Effects of cadmium stress on growth and amino acid metabolism in two Compositae plants

Bioactive metabolite profiles and quality of Rosa rugosa during its growing and flower-drying process

Rosa rugosa is extensively cultivated in China for its remarkable fragrance and flavor, however, the metabolic changes in roses during growth and drying remain unclear. Our results revealed significant variations in phenol and flavonoid contents and antioxidant capacity in roses (Rosa rugosa f. plena (Regel) Byhouwer) under different conditions. Phenol contents were positively correlated with antioxidant capacity, with phytochemicals being most prominent in unfolded petals. The highest antioxidant capacity and phenol and flavonoid contents were observed in April. Considering their greater consumption value, whole flowers were more suitable than petals alone. Furthermore, considerable sensory and nutritional differences were observed in dried roses. Different drying methods increased their total phenol content of roses by 4.2-5.4 times and the antioxidant capacity by 2.9 times. Metabolomics revealed the altered contents of flavonoids, anthocyanins, lipids, amino acids, and saccharides. This study provides baseline data for the potential of roses as a natural source of antioxidants in the food and pharmaceutical industries.

Microplastics alter cadmium accumulation in different soil-plant systems: Revealing the crucial roles of soil bacteria and metabolism

Cadmium (Cd) and microplastics (MPs) gradually increased to be prevalent contaminants in soil, it is important to understand their combined effects on different soil-plant systems. We studied how different doses of polylactic acid (PLA) and polyethylene (PE) affected Cd accumulation, pakchoi growth, soil chemical and microbial properties, and metabolomics in two soil types. We found that high-dose MPs decreased Cd accumulation in plants in red soil, while all MPs decreased Cd bioaccumulation in fluvo-aquic soil. This difference was primarily attributed to the increase in dissolved organic carbon (DOC) and pH in red soil by high-dose MPs, which inhibited Cd uptake by plant roots. In contrast, MPs reduced soil nitrate nitrogen and available phosphorus, and weakened Cd mobilization in fluvo-aquic soil. In addition, high-dose PLA proved detrimental to plant health, manifesting in shortened shoot and root lengths. Co-exposure of Cd and MPs induced the shifts in bacterial populations and metabolites, with specific taxa and metabolites closely linked to Cd accumulation. Overall, co-exposure of Cd and MPs regulated plant growth and Cd accumulation by driving changes in soil bacterial community and metabolic pathways caused by soil chemical properties. Our findings could provide insights into the Cd migration in different soil-plant systems under MPs exposure. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) and cadmium (Cd) are common pollutants in farmland soil. Co-exposure of MPs and Cd can alter Cd accumulation in plants, and pose a potential threat to human health through the food chain. Here, we investigated the effects of different types and doses of MPs on Cd accumulation, plant growth, soil microorganisms, and metabolic pathways in different soil-plant systems. Our results can contribute to our understanding of the migration and transport of Cd by MPs in different soil-plant systems and provide a reference for the control of combined pollution in the future research.

The effect of biofertilizers on nickel accumulation, nitrogen metabolism and amino acid profile of corn (Zea mays L.) exposed to nickel stress

The issue of heavy metal pollution such as nickel poses a significant environmental concern, exerting detrimental effects on the growth and viability of plant life. Plants have various mechanisms to effectively manage heavy metal stress, including the ability to modify their amino acid type and content. This adaptive response allows plants to mitigate the detrimental effects caused by excessive heavy metal accumulation. The aim of this study was to investigate the effect of biofertilizers on nickel accumulation, nitrogen metabolism and amino acid profile of corn (Zea mays L.) cv. 'PL438' exposed to Ni stress. After disinfecting and soaking in water for 24 h, corn seeds were primed with bacterial biofertilizers (T2: NPK + FZ), fungal biofertilizers (T3: Arbuscular mycorrhizal fungi (AMF) + Trichoderma (T)), or a combination of them (T4: NPK + FZ + AMF + T) and were cultured by the hydroponic method in completely controlled conditions. Then, they were simultaneously exposed to nickel chloride at various rates (0, 75, or 150 µM) at the three-leaf stage. They were harvested two weeks later and were subjected to the measurement of Ni content, nitrate and nitrite content, nitrate reductase activity, and amino acid profile by high-performance liquid chromatography. The results showed that the application of Ni at higher rates increased Ni, nitrate, and nitrite contents and nitrate reductase activity. The study of Ni accumulation and TF revealed that Ni accumulated in the roots to a greater extent than in the shoots and TF was < 1 in all treatments. The shoot amino acid profile showed that the treatment of Ni+2 increased som amino acids such as aspartic acid, asparagine, serine, histidine, and glycine versus the control, whereas T4 Ni+2 increased aspartic acid, glutamic acid, threonine and arginine. The change in amino acids in Ni-treated plants may play a key role in their adaptation to Ni stress. The findings indicate that biofertilizers played a crucial role in mitigating the negative impacts of Ni on corn plants through alterations in amino acid composition and decreased absorption and translocation of Ni.

Transcriptome sequencing analysis of gene expression in phosphate-solubilizing bacterium 'N3' and grafted watermelon plants coping with toxicity induced by cadmium

Cadmium (Cd) is a harmful metal in soil, and reducing Cd accumulation in plants has become a vital prerequisite for maintaining food safety. Phosphate-solubilizing bacteria (PSB) can not only improve plant growth but also inhibit the transportation of metals to roots. However, data on gene expression in PSB Burkholderia sp. strain 'N3' and grafted watermelon plants dealing with Cd remain to be elucidated. In this study, core genes and metabolic pathways of strain 'N3' and grafted plants were analyzed by Illumina sequencing. Results showed that 356 and 2527 genes were upregulated in 'N3' and grafted watermelon plants, respectively, whereas 514 and 1540 genes were downregulated in 'N3' and grafted watermelon plants, respectively. Gene ontology enrichment analysis showed that signal transduction, inorganic ion transport, cell motility, amino acid transport, and metabolism pathways were marked in 'N3'. However, pathways such as secondary metabolite biosynthesis, oxidation-reduction process, electron transfer activity, and channel regulator activity were marked in the grafted plants. Six genes related to pentose phosphate, glycolysis, and gluconeogenesis metabolism were upregulated in the grafted plants. This study paves the way for developing potential strategies to improve plant growth under Cd toxicity.

Inhibition of microelement accumulation and disorder of saccharide and amino acid metabolism explain rice grain empty under dimethylarsinic acid stress

KEY MESSAGE

Metabolomic and transcriptomic analyses revealed an intensification of energy metabolism in rice grains under DMA stress, possibly causing the consumption of sugars or non-sugars and the development of unfilled grains Excessive dimethylarsinic acid (DMA) causes rice straighthead disease, a physiological disorder typically with erect panicle due to empty grain at maturity. Although the toxicity of DMA and its uptake and transport in rice are well recognized, the underlying mechanism of unfilled grains remains unclear. Therefore, a pot experiment was conducted using a susceptible variety (Ruanhuayou1179, RHY) and a resistant one (Nanjingxiangzhan, NJXZ) via the metabolomic and transcriptomic approaches to explore the mechanisms of empty grains in diseased rice under DMA stress. The results demonstrate an increase in total and methylated As in grains of RHY and NJXZ under DMA addition, with RHY containing higher levels of DMA. DMA addition increased the soluble sugar content in grains of RHY and NJXZ by 17.1% and 14.3% compared to the control, respectively, but significantly reduced the levels of amino acid, soluble protein, and starch. The decrease of grain Zn and B contents was also observed, and inadequate Zn might be a key factor limiting rice grain yield under DMA stress. Notably, DMA addition altered the expression levels of genes involved in the transport of sugar, amino acids, nitrates/peptides, and mineral ions. In sugar and amino acid metabolism, the reduction of metabolites and the upregulated expression of genes reflect positive regulation at the level of energy metabolism, implying that the reduction of grain starch and proteins might be ascribed to generate sufficient energy to resist the stress. This study provides a useful reference for understanding the molecular mechanism of grain emptying under DMA stress.

Conjoint analysis of physio-biochemical, transcriptomic, and metabolomic reveals the response characteristics of solanum nigrum L. to cadmium stress

Cadmium (Cd) is a nonessential element in plants and has adverse effects on the growth and development of plants. However, the molecular mechanisms of Cd phytotoxicity, tolerance and accumulation in hyperaccumulators Solanum nigrum L. has not been well understood. Here, physiology, transcriptome, and metabolome analyses were conducted to investigate the influence on the S. nigrum under 0, 25, 50, 75 and 100 µM Cd concentrations for 7 days. Pot experiments demonstrated that compared with the control, Cd treatment significantly inhibited the biomass, promoted the Cd accumulation and translocation, and disturbed the balance of mineral nutrient metabolism in S. nigrum, particularly at 100 µM Cd level. Moreover, the photosynthetic pigments contents were severely decreased, while the content of total protein, proline, malondialdehyde (MDA), H2O2, and antioxidant enzyme activities generally increased first and then slightly declined with increasing Cd concentrations, in both leaves and roots. Furthermore, combined with the previous transcriptomic data, numerous crucial coding-genes related to mineral nutrients and Cd ion transport, and the antioxidant enzymes biosynthesis were identified, and their expression pattern was regulated under different Cd stress. Simultaneously, metabolomic analyses revealed that Cd treatment significantly changed the expression level of many metabolites related to amino acid, lipid, carbohydrate, and nucleotide metabolism. Metabolic pathway analysis also showed that S. nigrum roots activated some differentially expressed metabolites (DEMs) involved in energy metabolism, which may enhance the energy supply for detoxification. Importantly, central common metabolism pathways of DEGs and DEMs, including the "TCA cycle", "glutathione metabolic pathway" and "glyoxylate and dicarboxylate metabolism" were screened using conjoint transcriptomics and metabolomics analysis. Our results provide some novel evidences on the physiological and molecular mechanisms of Cd tolerance in hyperaccumulator S. nigrum plants.

Multicontamination Toxicity Evaluation in the Model Plant Lactuca sativa L

Many contaminated soils contain several toxic elements (TEs) in elevated contents, and plant-TE interactions can differ from single TE contamination. Therefore, this study investigated the impact of combined contamination (As, Cd, Pb, Zn) on the physiological and metabolic processes of lettuce. After 45 days of exposure, TE excess in soil resulted in the inhibition of root and leaf biomass by 40 and 48%, respectively. Oxidative stress by TE accumulation was indicated by markers-malondialdehyde and 5-methylcytosine-and visible symptoms of toxicity (leaf chlorosis, root browning) and morpho-anatomical changes, which were related to the change in water regime (water potential decrease). An analysis of free amino acids (AAs) indicated that TEs disturbed N and C metabolism, especially in leaves, increasing the total content of free AAs and their families. Stress-induced senescence by TEs suggested changes in gas exchange parameters (increase in transpiration rate, stomatal conductance, and intercellular CO2 concentration), photosynthetic pigments (decrease in chlorophylls and carotenoids), a decrease in water use efficiency, and the maximum quantum yield of photosystem II. These results confirmed that the toxicity of combined contamination significantly affected the processes of lettuce by damaging the antioxidant system and expressing higher leaf sensitivity to TE multicontamination.

New Insights into MeHg Accumulation in Rice (Oryza sativa L.): Evidence from Cysteine

The intake of methylmercury (MeHg)-contaminated rice poses immense health risks to rice consumers. However, the mechanisms of MeHg accumulation in rice plants are not entirely understood. The knowledge that the MeHg-Cysteine complex was dominant in polished rice proposed a hypothesis of co-transportation of MeHg and cysteine inside rice plants. This study was therefore designed to explore the MeHg accumulation processes in rice plants by investigating biogeochemical associations between MeHg and amino acids. Rice plants and underlying soils were collected from different Hg-contaminated sites in the Wanshan Hg mining area. The concentrations of both MeHg and cysteine in polished rice were higher than those in other rice tissues. A significant positive correlation between MeHg and cysteine in rice plants was found, especially in polished rice, indicating a close geochemical association between cysteine and MeHg. The translocation factor (TF) of cysteine showed behavior similar to that of the TF of MeHg, demonstrating that these two chemical species might share a similar transportation mechanism in rice plants. The accumulation of MeHg in rice plants may vary due to differences in the molar ratios of MeHg to cysteine and the presence of specific amino acid transporters. Our results suggest that cysteine plays a vital role in MeHg accumulation and transportation inside rice plants.

A review of artificial intelligence-assisted omics techniques in plant defense: current trends and future directions

Plants intricately deploy defense systems to counter diverse biotic and abiotic stresses. Omics technologies, spanning genomics, transcriptomics, proteomics, and metabolomics, have revolutionized the exploration of plant defense mechanisms, unraveling molecular intricacies in response to various stressors. However, the complexity and scale of omics data necessitate sophisticated analytical tools for meaningful insights. This review delves into the application of artificial intelligence algorithms, particularly machine learning and deep learning, as promising approaches for deciphering complex omics data in plant defense research. The overview encompasses key omics techniques and addresses the challenges and limitations inherent in current AI-assisted omics approaches. Moreover, it contemplates potential future directions in this dynamic field. In summary, AI-assisted omics techniques present a robust toolkit, enabling a profound understanding of the molecular foundations of plant defense and paving the way for more effective crop protection strategies amidst climate change and emerging diseases.

Combined Proteomic and Metabolomic Analyses Reveal the Comprehensive Regulation of Stropharia rugosoannulata Mycelia Exposed to Cadmium Stress

The potential of Stropharia rugosoannulata as a microbial remediation material for cadmium (Cd)-contaminated soil lies in its capacity to absorb and accumulate Cd in its mycelia. This study utilized the TMT and LC-MS techniques to conduct integrated proteomic and metabolomic analyses with the aim of investigating the mycelial response mechanisms of S. rugosoannulata under low- and high-Cd stresses. The results revealed that mycelia employed a proactive defense mechanism to maintain their physiological functions, leading to reduced sensitivity to low-Cd stress. The ability of mycelia to withstand high levels of Cd stress was influenced primarily by the comprehensive regulation of six metabolic pathways, which led to a harmonious balance between nitrogen and carbohydrate metabolism and to reductions in oxidative stress and growth inhibition caused by Cd. The results provide valuable insights into the molecular mechanisms involved in the response of S. rugosoannulata mycelia to Cd stress.

Soil inorganic amendments produce safe rice by reducing the transfer of Cd and increasing key amino acids in brown rice

The digestibility of cadmium (Cd) in brown rice is directly related to amino acid metabolism in rice and human health. In our field study, three kinds of alkaline calcium-rich soil inorganic amendments (SIAs) at three dosages were applied to produce safe rice and improve the quality of rice in Cd-contaminated paddy. With the increased application of SIA, Cd content in iron plaque on rice root significantly increased, the transfer of Cd from rice root to grain significantly decreased, and then Cd content in brown rice decreased synchronously. The vitro digestibility of Cd in brown rice was estimated by a physiologically based extraction test. Results showed that more than 70% of Cd in brown rice could be digested by simulated gastrointestinal juice. Based on the total and digestible Cd contents in brown rice to evaluate the health risk, the application of 2.25 ton SIA/ha could produce safe rice in acidic slightly Cd-contaminated paddy soils. The amino acids (AAs) in brown rice were determined by high-performance liquid chromatography. The contents of 5 key AAs (KAAs) that actively respond to environmental changes increased significantly with the increased application of SIA. The structural equation model indicated that KAAs could be affected by the Cd translocation capacity from rice root to grain, and consequently altered the ratio of indigestible Cd in brown rice. The formation of indigestible KAAs-Cd complexes by combining KAAs (phenylalanine, leucine, histidine, glutamine, and asparagine) with Cd in brown rice could be considered a potential mechanism for reducing the digestibility of Cd.

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.

Red light alleviates Cd toxicity in Egeria densa by modifying carbon-nitrogen metabolism and boosting energy metabolism

Among the various pollutants detected in aquatic ecosystems, cadmium (Cd) is considered as one of the most hazardous. Freshwater macrophytes have been recognized as possible candidates for eliminating Cd from environment. Nevertheless, the impact of light quality on their ability to tolerate Cd toxicity remains unclear, and the underlying mechanisms have yet to be fully elucidated. In this study, we utilized physiological testing and metabolomics to explore the potential mechanisms by which light quality influences the ability of Egeria densa, a significant Cd hyperaccumulator, to withstand Cd toxicity. The study demonstrated that following Cd treatment, E. densa grown under red light exhibited superior photosynthetic efficiency compared to those grown under blue light, as evidenced by significantly increased photosynthetic rate, higher starch content, and greater activity of photosynthetic enzymes. Moreover, metabolomic analyses revealed that under Cd stress, E. densa grown under red light exhibited an enhanced glycolysis for increased energy production. Sucrose metabolism was also improved to generate sufficient sugar including glucose, fructose and mannose for osmotic adjustment. Moreover, under red light, the heightened production of α-ketoglutarate via tricarboxylic acid (TCA) cycle redirected nitrogen flow towards the synthesis of resilient substances such as γ-Aminobutyric Acid (GABA) and methionine. The production of these substances was ∼2.0 and 1.3 times greater than that of treatment with Cd under blue light, thereby improving E. densa's capacity to withstand Cd stress. This study represents the initial investigation into the possible mechanisms by which light quality influences the ability of E. densa to withstand Cd toxicity through regulating CN metabolism. Furthermore, these findings have the potential to improve phytoremediation strategies aimed at reducing Cd pollution.

Response of Carrot (Daucus carota L.) to Multi-Contaminated Soil from Historic Mining and Smelting Activities

A pot experiment was undertaken to investigate the effect of Cd, Pb and Zn multi-contamination on the physiological and metabolic response of carrot (Daucus carota L.) after 98 days of growth under greenhouse conditions. Multi-contamination had a higher negative influence on leaves (the highest Cd and Zn accumulation) compared to the roots, which showed no visible change in terms of anatomy and morphology. The results showed the following: (i) significantly higher accumulation of Cd, Zn, and Pb in the multi-contaminated variant (Multi) compared to the control; (ii) significant metabolic responses-an increase in the malondialdehyde content of the Multi variant compared to the control in the roots (by 20%), as well as in the leaves (by 53%); carotenoid content in roots decreased by 31% in the Multi variant compared with the control; and changes in free amino acids, especially those related to plant stress responses. The determination of hydroxyproline and sarcosine may reflect the higher sensitivity of carrot leaves to multi-contamination in comparison to roots. A similar trend was observed for the content of free methionine (significant increase of 31% only in leaves); (iii) physiological responses (significant decreases in biomass, changes in gas-exchange parameters and chlorophyll a); and (iv) significant changes in enzymatic activities (chitinase, alanine aminopeptidase, acid phosphatase) in the root zone.

A new quantitative insight: Interaction of polyethylene microplastics with soil - microbiome - crop

In this study, the interaction between primary/secondary PE MPs and soil - microbiome - crop complex system and PE MPs enrichment behavior in crops were studied by using the self-developed quantitative characterization method of Eu-MPs and in situ zymography. The results demonstrated for the first time the enrichment effect of micron-sized PE (> 10 µm) in crops, manifested as roots>leaves>stems. Primary PE MPs significantly increased soil TN, TC, SOM and β-glu activity and inhibited Phos activity. Age-PE MPs significantly reduced soil TN, TP, β-glu and Phos activities and also have significant inhibitory effects on plant height, stem diameter, and leaf dry weight of maize. Age-PE MPs significantly affected soil microbial diversity, mainly caused by bacterial genera such as UTCFX1, Sphingomonas, Subgroup-6 and Gemmatimonas. Age-PE MPs also affected some metabolism related to microbial community composition and maize growth, including Glycerolipid, Citrate cycle (TCA cycle), C5-Branched dibasic acid, Arginine and proline, Tyrosine metabolism, pentose phosphate pathway, Valine, leucine and isoleucine biosynthesis. These research results indicated that the PE MPs, which are widely present in farmland soils, can affect crop growth, soil microbial community and metabolic function after aging, thus affecting agroecosystems and terrestrial biodiversity.

Leaf proteomic profiles in cacao scion-rootstock combinations tolerant and intolerant to cadmium toxicity

Cd contamination in cacao beans is one of the major problems faced by cocoa producing countries in Latin America. Cacao scion-rootstock combinations influence the Cd accumulation in the shoot of the plant. The objective of this work was to carry out a comparative analysis between cacao scion rootstock combinations (CCN 51/BN 34, CCN 51/PS 13.19, CCN 51/PH 16 and CCN 51/CCN 51), contrasting for tolerance to cadmium (Cd) toxicity, by means of leaf proteomic profiles, in order to elucidate molecular mechanisms involved in tolerance to Cd toxicity. Cacao scion-rootstock combinations were grown in soil with 150 mg Cd kg-1 soil, together with the control treatment. Leaf samples were collected 96 h after treatments were applied. There were alterations in the leaf proteome of the cacao scion-rootstock combinations, whose molecular responses to Cd toxicity varied depending on the combination. Leaf proteomic analyzes provided important information regarding the molecular mechanisms involved in the tolerance and intolerance of cacao scion-rootstock combinations to Cd toxicity. Enzymatic and non-enzymatic antioxidant systems, efficient for eliminating ROS, especially the expressions of APX and SOD, in addition to the increase in the abundance of metalloproteins, such as ferredoxins, rubredoxin, ALMT, Trx-1 and ABC-transporter were key mechanisms used in the Cd detoxification in cacao scion-rootstock combinations tolerant to Cd toxicity. Carboxylic acid metabolism, glucose activation and signal transduction were also important processes in the responses of cacao scion-rootstock combinations to Cd toxicity. The results confirmed CCN 51/BN 34 as a cacao scion-rootstock combination efficient in tolerance to Cd toxicity.

Clonal integration can promote the growth and spread of Alternanthera philoxeroides in cadmium-contaminated environments

Clonal plants are able to support the growth of their ramets in stressful environments via clonal integration between the ramets. However, it remains unclear whether the developmental status of stressed ramets affects the role of clonal integration. Here, we explored the effects of clonal integration at both the ramet level and the whole clonal fragment level when the apical ramets (younger) and basal ramets (older) were subjected to different concentrations of cadmium contamination. We grew pairs of ramets of Alternanthera philoxeroides, which were connected or disconnected by stolon between them. The apical and basal ramets were either uncontaminated or individually subjected to Cd contamination at concentrations of 5 mg kg-1 and 50 mg kg-1, respectively. Our results showed that clonal integration significantly promoted the growth of apical ramets subjected to Cd contamination. More importantly, under high Cd treatment, clonal integration also had a significant positive effect on the fitness of the whole clonal fragments. However, clonal integration did not affect plant growth when basal ramets were subjected to Cd contamination. Our study reveals the influence of the developmental status of stressed ramets on the role of clonal integration in heterogeneous heavy metal stress environments, suggesting that clonal integration may facilitate the spread of A. philoxeroides in Cd-contaminated habitats.

Mitigation strategies for excessive cadmium in rice

Cadmium (Cd)-contaminated rice is a human food safety problem that lacks a clear solution. A large amount of rice having an excessive Cd content is processed yearly, but it cannot be discarded and placed in landfills because it will cause secondary pollution. How do we best cope with this toxic rice? From the perspectives of food safety, food waste prevention, and human hunger eradication, the use of contemporary physical, chemical, and biological techniques to lower the Cd content in postharvest Cd-contaminated rice so that it can be used safely is the best course of action. In this review, the contamination, chemical speciation, and distribution of Cd in rice are analyzed and discussed, as are the methods of Cd removal from rice, including a comparison of the advantages and disadvantages of various techniques. Owing to the limitations of current technology, research and technological development recommendations for removing Cd from rice grain are presented. The chemical and biological methods produce higher Cd-removal rates than physical methods. However, they are limited to small-scale laboratory applications and cannot be applied on a large industrial scale. For the efficient safe removal of Cd from food, mixed fermentation with lactic acid bacteria and yeast has good application prospects. However, limited strains having high Cd-removal rates have been screened. In addition, modern biotechnology has rarely been applied to reduce rice Cd levels. Therefore, applying genetic engineering techniques to rapidly obtain microorganisms with high Cd-removal rates in rice should be the focus of future research.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

An integrated transcriptome, metabolomic, and physiological investigation uncovered the underlying tolerance mechanisms of Monochoria korsakowii in response to acute/chronic cadmium exposure

Identifying the physiological response and tolerance mechanism of wetland plants to heavy metal exposure can provide theoretical guidance for an early warning for acute metal pollution and metal-contaminated water phytoremediation. A hydroponic experiment was employed to investigate variations in the antioxidant enzyme activity, chlorophyll content, and photosynthesis in leaves of Monochoria korsakowii under 0.12 mM cadmium ion (Cd2+) acute (4 d) and chronic (21 d) exposure. Transcriptome and metabolome were analyzed to elucidate the underlying defensive strategies. The acute/chronic Cd2+ exposure decreased chlorophyll a and b contents, and disturbed photosynthesis in the leaves. The acute Cd2+ exposure increased catalase activity by 36.42%, while the chronic Cd2+ exposure markedly increased ascorbate peroxidase, superoxide dismutase, and glutathione peroxidase activities in the leaves. A total of 2 685 differentially expressed genes (DEGs) in the leaves were identified with the plants exposed to the acute/chronic Cd2+ contamination. In the acute Cd2+ exposure treatment, DEGs were preferentially enriched in the plant hormone transduction pathway, followed by phenylrpopanoid biosynthesis. However, the chronic Cd2+ exposure induced DEGs enriched in the biosynthesis of secondary metabolites pathway as priority. With acute/chronic Cd2+ exposure, a total of 157 and 227 differentially expressed metabolites were identified in the leaves. Conjoint transcriptome and metabolome analysis indicated the plant hormone signal transduction pathway and biosynthesis of secondary metabolites was preferentially activated by the acute and chronic Cd2+ exposure, respectively. The phenylpropanoid pathway functioned as a chemical defense, and the positive role of deoxyxylulose phosphate pathway in leaves against acute/chronic Cd2+ exposure was impaired.

Microplastics promoted cadmium accumulation in maize plants by improving active cadmium and amino acid synthesis

Combined pollution from microplastics (MPs) and cadmium (Cd) can influence soil environment and soil biota, altering plant growth and development, and Cd mobilization. We investigated the effects of polystyrene (PS) and polypropylene (PP) MPs alongside Cd on soil Cd bioavailability, rhizosphere soil metabolomics, bacterial community structure, and maize (Zea mays L.) growth in two soil types (red soil and cinnamon soil). Although the addition of PS/PP-Cd promoted Cd accumulation in maize plants overall, there were large-particle-size- and small-particle-size-dependent effects in the red soil and cinnamon soil, respectively. The difference is mainly due to the capacity of the large particle size MPs to significantly reduce soil pH, improve soil electrical conductivity (EC), promote active Cd, and intensify Cd mobilization in red soil. In contrast, small-size MPs in cinnamon soil promoted the synthesis and secretion of rhizosphere amino acids and soil metabolites, thus promoting Cd absorption by maize roots. Soil microorganisms also improved Cd bioavailability via C-related functional bacteria. Overall, our study provides novel insights on the potential effects of combined MPs and Cd pollution on soil ecology and agricultural production, enhancing our understanding of rhizosphere metabolites in different soils.

Phytoremediation as a potential technique for vehicle hazardous pollutants around highways

With the synchronous development of highway construction and the urban economy, automobiles have entered thousands of households as essential means of transportation. This paper reviews the latest research progress in using phytoremediation technology to remediate the environmental pollution caused by automobile exhaust in recent years, including the prospects for stereoscopic forestry. Currently, most automobiles on the global market are internal combustion vehicles using fossil energy sources as the primary fuel, such as gasoline, diesel, and liquid or compressed natural gas. The composition of vehicle exhaust is relatively complex. When it enters the atmosphere, it is prone to a series of chemical reactions to generate various secondary pollutants, which are very harmful to human beings, plants, animals, and the eco-environment. Despite improving the automobile fuel quality and installing exhaust gas purification devices, helping to reduce air pollution, the treatment costs of these approaches are expensive and cannot achieve zero emissions of automobile exhaust pollutants. The purification of vehicle exhaust by plants is a crucial way to remediate the environmental pollution caused by automobile exhaust and improve the environment along the highway by utilizing the ecosystem's self-regulating ability. Therefore, it has become a global trend to use phytoremediation technology to restore the automobile exhaust pollution. Now, there is no scientific report or systematic review about how plants absorb vehicle pollutants. The screening and configuration of suitable plant species is the most crucial aspect of successful phytoremediation. The mechanisms of plant adsorption, metabolism, and detoxification are reviewed in this paper to address the problem of automobile exhaust pollution.

Fluorescent-Dye-Labeled Amino Acids for Real-Time Imaging in Arabidopsis thaliana

Amino acid is the main transport form of reduced nitrogen in plants. To investigate the uptake and source–sink translocation process of plants to help understand their physiological roles and transport mechanisms, we designed and synthesized three fluorescent-dye-labeled amino acids as tools to visualize amino acid transportation in Arabidopsis thaliana; these amino acids consist of amino acids linked to the fluorophore nitrobenzoxadiazole (NBD) with excellent optical properties. Furthermore, we incubated Arabidopsis thaliana with these NBD fluorescent-dye-labeled amino acids for real-time imaging along with fluorescence enhancement for 24 h. The results showed that Arabidopsis thaliana could absorb them directly from the roots to the leaves. Therefore, our fluorescent-dye-labeled amino acids provide a de novo tool and strategy for visualizing amino acid absorption and transportation in plants.

Comparative proteome profiles of Polygonatum cyrtonema Hua rhizomes (Rhizoma Ploygonati) in response to different levels of cadmium stress

BACKGROUND

The Polygonatum cyrtonema Hua rhizomes (also known as Rhizoma Polygonati, RP) are consumed for their health benefits. The main source of the RP is wild P. cyrtonema populations in the Hunan province of China. However, the soil Cadmium (Cd) content in Huanan is increasing, thus increasing the risks of Cd accumulation in RP which may end up in the human food chain. To understand the mechanism of Cd accumulation and resistance in P. cyrtonema, we subjected P. cyrtonema plants to four levels of Cd stress [(D2) 1, (D3) 2, (D4) 4, and (D5) 8 mg/kg)] compared to (D1) 0.5 mg/kg.

RESULTS

The increase in soil Cd content up to 4 mg/kg resulted in a significant increase in tissue (root hair, rhizome, stem, and leaf) Cd content. The increase in Cd concentration variably affected the antioxidant enzyme activities. We could identify 14,171 and 12,115 protein groups and peptides, respectively. There were 193, 227, 260, and 163 differentially expressed proteins (DEPs) in D2, D3, D4, and D5, respectively, compared to D1. The number of downregulated DEPs increased with an increase in Cd content up to 4 mg/kg. These downregulated proteins belonged to sugar biosynthesis, amino acid biosynthesis-related pathways, and secondary metabolism-related pathways. Our results indicate that Cd stress increases ROS generation, against which, different ROS scavenging proteins are upregulated in P. cyrtonema. Moreover, Cd stress affected the expression of lipid transport and assembly, glycolysis/gluconeogenesis, sugar biosynthesis, and ATP generation.

CONCLUSION

These results suggest that an increase in soil Cd content may end up in Huangjing. Cadmium stress initiates expression changes in multiple pathways related to energy metabolism, sugar biosynthesis, and secondary metabolite biosynthesis. The proteins involved in these pathways are potential candidates for manipulation and development of Cd stress-tolerant genotypes.

Metabolic profiles in the xylem sap of Brassica juncea exposed to cadmium

Metabolic profiles in xylem sap are considered a fundamental mechanism for Cadmium (Cd) detoxification in plants. However, the metabolic mechanism of Brassica juncea xylem sap in response to Cd is still unclear. Here, we investigated the effects on the metabolomics of B. juncea xylem sap treated with Cd at different times by utilizing a nontargeted liquid chromatography-mass spectrometry (LC-MS)-based metabolomics method for further elucidating the response mechanism of Cd exposure. The findings indicated that 48 h and 7 days Cd exposure caused significant differences in metabolic profiles of the B. juncea xylem sap. Those differential metabolites are primarily involved in amino acids, organic acids, lipids, and carbohydrates, and most of them were downregulated, which played essential roles in response to Cd stress. Furthermore, B. juncea xylem sap resisted 48-h Cd exposure via regulation of glycerophospholipid metabolism, carbon metabolism, aminoacyl-tRNA biosynthesis, glyoxylate and dicarboxylate metabolism, linoleic acid metabolism, C5-branched dibasic acid metabolism, alpha-linolenic acid metabolism, cyanoamino acid metabolism, ABC transporters, biosynthesis of amino acids, and pyrimidine metabolism; whereas alpha-linolenic acid metabolism, glycerophospholipid metabolism, photosynthesis, and oxidative phosphorylation were regulated for resisting 7-day Cd exposure.

Microbially induced calcium precipitation coupled with medical stone-coated sponges: A targeted strategy for enhanced nitrate and fluoride removal from groundwater

The coexistence of nitrate and fluoride in groundwater is of high concern due to its potential environmental impacts and health risks. Medical stone-coated sponges, as a microbial activity promoter and slow-release calcium source, were introduced into an immobilized bioreactor for enhanced removal of nitrate and fluoride. Under the hydraulic retention time of 3 h, nitrate, fluoride, and calcium contents of 16.5, 3.0, and 100 mg L^-1, the average removal efficiencies of nitrate, fluoride, and calcium reached 99.49%, 74.26%, and 70.43%, respectively. Co-precipitation and chemisorption were the mechanisms for fluoride and calcium removal. Medical stone load improved the competitiveness of dominant bacteria and electron transport activity, accelerated the denitrification process, and stimulated biofilm formation. High fluoride level (5.0 mg L^-1) inhibited the nitrate removal and aromatic protein production. The fluoride content changes altered the carbon source preference of the microbial community, which preferred to use amino acids and carbohydrates under a higher fluoride content. The introduction of medical stones significantly accelerated the fluoride and nitrate removal, providing a new insight for the application of microbially induced calcium precipitation technique in the remediation of low-calcium groundwater.

Role of Root Exudates in Cadmium Accumulation of a Low-Cadmium-Accumulating Tobacco Line (Nicotiana tabacum L.)

Root exudates are tightly linked with cadmium (Cd) uptake by the root and thus affect plant Cd accumulation. A hydroponic experiment was carried out to explore the role of root exudates in Cd accumulation of a low-Cd-accumulating tobacco line (RG11) compared with a high-Cd- accumulating tobacco line (Yuyan5). Greater secretion of organic acids and amino acids by the roots was induced by an exogenous Cd addition in the two tobacco lines. The concentration of organic acid secreted by RG11 was only 51.1~61.0% of that secreted by Yuyan5. RG11 roots secreted more oxalic acid and acetic acid and less tartaric acid, formic acid, malic acid, lactic acid, and succinic acid than Yuyan5 under Cd stress. Oxalic acid accounted for 26.8~28.8% of the total organic acids, being the most common component among the detected organic acids, and was significantly negatively correlated with Cd accumulation in RG11. Propionic acid was only detected in the root exudates of RG11 under Cd stress. Lactic acid was positively linked with Cd accumulation in Yuyan5, being less accumulated in RG11. Similarly, RG11 secreted more amino acids than Yuyan5 under Cd stress. Aspartic acid, serine, and cysteine appeared in RG11 when it was exposed to Cd. Lysine was the most secreted amino acid in RG11 under Cd stress. RG11 roots secreted less lysine, histidine, and valine, but more phenylalanine and methionine than Yuyan5 under Cd stress. The results show that organic acids and amino acids in root exudates play a key role in Cd uptake by the root, and this contribution varied with cultivar/genotype. However, further research is still needed to explore the mechanisms underlying low Cd translocation to the leaf, which may be the key contribution of low Cd accumulation in RG11 to the security of tobacco leaf.

Integrated physiologic and proteomic analysis of Stropharia rugosoannulata mycelia in response to Cd stress

Soil Cd pollution seriously threatens environment and human health. Due to its ability to absorb and accumulate Cd in mycelia, Stropharia rugosoannulata could be a potential candidate for bioremediation of Cd-contaminated soils; however, the response mechanism of mycelia to Cd stress is still unclear. In this study, the physiologic and proteomic differences of S. rugosoannulata mycelia under 0.2 mg/L (low) and 2 mg/L (high) Cd stress were investigated. The results showed that Cd accumulation and mycelial growth inhibition exhibited a concentration-depended trend. Analysis of antioxidant system indicated that SOD, GR, GSH, GSSG and ASA played key roles in resisting the toxic effects of Cd. Via proteome analysis, 24 and 267 differentially expressed proteins (DEPs) were observed under low and high Cd stress, respectively. GO and KEGG analysis found that the mycelial growth inhibition might due to the down-regulation of some DEPs involved in "valine, leucine and isoleucine biosynthesis" and "tyrosine metabolism"; the certain tolerance to high Cd stress might attribute to the regulation of DEPs referred to energy metabolism and antioxidant system-related pathways, maintaining cellular energy homeostasis and removing ROS. These results provide a theoretical basis for further elucidation of response mechanisms in S. rugosoannulata to Cd stress.

Could nitrogen compounds be indicators of tolerance to high doses of Cu and Fe in the cultivation of Leucaena leucocephala?

Nitrogen metabolism and the production of primary and secondary metabolites vary according to biotic and abiotic factors such as trace elements (TE) stress, and can, therefore, be considered biomarkers. The present study evaluated the effect of copper (Cu) and iron (Fe) TE, separately, on the metabolism of nitrogen compounds and biomass production, partitioned into shoot and roots of Leucaena leucocephala (Lam.) de Wit., and identified possible defense mechanisms linked to nitrogen metabolism. At 120 days of cultivation, the biomass production of L. leucocephala was higher when exposed to excess Fe than Cu. Nonetheless, the biomass gain (%) of plants exposed to Cu was higher, especially the biomass gains in roots. The tolerance and biomass production of L. leucocephala is related to the regulation of nitrogen metabolism and production of secondary metabolites. The biochemistry of plant metabolism against the excess of Cu and Fe TE manifested similarly, but with some specifics regarding the chemical nature of each metal. There was a reduction in the content of ureides and proteins and an increase in amino acids in the roots in relation to the increase in Cu and Fe concentrations. There was low accumulation of proline in the roots in treatments 400 and 500 mg/dm³ compared to the control for both TE. On the other hand, the total phenolic compounds in the roots increased. Our results indicate that the increased synthesis of amino acids and the accumulation of phenolic compounds is involved in the tolerance of L. leucocephala to Cu and Fe.

Growth, physiological, and temperature characteristics in chinese cabbage pakchoi as affected by Cd- stressed conditions and identifying its main controlling factors using PLS model

BACKGROUND

Although hormesis induced by heavy metals is a well-known phenomenon, the involved biological mechanisms are not fully understood. Cadmium (Cd) is a prevalent heavy metal in the environment. Exposure of Cd, via intake or consumption of Cd-contaminated air or food, poses a huge threat to human health. Chinese cabbage pakchoi (Brassica chinensis L.) is widely planted and consumed as a popular vegetable in China. Therefore, studying the response of Chinese cabbage pakchoi to Cd- stressed conditions is critical to assess whether cabbage can accumulate Cd and serve as an important Cd exposure pathway to human beings. In this study, we investigated the influence of Cd stress on growth, photosynthetic physiology, antioxidant enzyme activities, nutritional quality, anatomical structure, and canopy temperature in Chinese cabbage pakchoi. A partial least squares (PLS) model was used to quantify the relationship between physical and chemical indicators with Cd accumulation in cabbage, and identify the main controlling factors.

RESULTS

Results showed that Cd stress significantly inhibited cabbage's growth and development. When Cd stress was increased, the phenotypic indicators were significantly reduced. Meanwhile, Cd stress significantly enhanced the oxidative stress response of cabbage, such as the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and the content of malondialdehyde (MDA) in leaves. Such a change tended to increase fenestrated tissues' thickness but decrease the thickness of leaf and spongy tissues. Moreover, Cd stress significantly increased soluble sugar, protein, and vitamin C contents in leaves as well as the temperature in the plant canopy. The PLS model analysis showed that the studied phenotypic and physicochemical indicators had good relationships with Cd accumulation in roots, shoots, and the whole plant of cabbage, with high coefficient of determination (R²) values of 0.891, 0.811, and 0.845, and low relative percent deviation (RPD) values of 3.052, 2.317, and 2.557, respectively. Furthermore, through analyzing each parameter's variable importance for projection (VIP) value, the SOD activity was identified as a key factor for indicating Cd accumulation in cabbage. Meanwhile, the effects of CAT on Cd accumulation in cabbage and the canopy mean temperature were also high.

CONCLUSION

Cd stress has significant inhibitory effects and can cause damage cabbage's growth and development, and the SOD activity may serve as a key factor to indicate Cd uptake and accumulation in cabbage.

A fungus (Trametes pubescens) resists cadmium toxicity by rewiring nitrogen metabolism and enhancing energy metabolism

As a primary goal, cadmium (Cd) is a heavy metal pollutant that is readily adsorbed and retained in rice, and it becomes a serious threat to food safety and human health. Fungi have attracted interest for their ability to remove heavy metals from the environment, although the underlying mechanisms of how fungi defend against Cd toxicity are still unclear. In this study, a Cd-resistant fungus Trametes pubescens (T. pubescens) was investigated. Pot experiments of rice seedlings colonized with T. pubescens showed that their coculture could significantly enhance rice seedling growth and reduce Cd accumulation in rice tissues. Furthermore, integrated transcriptomic and metabolomic analyses were used to explore how T. pubescens would reprogram its metabolic network against reactive oxygen species (ROS) caused by Cd toxicity. Based on multi-omic data mining results, we postulated that under Cd stress, T. pubescens was able to upregulate both the mitogen-activated protein kinase (MAPK) and phosphatidylinositol signaling pathways, which enhanced the nitrogen flow from amino acids metabolism through glutaminolysis to α-ketoglutarate (α-KG), one of the entering points of tricarboxylic acid (TCA) cycle within mitochondria; it thus increased the production of energy equivalents, adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) for T. pubescens to resist oxidative damage. This study can enable a better understanding of the metabolic rewiring of T. pubescens under Cd stress, and it can also provide a promising potential to prevent the rice paddy fields from Cd toxicity and enhance food safety.

Metabolic pathways reveal the effect of fungicide loaded metal-organic frameworks on the growth of wheat seedlings

Metal-organic frameworks (MOF) are an emerging class of hybrid inorganic-organic porous materials used in various fields, especially in molecule delivery system. As iron is an essential micronutrient for plant growth, iron-based MOF (Fe-MOF) is developed for agricultural application as fungicide carriers. However, fungicides may have various effect on the plant growth, which may be different from Fe-MOF. When they are combined with the carriers, the effects on target plants will change. In this work, tebuconazole-loaded Fe-MOF was prepared and used to treat wheat seedlings. The physiological, biochemical and metabolic levels of wheat roots and shoots were shown by a comparative study. Related metabolic pathways were analyzed by non-targeted metabolomic method. Many metabolites in wheat roots and shoots showed an upward trend after Fe-MOF treatment, but tebuconazole had a negative impact on these indicators. Related metabolic pathways in Fe-MOF and tebuconazole treatment were different, and the related pathway of tebuconazole-loaded Fe-MOF was closer to that of Fe-MOF. The metabolic pathways study revealed that the negative impact from tebuconazole was mitigated when wheat seedlings were treated with tebuconazole-loaded Fe-MOF. This research firstly explores the mechanism of MOF as carriers to help plant reduce the negative effects from fungicide by regulating metabolic pathways.

Proanthocyanidins Alleviate Cadmium Stress in Industrial Hemp (Cannabis sativa L.)

Industrial hemp (Cannabis sativa L.), an annual herbaceous cash crop, is widely used for the remediation of heavy metal-contaminated soils due to its short growth cycle, high tolerance, high biomass, and lack of susceptibility to transfer heavy metals into the human food chain. In this study, a significant increase in proanthocyanidins was found in Yunnan hemp no. 1 after cadmium stress. Proanthocyanidins are presumed to be a key secondary metabolite for cadmium stress mitigation. Therefore, to investigate the effect of proanthocyanidins on industrial hemp under cadmium stress, four experimental treatments were set up: normal environment, cadmium stress, proanthocyanidin treatment, and cadmium stress after pretreatment with proanthocyanidins. The phenotypes from the different treatments were compared. The experimental results showed that pretreatment with proanthocyanidins significantly alleviated cadmium toxicity in industrial hemp. The transcriptome and metabolome of industrial hemp were evaluated in the different treatments. Proanthocyanidin treatment and cadmium stress in industrial hemp mainly affected gene expression in metabolic pathways associated with glutathione metabolism, phenylpropanoids, and photosynthesis, which in turn altered the metabolite content in metabolic pathways of phenylalanine, vitamin metabolism, and carotenoid synthesis. The combined transcriptomic and metabolomic analysis revealed that proanthocyanidins mitigated cadmium toxicity by enhancing photosynthesis, secondary metabolite synthesis, and antioxidant synthesis. In addition, exogenous proanthocyanidins and cadmium ions acted simultaneously on EDS1 to induce the production of large amounts of salicylic acid in the plant. Finally, overexpression of CsANR and CsLAR, key genes for proanthocyanidins synthesis in industrial hemp, was established in Arabidopsis plants. The corresponding plants were subjected to cadmium stress, and the results showed that CsLAR transgenic plants were more tolerant to cadmium than the CsANR transgenic and wild-type Arabidopsis plants. The results showed that salicylic acid and jasmonic acid were increased in Arabidopsis overexpressing CsLAR compared to AT wild-type Arabidopsis, and levels of secondary metabolites were significantly higher in Arabidopsis overexpressing CsLAR than in AT wild-type Arabidopsis. These results revealed how proanthocyanidins alleviated cadmium stress and laid the foundation for breeding industrial hemp varieties with higher levels of proanthocyanidins and greater tolerance.

Physiological and rhizospheric response characteristics to cadmium of a newly identified cadmium accumulator Coreopsis grandiflora Hogg. (Asteraceae)

Screening for superior cadmium (Cd) phytoremediation resources and uncovering the mechanisms of plant response to Cd are important for effective phytoremediation of Cd-polluted soils. In this study, the characteristics of Coreopsis grandiflora related to Cd tolerance and accumulation were analyzed to evaluate its Cd phytoremediation potential. The results revealed that C. grandiflora can tolerate up to 20 mg kg^-1 of Cd in the soil. This species showed relatively high shoot bioconcentration factors (1.09-1.85) and translocation factors (0.46-0.97) when grown in soils spiked with 5-45 mg kg^-1 Cd, suggesting that C. grandiflora is a Cd accumulator and can potentially be used for Cd phytoextraction. Physiological analysis indicated that antioxidant enzymes (i.e., superoxide dismutase, peroxidase, and catalase) and various free amino acids (e.g., proline, histidine, and methionine) participate in Cd detoxification in C. grandiflora grown in soil spiked with 20 mg kg^-1 of Cd (Cd20). The overall microbial richness and diversity remained similar between the control (Cd0) and Cd20 soils. However, the abundance of multiple rhizospheric microbial taxa was altered in the Cd20 soil compared with that in the Cd0 soil. Interestingly, many plant growth-promoting microorganisms (e.g., Nocardioides, Flavisolibacter, Rhizobium, Achromobacter, and Penicillium) enriched in the Cd20 soil likely contributed to the growth and vitality of C. grandiflora under Cd stress. Among these, some microorganisms (e.g., Rhizobium, Achromobacter, and Penicillium) likely affected Cd uptake by C. grandiflora. These abundant plant growth-promoting microorganisms potentially interacted with soil pH and the concentrations of Cd and AK in soil. Notably, potassium-solubilizing microbes (e.g., Rhizobium and Penicillium) may effectively solubilize potassium to assist Cd uptake by C. grandiflora. This study provides a new plant resource for Cd phytoextraction and improves our understanding of rhizosphere-associated mechanisms of plant adaptation to Cd-contaminated soil.

Free amino acids, carbon and nitrogen isotopic compositions responses to cadmium stress in two castor (Ricinus communis L.) species

Cadmium (Cd) toxicity induce various disturbances in metabolic processes and impair plant establishment. The composition of carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) and free amino acids (FAAs) can reflect the response of plants to environmental stress. In the present study, a solution culture experiment was carried out, and the secretion characteristics of FAAs as well as δ¹³C and δ¹⁵N were evaluated as indicative of the functional performance of two castor species (Zibo-3 and Zibo-9) under various Cd concentrations stress (0, 1, 2, and 5 mg L^-1). The results indicated that: 1) The treatment of the plants with 5 mg L^-1 of a Cd solution resulted in a significant decline of biomasses by 22.4% and 11.6% in Zibo-3 and Zibo-9, respectively, relative to controls; additionally, the accumulation levels for Cd in Zibo-9 were higher than those in Zibo-3, thus Zibo-9 showed higher tolerance and enrichment ability to Cd. 2) The exposure of castor to Cd treatments results in significant modifications in individual FAAs, suggesting a differential sensitivity of each biosynthetic pathway to this stress; however, a positive correlation was found between the accumulation of total FAAs and Cd treatment dosages; higher proportion of asparagine and glutamate in total amino acids for Zibo-9, and abundant secretion of arginine in Cd treated Zibo-9 may be associated with the higher Cd-tolerance and Cd-accumulation in Zibo-9. 3) Cd stress increased leaf δ¹³C and δ¹⁵N values regardless of the castor species; δ¹³C and δ¹⁵N could be used as monitoring tools for heavy metal stress in plants.

Untargeted LC-MS/MS-Based Metabolomic Profiling for the Edible and Medicinal Plant Salvia miltiorrhiza Under Different Levels of Cadmium Stress

Salvia miltiorrhiza, a medicinal and edible plant, has been extensively applied to treat cardiovascular diseases and chronic hepatitis. Cadmium (Cd) affects the quality of S. miltiorrhiza, posing serious threats to human health. To reveal the metabolic mechanisms of S. miltiorrhiza's resistance to Cd stress, metabolite changes in S. miltiorrhiza roots treated with 0 (CK), 25 (T1), 50 (T2) and 100 (T3) mg kg-1 Cd by liquid chromatography coupled to mass spectrometry (LC-MS/MS) were investigated. A total of 305 metabolites were identified, and most of them were amino acids, organic acids and fatty acids, which contributed to the discrimination of CK from the Cd-treated groups. Among them, S. miltiorrhiza mainly upregulated o-tyrosine, chorismate and eudesmic acid in resistance to 25 mg kg-1 Cd; DL-tryptophan, L-aspartic acid, L-proline and chorismite in resistance to 50 mg kg-1 Cd; and L-proline, L-serine, L-histidine, eudesmic acid, and rosmarinic acid in resistance to 100 mg kg-1 Cd. It mainly downregulated unsaturated fatty acids (e.g., oleic acid, linoleic acid) in resistance to 25, 50, and 100 mg kg-1 Cd and upregulated saturated fatty acids (especially stearic acid) in resistance to 100 mg kg-1 Cd. Biosynthesis of unsaturated fatty acids, isoquinoline alkaloid, betalain, aminoacyl-tRNA, and tyrosine metabolism were the significantly enriched metabolic pathways and the most important pathways involved in the Cd resistance of S. miltiorrhiza. These data elucidated the crucial metabolic mechanisms involved in S. miltiorrhiza Cd resistance and the crucial metabolites that could be used to improve resistance to Cd stress in medicinal plant breeding.

Transcriptomics Integrated with Changes in Cell Wall Material of Chestnut (Castanea mollissima Blume) during Storage Provides a New Insight into the “Calcification” Process

Chestnut “calcification” is the result of a series of physiological and biochemical changes during postharvest storage; however, the associated mechanisms are unclear. In this study, several potential calcification-related physicochemical parameters in chestnut, including moisture, cell wall materials, cellulose, lignin, and pectin, were measured. Transcriptome analysis was performed on chestnut seeds during different stages of storage. The results showed that the degree of calcification in the chestnut seeds was significantly negatively correlated with the moisture content (r = −0.961) at room temperature (20–25 °C) and a relative humidity of 50–60%. The accumulation of cell wall material in completely calcified seeds was 5.3 times higher than that of fresh seeds. The total content of cellulose and lignin increased during the storage process. Transcriptome analysis of 0% and 50% calcified chestnut was performed; a total of 1801 differentially expressed genes consisting of 805 up-regulated and 996 down-regulated genes were identified during the calcification process. Furthermore, response to water, water deprivation, and salt stress were most enriched by gene ontology (GO) and gene set enrichment analysis (GSEA). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to chestnut calcification included purine metabolism, RNA degradation, the mRNA surveillance pathway, starch and sucrose metabolism, arginine and proline metabolism, and fatty acid metabolism, and were detected. Most of the genes involved in cellulose synthase, lignin catabolism, and pectin catabolism were down-regulated, while only two important genes, scaffold11300 and scaffold0412, were up-regulated, which were annotated as cellulose and pectin synthase genes, respectively. These two genes may contribute to the increase of total cell wall material accumulation during chestnut calcification. The results provided new insights into chestnut calcification process and laid a foundation for further chestnut preservation.

Effects of Soil Amendments on Soil Pb Bioavailability and Pb Absorption by a low-Pb Accumulator Kumquat Grown in Two Types of Pb-Contaminated Soils

A pot experiment was conducted to investigate the effects of 0.5% and 1% alkaline, clay mineral and phosphorus amendments, as well as 2% and 5% organic amendments, on lead (Pb) soil bioavailability and Pb absorption by the low-Pb accumulator kumquat (Citrus japonica Thunb.) 'Cuipi' in two typical Pb-contaminated soils, Jiyuan and Yangshuo, from northern and southern China, respectively. The diethylenetriaminepentaacetic acid-extractable Pb soil concentration and Pb accumulation in kumquat significantly decreased with amendment additions. High amendment doses had greater inhibitory effects than low doses but no significant effects on the kumquat's biomass in the two typical soils. Alkaline, but not clay mineral, amendments greatly increased the soil pH level. Organic amendments effectively reduced Pb accumulation owing to their strong adsorptive capacities. Thus, using organic amendments combined with a low-Pb accumulator kumquat forms a suitable farming practice for producing safe fruit in the two common types of Pb-contaminated soils in China.

Cd absorption characteristics of Suaeda salsa under different sediment burial and exogenous Cd input conditions in the Yellow River estuary, China

Suaeda salsa (L.) Pall., a typical halophyte plant in the Yellow River estuary, has high enrichment capacity for heavy metals. However, few studies have investigated the Cd absorption characteristics of S. salsa under different sediment burial and exogenous Cd input conditions, especially following the water-sediment regulation scheme (WSRS), which brought sediment burial and exogenous substances to the estuary. So, we established a greenhouse pot culture experiment with four sediment burial depths (0 cm, 3 cm, 6 cm, and 12 cm) and exogenous Cd input levels (0 mg·kg-1, 0.5 mg·kg-1, 1.0 mg·kg-1, and 1.5 mg·kg-1) and analyzed the leaf, stem, root, and total biomass; leaf, stem, and root Cd content; and storage, sediment Cd content, accumulation factor, root/leaf (R/L), root/stem (R/S), and stem/leaf (S/L) ratios to study the Cd absorption characteristics of S. salsa under the different sediment burial and exogenous Cd input. Results showed that high Cd content in roots, stems, and leaves was harmful to S. salsa growth, and then led to a decrease in biomass (characterized by stem, leaf, and total biomass). Suaeda salsa exhibited a survival strategy to deal with Cd toxicity, which involved the roots absorbing Cd from the sediment and storing it in stems and leaves (stem and leaf Cd content peaked at 0.5 mg·kg-1 Cd input) at low Cd input, whereas roots stored more Cd and reduced Cd transport to stems and leaves at high Cd input. Therefore, we observed the maximum value of leaf (500.63 ± 19.15 g·m-2), stem (648.22 ± 50.08 g·m-2), and total biomass (1246.92 ± 55.49 g·m-2) in the treatment with 1.5 mg·kg-1 Cd input and 3-cm sediment depth due to the Cd content in leaves and stems being relatively low. The accumulation factors of leaves, stems, and roots varied (0.39-0.99, 0.19-2.58, and 0.80-20.45, respectively), and most of the accumulation factors for roots and leaves and the R/L and R/S ratios were >1, which indicated that S. salsa had high enrichment levels of Cd, which mostly accumulated in the roots. Shallow or moderate burial depth was beneficial to S. salsa growth, but sediment burial was not beneficial to Cd absorption because the sum of leaf, stem, and root Cd storage was higher at 0-cm depth compared with the other depths. Variance analysis showed that the influence of Cd input on leaf, stem, root, and sediment Cd content and stem and root Cd storage was significant (P < 0.05), whereas sediment burial, interaction of sediment burial and Cd input on Cd content, storage, and biomass were not significant (P > 0.05). Therefore, we concluded that more attention should be paid to the control of sediment burial and heavy metal input, especially during the WSRS, in the Yellow River estuary.

The role of glutathione-mediated triacylglycerol synthesis in the response to ultra-high cadmium stress in Auxenochlorella protothecoides

Under ultra-high cadmium (Cd) stress, large amounts of glutathione are produced in Auxenochlorella protothecoides UTEX 2341, and the lipid content increases significantly. Glutathione is the best reductant that can effectively remove Cd, but the relationship between lipid accumulation and the cellular response to Cd stress has not been ascertained. Integrating analyses of the transcriptomes and lipidomes, the mechanism of lipid accumulation to Cd tolerance were studied from the perspectives of metabolism, transcriptional regulation and protein glutathionylation. Under Cd stress, basic metabolic pathways, such as purine metabolism, translation and pre-mRNA splicing process, were inhibited, while the lipid accumulation pathway was significantly activated. Further analysis revealed that the transcription factors (TFs) and genes related to lipid accumulation were also activated. Analysis of the TF interaction sites showed that ABI5, MYB_rel and NF-YB could further regulate the expression of diacylglycerol acyltransferase through glutathionylation/deglutathionylation, which led to increase of the triacylglycerol (TAG) content. Lipidomes analysis showed that TAG could help maintain lipid homeostasis by adjusting its saturation/unsaturation levels. This study for the first time indicated that glutathione could activate TAG synthesis in microalga A. protothecoides, leading to TAG accumulation and glutathione accumulation under Cd stress. Therefore, the accumulation of TAG and glutathione can confer resistance to high Cd stress. This study provided insights into a new operation mode of TAG accumulation under heavy metal stress.

Astaxanthin and its gold nanoparticles mitigate cadmium toxicity in rice by inhibiting cadmium translocation and uptake

Cadmium (Cd) is one of the main heavy metal in rice, Cd uptake by cereal crops from soil leads to toxicity in plants and pose serious health risks due to human body's accumulation through the food chain. Astaxanthin, a natural and anti-oxidative oxycarotenoid, is widely distributed in various microorganisms and seafood. In this study, we demonstrated that astaxanthin in the form of gold nanoparticles (Ast-AuNPs) can efficiently alleviate Cd toxicity to a greater extent in hydroponically grown rice plants than single astaxanthin. When supplemented with 100 μg/mL Ast-AuNPs in medium, the Cd level of rice was significantly reduced by 26.2% (in roots) and 85.9% (in leaves), respectively. We also found Ast-AuNPs supplement restores chlorophyll biosynthesis and mitigate Cd-induced oxidative stresses: the contents of superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) were significantly reduced while the activity of the antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) was significantly elevated. Further study showed that the supplement of Ast-AuNPs inhibited Cd-induced gene expression of the metal transporter genes (OsHMA2, OsHMA3, OsIRT1, OsIRT2, OsNramp1, and OsNramp5) in rice roots. Moreover, Ast-AuNPs regulated the metabolism of free amino acids and increased the level of non-enzymatic antioxidants such as glutathione and ascorbic acid. Therefore, this study demonstrates that Ast-AuNPs could mitigate the Cd toxicity in rice seedlings by suppressing Cd uptake, scavenging of ROS, and enhancing the activity of antioxidants, and also expands the application of functional gold nanoparticles in the alleviation of heavy metal pollution in plants.

Comprehensive Evaluation of Amino Acids and Polyphenols in 69 Varieties of Green Cabbage (Brassica oleracea L. var. capitata L.) Based on Multivariate Statistical Analysis

The biological activities of the primary metabolites and secondary metabolites of 69 green cabbage varieties were tested. The LC-MS detection method was used to determine the content of 19 free amino acids (lysine, tryptophan, phenylalanine, methionine, threonine, isoleucine, leucine, valine, arginine, asparagine, glycine, proline, tyrosine, glutamine, alanine, aspartic acid, serine, and glutamate). The content of 10 polyphenols (chlorogenic acid, gallic acid, 4-coumaric acid, ferulic acid, gentisic acid, cymarin, erucic acid, benzoic acid, rutin, and kaempferol) was determined by the HPLC detection method. Considering the complexity of the data obtained, variance analysis, diversity analysis, correlation analysis, hierarchical cluster analysis (HCA), and principal component analysis (PCA) were used to process and correlate amino acid or polyphenol data, respectively. The results showed that there were significant differences between the different amino acids and polyphenols of the 69 cabbage varieties. The most abundant amino acids and polyphenols were Glu and rutin, respectively. Both amino acids and polyphenols had a high genetic diversity, and multiple groups of significant or extremely significant correlations. The 69 cabbage varieties were divided into two groups, according to 19 amino acid indexes, by PCA. Among them, seven varieties with high amino acid content all fell into the fourth quadrant. The HCA of amino acids also supports this view. Based on 10 polyphenols, the 69 cabbage varieties were divided into two groups by HCA. Based on 29 indexes of amino acids and polyphenols, 69 cabbage varieties were evaluated and ranked by PCA. Therefore, in this study, cabbage varieties were classified in accordance with the level of amino acids and polyphenols, which provided a theoretical basis for the genetic improvement of nutritional quality in cabbage.

The mitochondrial pyruvate carrier (MPC) complex mediates one of three pyruvate-supplying pathways that sustain Arabidopsis respiratory metabolism

Malate oxidation by plant mitochondria enables the generation of both oxaloacetate and pyruvate for tricarboxylic acid (TCA) cycle function, potentially eliminating the need for pyruvate transport into mitochondria in plants. Here, we show that the absence of the mitochondrial pyruvate carrier 1 (MPC1) causes the co-commitment loss of its putative orthologs, MPC3/MPC4, and eliminates pyruvate transport into Arabidopsis thaliana mitochondria, proving it is essential for MPC complex function. While the loss of either MPC or mitochondrial pyruvate-generating NAD-malic enzyme (NAD-ME) did not cause vegetative phenotypes, the lack of both reduced plant growth and caused an increase in cellular pyruvate levels, indicating a block in respiratory metabolism, and elevated the levels of branched-chain amino acids at night, a sign of alterative substrate provision for respiration. 13C-pyruvate feeding of leaves lacking MPC showed metabolic homeostasis was largely maintained except for alanine and glutamate, indicating that transamination contributes to the restoration of the metabolic network to an operating equilibrium by delivering pyruvate independently of MPC into the matrix. Inhibition of alanine aminotransferases when MPC1 is absent resulted in extremely retarded phenotypes in Arabidopsis, suggesting all pyruvate-supplying enzymes work synergistically to support the TCA cycle for sustained plant growth.

Phosphate-solubilizing bacterium Burkholderia sp. strain N3 facilitates the regulation of gene expression and improves tomato seedling growth under cadmium stress

Cadmium (Cd) is among the most toxic heavy metals in soils. The ways by which tomato plants inoculated with a phosphate-solubilizing bacterium (PSB) respond to Cd and regulate gene expression remain unclear. We investigated hormone metabolism and genes involved in Cd resistance in tomato seedlings inoculated with the PSB strain N3. Cd inhibited tomato plant growth and nutrient uptake and increase in dry weight. Compared with Cd treatment, N3 inoculation inhibited the accumulation of Cd in the shoots and roots, and the root dry weight significantly increased by 30.50% (P < 0.05). The nitrogen and potassium contents in the roots of seedlings treated with N3 increased, and the phosphorus levels were the same as those in the control. N3 decreased the rate of Zn²⁺ absorption but increased Fe³⁺ absorption in the roots, and the amount of accumulated Cd increased with Zn²⁺ uptake. The concentrations of hormones (indole-3-acetic acid, IAA; zeatin, ZEA; and jasmonic acid, JA) increased under Cd stress, whereas inoculation with N3 reduced IAA and ZEA levels. In the comparison between N3 + Cd and Cd treatments, the highest number of up- and downregulated genes was obtained. Pathways involved in signaling response, photosynthesis, phenylpropanoid biosynthesis, and DNA replication and the photosynthesis-antenna proteins pathway play important roles in the responses and adaptation of seedlings to Cd. Inoculation with N3 alleviates Cd stress in tomato seedlings. The present study provides new insights into the differentially expressed genes related to interaction between PSB and tomato exposed to Cd in soils.

Metabolic Profiles of Brassica juncea Roots in Response to Cadmium Stress

Brassica juncea has great application potential in phytoremediation of cadmium (Cd)-contaminated soil because of its excellent Cd accumulating and high biomass. In this study, we compared the effects of Cd under 48 h and 7 d stress in roots of Brassica juncea using metabolite profiling. The results showed that many metabolic pathways and metabolites in Brassica juncea roots were altered significantly in response to Cd stress. We found that significant differences in levels of amino acids, organic acids, carbohydrates, lipids, flavonoids, alkaloids, and indoles were induced by Cd stress at different times, which played a pivotal role in the adaptation of Brassica juncea roots to Cd stress. Meanwhile, Brassica juncea roots could resist 48 h Cd stress by regulating the biosynthesis of amino acids, linoleic acid metabolism, aminoacyl-tRNA biosynthesis, glycerophospholipid metabolism, ABC transporters, arginine biosynthesis, valine, leucine and isoleucine biosynthesis, and alpha-linolenic acid metabolism; however, they regulated alpha-linolenic acid metabolism, glycerophospholipid metabolism, ABC transporters, and linoleic acid metabolism to resist 7 d Cd stress. A metabolomic expedition to the response of Brassica juncea to Cd stress will help to comprehend its tolerance and accumulation mechanisms of Cd.

The regulatory role of root in cadmium accumulation in a high cadmium-accumulating rice line (Oryza sativa L.)

There are some key processes that regulate cadmium (Cd) accumulation in rice. Understanding the characteristics and mechanisms of Cd accumulation in high Cd-accumulating rice lines benefits for excavating relevant genes. Cd accumulation and distribution in roots of Lu527-8, a high Cd-accumulating rice line, were investigated by a hydroponic experiment, with a control of a normal rice line (Lu527-4). Lu527-8 showed significantly higher Cd concentrations in roots than Lu527-4. More than 81% of Cd in roots of two rice lines is distributed in soluble fraction and cell wall. In soluble fraction, there were more organic acids, amino acids, and phytochelatins in Lu527-8, benefiting Cd accumulation. Pectin and hemicellulose 1 (HC1), especially pectin, were main polysaccharides in cell wall. Lu527-8 showed more pectin and HC1 along with higher pectin methylesterase (PME) activity compared with Lu527-4, promoting Cd accumulation. Besides, Lu527-8 showed higher Cd translocation from root to shoot due to more amounts of ethanol-extractable Cd in roots than Lu527-4. In conclusion, specific characteristics of Cd chemical forms and subcellular distribution in roots of high Cd-accumulating rice line are important for Cd accumulation and translocation.

A novel role of sulfate in promoting Mn phytoextraction efficiency and alleviating Mn stress in Polygonum lapathifolium Linn

A hydroponic method was performed to explore the effects of sulfate supply on the growth, manganese (Mn) accumulation efficiency and Mn stress alleviation mechanisms of Polygonum lapathifolium Linn. Three Mn concentrations (1, 8 and 16 mmol L^-1, representing low (Mn1), medium (Mn8) and high (Mn16) concentrations, respectively) were used. Three sulfate (S) levels (0, 200, and 400 μmol L^-1, abbreviated as S0, S200 and S400, respectively) were applied for each Mn concentration. (1) The average biomass (g plant^-1) of P. lapathifolium was ordered as Mn8 (6.36) > Mn1 (5.25) > Mn16 (4.16). Under Mn16 treatment, S addition increased (P < 0.05) biomass by 29.96% (S200) and 53.07% (S400) compared to that S0. The changes in the net photosynthetic rate and mean daily increase in biomass were generally consistent with the changes in biomass. (2) Mn accumulation efficiency (g plant^-1) was ordered as Mn8 (99.66) > Mn16 (58.33) > Mn1 (27.38); and S addition increased (p < 0.05) plant Mn accumulation and Mn transport, especially under Mn16 treatment. (3) In general, antioxidant enzyme activities (AEAs) and malondialdehyde (MDA) in plant leaves were ordered in Mn16 > Mn8 > Mn1. Sulfate addition decreased (P < 0.05) AEAs and MDA under Mn16 treatment, while the changes were minor under Mn1 and Mn8 treatments. (4) Amino acid concentrations generally increased with increasing Mn concentration and S level. In summary, the medium Mn treatment promoted plant growth and Mn bioaccumulation; sulfate, especially at 400 µmol L^-1 S, can effectively promote plant growth and Mn accumulation efficiency. The most suitable bioremediation strategy was Mn16 with 400 µmol L^-1 S.

Floristic surveys of some lowlands polluted of a tropical urban area: the case of Yaounde, Cameroon

This study presents original results for field surveys in lowland sites polluted in Yaounde-Cameroon. The screening of 11 polluted lowlands compared to a natural lowland (unpolluted), made it possible to identify species which may exhibit the best capacities to adapt to environmental changes and to develop in contaminated areas, in particular heavy metals. This work can be a preliminary study around the species growing in contaminated lowlands. Thus, this study can be reproduced in other regions, to compare the results obtained and identify potential plants for the lowlands remediation in Cameroon.

Protective role of l-threonine against cadmium toxicity in Saccharomyces cerevisiae

Environment and food contamination with cadmium (Cd) can cause serious toxicity, posing a severe threat to agricultural production and human health. However, how amino acids contribute to defenses against oxidative stress caused by Cd in cells is not fully understood. As a model eukaryote with a relatively clear genetic background, Saccharomyces cerevisiae has been commonly used in Cd toxicity research. To gain insight into Cd toxicity and cell defenses against it, 20 amino acids were screened for protective roles against Cd stress in S. cerevisiae. The results showed that threonine (Thr, T) had the strongest protective effect against Cd-induced mortality and membrane damage in the cells. Compared to the antioxidant vitamin C (VC), Thr exhibited a higher efficacy in restoring the superoxide dismutase (SOD) activity that was inhibited by Cd but not by H₂ O₂ in vivo. Thr exhibited evident DPPH (2,2-diphenyl-1-picrylhydrazyl) activity but weak ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-9 sulfonic acid)) scavenging activity, giving it a weaker effect against Cd-induced lipid peroxidation and superoxide radical O^2- , compared to VC. More importantly, compared to the chelating agent EDTA, Thr showed stronger chelation of Cd, giving it a stronger protective effect on SOD against Cd than VC in vitro. The results of the in vivo and in vitro experiments revealed that the role Thr plays in cell defenses against Cd may be attributed to its protection of the SOD enzyme, predominantly through the preferential chelation of Cd. Our results provide insights into the protective mechanisms of amino acid Thr that ameliorate Cd toxicity and suggest that a supplement of Thr might help to reduce Cd-induced oxidative damage.

Phytoremediation potential of Youngia japonica (L.) DC: a newly discovered cadmium hyperaccumulator

Cadmium (Cd) is one of the most toxic contaminants, causing a lot of harm to environment and the human health. An outdoor pot experiment for 60 days was conducted to study the Cd(II) effects on growth, biomass, physiological properties, Cd uptake, and accumulation in Youngia japonica plants but also to evaluate the effect of Y. japonica growth on enzyme activity of Cd-contamination soils. Generally, the application of Cd(II) less than 120 mg kg^-1 stimulated the growth of the plants, whereas at 160 mg kg^-1 or higher levels, a significant reduction was observed. For all treatments > 10 mg kg^-1 Cd(II) in soil, values of Cd in roots and aboveground parts were more than the critical value of 100 mg kg^-1 and reached highest values of 252.51 and 314.29 mg kg^-1, respectively. The bioconcentration factors (BCF) and translation factors (TF) for all Cd treatments were more than 1.0, with the former ranging from 1.03 to 5.46 and the later from 1.04 to 1.33. The activities of peroxidase (POD) and superoxide dismutase (SOD), as well as the levels of glutathione (GSH) and proline in Y. japonica plants after exposure to 10-200 mg kg^-1 Cd(II) were stimulated, implying that they were defensive guards to the oxidative stress produced by Cd. The urease, dehydrogenase, and alkaline phosphatase activities under low Cd concentrations can be enhanced by planting Y. japonica species but inhibited under high Cd concentrations. Our data provide comprehensive evidence that Y. japonica has the typical properties of a Cd hyperaccumulator and thus may be practically employed to alleviate Cd from contaminated soils.