mitigates Copper Toxicity by Regulating Cu Uptake, Activity of Antioxidant Enzymes, and Improving Physiological Characteristics in Summer Squash

Zinc (Zn) and copper (Cu) are essential micronutrients for the plant’s growth, development, and metabolism, but in high concentrations, the elements disrupt normal metabolic processes. The present study investigated the effects of different concentrations (added to a Hogland-based solution) of zinc (control, 5, 10 mg L−1 ZnSO4) and copper (control, 0.1, 0.2 mg L−1 CuSO4) on the growth characteristics and biochemical indices of summer squash (Cucurbita pepo L.). Compared with control, a single application of Cu or Zn at both concentrations significantly declined fruit yield, growth traits, pigments content, and high content of these minerals and values of stress-related indices. Increased Cu concentration in the nutritional solutions reduced the activity of ascorbate peroxidase (APX) and guaiacol peroxidase (GPX). Copper at high concentrations intensified ROS production, aggravated oxidative stresses, and decreased the plant yield and productivity. Nonetheless, combining Cu and Zn could alleviate stress intensity by boosting antioxidant enzymes, redox regulation, and a resultant diminishment in the content of H2O2, proline, malondialdehyde, and minerals. The obtained results corroborate that the co-application of zinc in Cu-contaminated areas can improve the plant’s economic yield and physiological parameters by hindering copper toxicity and enhancing the photosynthetic capacity.

Uptake of atmospherically deposited cadmium by leaves of vegetables: Subcellular localization by NanoSIMS and potential risks

Atmospherically deposited cadmium (Cd) may accumulate in plants through foliar uptake; however, the foliar uptake, accumulation, and distribution processes of Cd are still under discussion. Atmospherically deposited Cd was simulated using cadmium sulfide (CdS) with various particle sizes and solubility. Water spinach (Ipomoea aquatica Forsk, WS) and pak choi (Brassica chinensis L., PC) leaves were treated with suspensions of CdS nanoparticles (CdS_N), which entered the leaves via the stomata. Cd concentrations of WS and PC leaves treated with 125 mg L^-1 CdS_N reached up to 39.8 and 11.0 mg kg^-1, respectively, which are higher than the critical leaf concentration for toxicity. Slight changes were observed in fresh biomass, photosynthetic parameters, lipid peroxidation, and mineral nutrient uptake. Exposure concentration, rather than particle size or solubility, regulated the foliar uptake and accumulation of Cd. Subcellular and the high-resolution secondary ion mass spectrometry (NanoSIMS) results revealed that Cd was majorly stored in the soluble fraction and cell walls, which is an important Cd detoxification mechanism in leaves. The potential health risks associated with consuming CdS-containing vegetables were highlighted. These findings facilitate a better understanding of the fate of atmospheric Cd in plants, which is critical in ensuring food security.

A review on bioremediation approach for heavy metal detoxification and accumulation in plants

Nowadays, the accumulation of toxic heavy metals in soil and water streams is considered a serious environmental problem that causes various harmful effects on plants and animals. Phytoremediation is an effective, green, and economical bioremediation approach by which the harmful heavy metals in the contaminated ecosystem can be detoxified and accumulated in the plant. Hyperaccumulators exude molecules called transporters that carry and translocate the heavy metals present in the soil to different plant parts. The hyperaccumulator plant genes can confine higher concentrations of toxic heavy metals in their tissues. The efficiency of phytoremediation relies on various parameters such as soil properties (pH and soil type), organic matters in soil, heavy metal type, nature of rhizosphere, characteristics of rhizosphere microflora, etc. The present review comprehensively discusses the toxicity effect of heavy metals on the environment and different phytoremediation mechanisms for the transport and accumulation of heavy metals from polluted soil. This review gave comprehensive insights into plants tolerance for the higher heavy metal concentration their responses for heavy metal accumulation and the different mechanisms involved for heavy metal tolerance. The current status and the characteristic features that need to be improved in the phytoremediation process are also reviewed in detail.

Heavy metal (loid)s phytotoxicity in crops and its mitigation through seed priming technology

Unexpected bioaccumulation and biomagnification of heavy metal(loid)s (HMs) in the environment have become a predicament for all living organisms, including plants. The presence of these HMs in the plant system raised the level of reactive oxygen species (ROS) and remodeled several vital cellular biomolecules. These lead to several morphological, physiological, metabolic, and molecular aberrations in plants ranging from chlorosis of leaves to the lipid peroxidation of membranes, and degradation of proteins and nucleic acid including the modulation of the enzymatic system, which ultimately affects the plant growth and productivity. Plants are equipped with several mechanisms to counteract the HMs toxicity. Among them, seed priming (SP) technology has been widely tested with the use of several inorganic chemicals, plant growth regulators (PGRs), gasotransmitters, nanoparticles, living organisms, and plant leaf extracts. The use of these compounds has the potential to alleviate the HMs toxicity through the strengthening of the antioxidant defense system, generation of low molecular weight metallothionein's (MTs), and phytochelatins (PCs), and improving seedling vigor during early growth stages. This review presents an account of the sources, uptake and transport, and phytotoxic effects of HMs with special attention to different mechanism/s, occurring to mitigate the HMs toxicity in plants employing SP technology.Novelty statement: To the best of our knowledge, this review has delineated the consequences of HMs on the crucial plant processes, which ultimately affect plant growth and development. This review also compiled the up to dated information on phytotoxicity of HMs through the use of SP technology, this review discussed how different types of SP approaches help in diminishing the concentration HMs in plant systems. Also, we depicted mechanisms, represent how HMs transport and their actions on cellular levels, and emphasized, how diverse SP technology effectiveness in the mitigation of plants' phytotoxicity in unique ways.

Cadmium uptake and transport processes in rice revealed by stable isotope fractionation and Cd-related gene expression

Multiple processes are involved in Cd transfer in rice plants, including root uptake, xylem loading, and immobilization. These processes can be mediated by membrane transporters and can alter Cd speciation by binding Cd to different organic ligands. However, it remains unclear which processes control Cd transport in rice in response to different watering conditions in soil. Herein, Cd isotope fractionation and Cd-related gene expression were employed to investigate the key regulatory mechanisms during uptake, root-to-shoot, and stem-to-leaf transport of Cd in rice grown in pot experiments with Cd-contaminated soil under flooded and non-flooded conditions, respectively. The results showed that soil flooding decreased the Cd concentration in soil porewater and, thereby, Cd uptake and transport in rice. Cd isotopes fractionated negatively from soil porewater to the whole rice (flooded: ∆^114/110Cd_{rice-porewater} = -0.15‰, non-flooded: ∆^114/110Cd_{rice-porewater} = -0.39‰), suggesting that Cd transporters preferentially absorbed light Cd isotopes. The non-flooded treatment revealed an upregulated expression of OsNRAMP1 and OsNRAMP5 genes compared to the flooded treatment, which may partially contribute to its more pronounced porewater-to-rice fractionation. Cd isotopes fractionated positively from roots to shoots under flooded conditions (∆^114/110Cd_shoot-root = 0.19‰). However, a reverse direction of fractionation was observed under non-flooded conditions (∆^114/110Cd_shoot-root = -0.67‰), which was associated with the substantial upregulation of CAL1 in roots, facilitating xylem loading of Cd-CAL1 complexes with lighter isotopes. After being transported to the shoots, the majority of Cd were detained in stems (44%-55%), which were strongly enriched in lighter isotopes than in the leaves (∆^114/110Cd_leaf-stem = 0.77 to 1.01‰). Besides the Cd-CAL1 transported from the roots, the expression of OsPCS1 and OsHMA3 in the stems could also favor the enrichment of Cd-PCs with lighter isotopes, leaving heavier isotopes to be transported to the leaves. The higher expression levels of OsMT1e in older leaves than in younger leaves implied that Cd immobilization via binding to metallothioneins like OsMT1e may favor the enrichment of lighter isotopes in older leaves. The non-flooded treatment showed lighter Cd isotopes in younger leaves than the flooded treatment, suggesting that more Cd-CAL1 in the stems and Cd-PCs in the older leaves might be transported to the younger leaves under non-flooded conditions. Our results demonstrate that isotopically light Cd can be preferentially transported from roots to shoots when more Cd is absorbed by rice under non-flooded conditions, and isotope fractionation signature together with gene expression quantification has the potential to provide a better understanding of the key processes regulating Cd transfer in rice.

Impact of industrial effluents on physico-chemical parameters of water and fatty acid profile of fish, Labeo rohita (Hamilton), collected from the Ramsar sites of Punjab, India

In this contemporary era, wetlands and the entire aquatic diversity are suffering from major pollution problem. Not only the aggregation of higher population in metropolitan causes the production of plenty of solid, liquid and gaseous wastes, but also the high-technological industries contribute to a mammoth of wastes in the ecosystem. During the process of industrial effluent discharge into the water bodies, the toxic substances available in these wastes can affect the aquatic flora and fauna, resultantly disturbing the entire system and constituting human health hazards indirectly or directly. The objective of this study was to estimate the nutritional value of the liver and intestine of fish which is being discarded as waste during fish processing and pollution status by calculated water quality index (WQI) and comparison of both wetlands during diverse seasons. WQI of Harike Wetland was observed to be 56.68 which indicates that water quality in this wetland is "poor", while at Nangal Wetland WQI was calculated to be 39.54 and comes under "good" water quality and safe for the entire ecosystem. HPI (heavy metal pollution index) for Harike Wetland was observed 144.9 and for Nangal Wetland was 3.12, indicating heavy load of heavy metal pollution at test sample site. MI (metal index) value was also detected higher at test sample site (4.76) as compared to that at control site (0.22). The mean total n-3 and n-6 polyunsaturated fatty acids (PUFAs) declined in the liver of test fish samples (Harike Wetland) as compared to control fish (Nangal Wetland) samples except in winter season. Similarly, mean total saturated fatty acids (SFAs) were also found to decline significantly (p<0.05) in the liver of test fish sample as compared to control fish sample during autumn and winter seasons. Significant (p<0.05) decline of mean total n-3 PUFAs (except winter) and total n-6 PUFAs (except rainy) in the intestine of test fish sample was observed during all the seasons when compared to control fish samples. However, total SFAs were found to increase in the intestine of test fish samples as compared to control fish samples during all the studied seasons. In the present investigation, fluctuations recorded in the water quality parameters and major groups of FAs in the tissues were due to the geographical location and pollution load in the fish samples taken from Harike Wetland.

Transfer of Metal(loid)s from Soil to Leaves and Trunk Xylem Sap of Medicinal Plants and Possible Health Risk Assessment

The objective of the present study was to investigate metal(loid)s in soils, in the trunk xylem sap and in the leaves of the Dipteryx alata plant located near the highway with high vehicle traffic in agricultural regions and near landfills, and to assess the transfer of metal(loid)s from soil to plant and possible health risk assessment. Trunk xylem sap, leaves and soil samples were collected at three sites near the highway. The analysis of trace elements was carried out using inductively coupled plasma optical emission spectroscopy (ICP OES). In the three soil sampling sites far from the highway edge, 15 elements were quantified. The concentrations of elements in the soil presented in greater proportions in the distance of 5 m in relation to 20 and 35 m. The metal(loid)s content in the study soil was higher than in other countries. The concentrations of Al, Cu, Fe, Mg, Mn, P, Se and Zn in the xylem sap were much higher than the leaves. The values of transfer factor of P, Mg and Mn from soil to the xylem sap and transfer factor of P from soil to leaf were greater than 1, indicating that the specie have a significant phytoremediation and phytoextraction potential. This plant has a tendency to accumulate As, Cd and Cr in its leaf tissues. The chronic hazard index (HI) values recorded in this study were above 1 for adults and adolescents. It is concluded that the soil, the trunk xylem sap and leaves of this plant are contaminated by heavy metals. Ingestion of the trunk xylem sap of this plant can cause toxicity in humans if ingested in large quantities and in the long term; therefore, its consumption should be avoided.

Genetic biofortification of wheat with zinc: Opportunities to fine-tune zinc uptake, transport and grain loading

Zinc (Zn) is an important micronutrient in the human body, and health complications associated with insufficient dietary intake of Zn can be overcome by increasing the bioavailable concentrations in edible parts of crops (biofortification). Wheat (Triticum aestivum L) is the most consumed cereal crop in the world; therefore, it is an excellent target for Zn biofortification programs. Knowledge of the physiological and molecular processes that regulate Zn concentration in the wheat grain is restricted, inhibiting the success of genetic Zn biofortification programs. This review helps break this nexus by advancing understanding of those processes, including speciation regulated uptake, root to shoot transport, remobilisation, grain loading and distribution of Zn in wheat grain. Furthermore, new insights to genetic Zn biofortification of wheat are discussed, and where data are limited, we draw upon information for other cereals and Fe distribution. We identify the loading and distribution of Zn in grain as major bottlenecks for biofortification, recognising anatomical barriers in the vascular region at the base of the grain, and physiological and molecular restrictions localised in the crease region as major limitations. Movement of Zn from the endosperm cavity into the modified aleurone, aleurone and then to the endosperm is mainly regulated by ZIP and YSL transporters. Zn complexation with phytic acid in the aleurone limits Zn mobility into the endosperm. These insights, together with synchrotron-X-ray-fluorescence microscopy, support the hypothesis that a focus on the mechanisms of Zn loading into the grain will provide new opportunities for Zn biofortification of wheat.

Functions and strategies for enhancing zinc availability in plants for sustainable agriculture

Zinc (Zn), which is regarded as a crucial micronutrient for plants, and is considered to be a vital micronutrient for plants. Zn has a significant role in the biochemistry and metabolism of plants owing to its significance and toxicity for biological systems at specific Zn concentrations, i.e., insufficient or harmful above the optimal range. It contributes to several cellular and physiological activities of plants and promotes plant growth, development, and yield. Zn is an important structural, enzymatic, and regulatory component of many proteins and enzymes. Consequently, it is essential to understand the interplay and chemistry of Zn in soil, its absorption, transport, and the response of plants to Zn deficiency, as well as to develop sustainable strategies for Zn deficiency in plants. Zn deficiency appears to be a widespread and prevalent issue in crops across the world, resulting in severe production losses that compromise nutritional quality. Considering this, enhancing Zn usage efficiency is the most effective strategy, which entails improving the architecture of the root system, absorption of Zn complexes by organic acids, and Zn uptake and translocation mechanisms in plants. Here, we provide an overview of various biotechnological techniques to improve Zn utilization efficiency and ensure the quality of crop. In light of the current status, an effort has been made to further dissect the absorption, transport, assimilation, function, deficiency, and toxicity symptoms caused by Zn in plants. As a result, we have described the potential information on diverse solutions, such as root structure alteration, the use of biostimulators, and nanomaterials, that may be used efficiently for Zn uptake, thereby assuring sustainable agriculture.

Characterization of cadmium accumulation in the cell walls of leaves in a low-cadmium rice line and strengthening by foliar silicon application

Cadmium (Cd) remobilization in leaves is affected by whether Cd is stored in nonlabile subcellular compartments, which might be regulated by silicon (Si) application. However, the underlying mechanism is still far from being completely understood. In this research, the Cd distribution pattern in leaves and a Cd-binding characterization in the cell wall of the low-Cd rice line YaHui2816 were investigated through one hydroponic experiment with 10 μM Cd in solutions. Foliar Si application was further adopted to explore its influence on the Cd accumulation in the cell walls of leaves in YaHui2816. Most of the Cd (69.4%) was distributed in the cell walls of YaHui2816 leaves, whereas the isolated cell walls of leaves from YaHui2816 exhibited a lower capacity for Cd chemisorption than the contrasting line C268A, which was resulted from its fewer relative peak areas of functional groups in the cell wall, such as carboxyl CO and OH stretching. Foliar Si application significantly increased the Cd concentration in leaves and various cell wall fractions (pectin, hemicellulose 1 and residue) by 191% and 137-160%, respectively. RNA-seq analysis revealed that foliar Si application depressed the expression of the metal transporters OsZIP7 and OsZIP8, up-regulated the expression of genes participating in the glutathione metabolism and the cellulose synthesis. Overall, the influence of foliar Si application on Cd-accumulation in the cell wall of leaves in a low-Cd rice line was demonstrated in this research, which inspires further avenues to ensure the food safety of rice grains.

Activation of antioxidative and detoxificative systems in Brassica juncea L. plants against the toxicity of heavy metals

Plant metal hyperaccumulators, to which Brassica juncea belongs, must have very efficient defence mechanisms that enable growth and development in an environment polluted with various heavy metals. B. juncea (Indiana mustard) v. Małopolska was exposed to the activity of trace elements such as cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in combinations: CuPb, CuCd, CuZn, PbCd, PbZn, and ZnCd in a concentration of 25 μM each for 96 h during control cultivation. We observed a clear tendency for metal uptake and accumulation in above-ground parts which is characteristic of hyperaccumulators. The combinations of CuCd, CuZn, and PbCd inhibited the development of the seedlings the most. The used metal combinations increased the levels of reactive oxygen species (ROS) such as: hydrogen peroxide (H₂O₂), superoxide anion (O₂^.-) and oxidized proteins in B. juncea organs, generating oxidative stress conditions in the cells. We determined the level of transcription of the respective defence proteins of the detoxification and antioxidant systems. We have shown that in the first 24 h of stress condiction, activation of glutamylcysteine-γ synthetase (yECS) and glutathione reductase (GR1) enzymes related to the detoxification of heavy metals is important for B. juncea plants. In addition, the data provide important information on how plants respond to the presence of heavy metals in the first days of stress conditions.

PDF1.5 Enhances Adaptation to Low Nitrogen Levels and Cadmium Stress

Environmental acclimation ability plays a key role in plant growth, although the mechanism remains unclear. Here, we determined the involvement of Arabidopsis thaliana PLANT DEFENSIN 1 gene AtPDF1.5 in the adaptation to low nitrogen (LN) levels and cadmium (Cd) stress. Histochemical analysis revealed that AtPDF1.5 was mainly expressed in the nodes and carpopodium and was significantly induced in plants exposed to LN conditions and Cd stress. Subcellular localization analysis revealed that AtPDF1.5 was cell wall- and cytoplasm-localized. AtPDF1.5 overexpression significantly enhanced adaptation to LN and Cd stress and enhanced the distribution of metallic elements. The functional disruption of AtPDF1.5 reduced adaptations to LN and Cd stress and impaired metal distribution. Under LN conditions, the nitrate transporter AtNRT1.5 expression was upregulated. Nitrate transporter AtNRT1.8 expression was downregulated when AtPDF1.5 was overexpressed, resulting in enhanced transport of NO₃^- to shoots. In response to Cd treatment, AtPDF1.5 regulated the expression of metal transporter genes AtHMP07, AtNRAMP4, AtNRAMP1, and AtHIPP3, resulting in higher Cd accumulation in the shoots. We conclude that AtPDF1.5 is involved in the processing or transmission of signal substances and plays an important role in the remediation of Cd pollution and LN adaptation.

Isotopic signatures reveal zinc cycling in the natural habitat of hyperaccumulator Dichapetalum gelonioides subspecies from Malaysian Borneo

BACKGROUND

Some subspecies of Dichapetalum gelonioides are the only tropical woody zinc (Zn)-hyperaccumulator plants described so far and the first Zn hyperaccumulators identified to occur exclusively on non-Zn enriched 'normal' soils. The aim of this study was to investigate Zn cycling in the parent rock-soil-plant interface in the native habitats of hyperaccumulating Dichapetalum gelonioides subspecies (subsp. pilosum and subsp. sumatranum). We measured the Zn isotope ratios (δ66Zn) of Dichapetalum plant material, and associated soil and parent rock materials collected from Sabah (Malaysian Borneo).

RESULTS

We found enrichment in heavy Zn isotopes in the topsoil (δ66Zn 0.13 ‰) relative to deep soil (δ66Zn -0.15 ‰) and bedrock (δ66Zn -0.90 ‰). This finding suggests that both weathering and organic matter influenced the Zn isotope pattern in the soil-plant system, with leaf litter cycling contributing significantly to enriched heavier Zn in topsoil. Within the plant, the roots were enriched in heavy Zn isotopes (δ66Zn ~ 0.60 ‰) compared to mature leaves (δ66Zn ~ 0.30 ‰), which suggests highly expressed membrane transporters in these Dichapetalum subspecies preferentially transporting lighter Zn isotopes during root-to-shoot translocation. The shoots, mature leaves and phloem tissues were enriched in heavy Zn isotopes (δ66Zn 0.34-0.70 ‰) relative to young leaves (δ66Zn 0.25 ‰). Thisindicates that phloem sources are enriched in heavy Zn isotopes relative to phloem sinks, likely because of apoplastic retention and compartmentalization in the Dichapetalum subspecies.

CONCLUSIONS

The findings of this study reveal Zn cycling in the rock-soil-plant continuum within the natural habitat of Zn hyperaccumulating subspecies of Dichapetalum gelonioides from Malaysian Borneo. This study broadens our understanding of the role of a tropical woody Zn hyperaccumulator plant in local Zn cycling, and highlights the important role of leaf litter recycling in the topsoil Zn budget. Within the plant, phloem plays key role in Zn accumulation and redistribution during growth and development. This study provides an improved understanding of the fate and behaviour of Zn in hyperaccumulator soil-plant systems, and these insights may be applied in the biofortification of crops with Zn.

Physiological and molecular mechanisms of metal accumulation in hyperaccumulator plants

Most of the heavy metals (HMs), and metals/metalloids are released into the nature either by natural phenomenon or anthropogenic activities. Being sessile organisms, plants are constantly exposed to HMs in the environment. The metal non-hyperaccumulating plants are susceptible to excess metal concentrations. They tend to sequester metals in their root vacuoles by forming complexes with metal ligands, as a detoxification strategy. In contrast, the metal-hyperaccumulating plants have adaptive intrinsic regulatory mechanisms to hyperaccumulate or sequester excess amounts of HMs into their above-ground tissues rather than accumulating them in roots. They have unique abilities to successfully carry out normal physiological functions without showing any visible stress symptoms unlike metal non-hyperaccumulators. The unique abilities of accumulating excess metals in hyperaccumulators partly owes to constitutive overexpression of metal transporters and ability to quickly translocate HMs from root to shoot. Various metal ligands also play key roles in metal hyperaccumulating plants. These metal hyperaccumulating plants can be used in metal contaminated sites to clean-up soils. Exploiting the knowledge of natural populations of metal hyperaccumulators complemented with cutting-edge biotechnological tools can be useful in the future. The present review highlights the recent developments in physiological and molecular mechanisms of metal accumulation of hyperaccumulator plants in the lights of metal ligands and transporters. The contrasting mechanisms of metal accumulation between hyperaccumulators and non-hyperaccumulators are thoroughly compared. Moreover, uses of different metal hyperaccumulators for phytoremediation purposes are also discussed in detail.

Functional and molecular characterization of fluoride exporter (FEX) from rice and its constitutive overexpression in Nicotiana benthamiana to promote fluoride tolerance

KEY MESSAGE

Early induction of OsFEX was insufficient for fluoride adaptation in IR-64. Overexpression of OsFEX in yeast and Nicotiana benthamiana enhanced fluoride tolerance. The present study delineates the regulation of fluoride exporter (FEX) in the fluoride-sensitive rice cultivar, IR-64 and its efficacy in generating high fluoride tolerance in transgenic Nicotiana benthamiana. Gene and protein expression profiling revealed that OsFEX exhibited early induction during fluoride stress in the vegetative and reproductive tissues of IR-64, although the expression was suppressed upon prolonged stress treatment. Analysis of OsFEX promoter in transgenic N. benthamiana, using β-glucuronidase reporter assay confirmed its early inducible nature, since the reporter expression and activity peaked at 12 h of NaF stress, after which it was lowered. OsFEX expression was up regulated in the presence of gibberellic acid (GA) and melatonin, while it was suppressed by abscisic acid (ABA). Complementation of ΔFEX1ΔFEX2 yeast mutants with OsFEX enabled high fluoride tolerance, thus validating the functional efficiency of the transgene. Bioassay of transgenic N. benthamiana lines, expressing OsFEX either under its own promoter or under CaMV35S promoter, established that constitutive overexpression, rather than early induction of OsFEX was essential and crucial for generating fluoride tolerance in the transgenics. Overall, the suppression of OsFEX in the later growth phases of stressed IR-64 due to enhanced ABA conservation and lowered synthesis of GA, as supported by the application of the respective phytohormone biosynthetic inhibitors, such as sodium tungstate and paclobutrazol, accounted for the fluoride-hyperaccumulative nature of the rice cultivar.

Biophenolic Profile Modulations in Olive Tissues as Affected by Manganese Nutrition

Manganese (Mn) is an essential element that intervenes in several plant metabolic processes. The olive tree, and its fruits and leaves, are known as a source of nutraceuticals since they are rich in biophenols. However, there is still a serious lack of data about biophenolic distribution in olive stems and roots under Mn fertilisation. In this context, our study aimed to examine the effects of Mn fertilisation on the biophenolic profile in the leaves, stems, and roots of the ‘Istarska bjelica’ olive cultivar. The experiment was set up in a greenhouse, during a period of five months, as a random block design consisting of three treatments with varying Mn concentrations in full-strength Hoagland’s nutrient solution (0.2 µM Mn, 12 µM Mn, and 24 µM Mn). The obtained results indicate that the amount of Mn in the examined olive plant tissues was significantly higher under 12 µM Mn and 24 µM Mn treatments compared to that of the 0.2 µM Mn treatment. While the concentration of biophenols varied in roots depending on the compound in question, a strong positive impact of the increased Mn concentration in nutrient solution (12 µM Mn and 24 µM Mn) on the concentrations of the main biophenolic compounds was observed in stems. The concentration of oleuropein in leaves almost doubled at 24 µM Mn, with the highest Mn concentration, as compared to the 0.2 µM Mn treatment. The obtained results led to the conclusion that the supply of Mn could enhance the concentration of some biologically active compounds in olives grown hydroponically, implying a critical need for further investigation of Mn fertilisation practices in the conventional olive farming system.

Effects of soil amendments on leaf anatomical characteristics of marigolds cultivated in cadmium-spiked soils

The marigolds (Tagetes spp.) in this study were classified as excluders for cadmium (Cd); however, their leaves also accumulated substantial Cd content. Among the experimental treatments (i.e., control, cattle manure, pig manure, and leonardite which served as soil amendments), pig manure resulted in significantly increased growth performance for all marigold cultivars as seen by relative growth rates (119-132.3%) and showed positive effects on leaf anatomy modifications, e.g., thickness of spongy and palisade mesophyll, size of vein area and diameter of xylem cells. This may be due to substantially higher essential nutrient content, e.g., total nitrogen (N) and extractable phosphorus (P), in pig manure that aided all marigold cultivars, particularly the French cultivar which exhibited the highest relative growth rate (132.3%). In the Cd-only treatment, cell disorganization was observed in vascular bundles as well as in palisade and spongy mesophyll, which may have been responsible for the lowest plant growth performance recorded in this study, particularly among the American and Honey cultivars (RGR = 73% and 77.3%, respectively).

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

Phytoremediation of electroplating wastewater by vetiver grass (Chrysopogon zizanoides L.)

The electroplating industry generates wastewater containing a variety of heavy metals which potentially contaminate water ecosystems. The available and well-known electroplating wastewater treatments are considered as an expensive and less effective method, therefore phytoremediation was used as an alternative friendly solution. This study aims to evaluate the uptake and elimination rate of heavy metals by vetiver (Chrysopogon zizanoides L.) on metal-polluted water. Vetiver was planted in artificial electroplating wastewater containing different levels (low, medium, high) of chromium (Cr) and nickel (Ni). Water, roots, and shoots were collected periodically to determine Cr and Ni contents using Atomic Absorption Spectrometry (AAS). Metal accumulation and elimination rate, Bioconcentration Factor (BCF), Biological Absorption Coefficient (BAC), and Translocation Factor (TF) were calculated to evaluate plant's effectiveness in metal remediation processes. The results showed that vetiver (C. zizanoides L.) was able to remove 61.10% Cr and 95.65% Ni on metal-contaminated water. The highest uptake rates for Cr and Ni are 127.21 mg/kg/day and 15.60 mg/kg/day respectively, while the elimination rates for Cr and Ni tend to slow 1.09 mg/kg/day and 12.24 mg/kg/day respectively. Vetiver BCF, BAC, and TF values on Cr and Ni contaminated water were greater than 1, which indicates that vetiver work through phytoextraction and phytostabilization to treat metals. The findings showed that vetiver has promise as a phytoremediation agent thus providing implication for electroplating wastewater treatment.