Cadmium accumulation capacity and resistance strategies of a cadmium-hypertolerant fern - Microsorum fortunei

Exploration the interaction of cadmium and copper toxic effects in pakchoi (Brassica chinensis L) roots through combinatorial transcriptomic and weighted gene co-expression network analysis

The interaction between cadmium(Cd) and copper(Cu) during combined pollution can lead to more complex toxic effects on humans and plants.However, there is still a lack of sufficient understanding regarding the types of interactions at the plant molecular level and the response strategies of plants to combined pollution. To assess this, we investigated the phenotypic and transcriptomic patterns of pakchoi (Brassica chinensis L) roots in response to individual and combined pollution of Cd and Cu. The results showed that compared to single addition, the translocation factor of heavy metals in roots significantly decreased (p < 0.05) under the combined addition, resulting in higher accumulation of Cd and Cu in the roots. Transcriptomic analysis of pakchoi roots revealed that compared to single pollution, there were 312 and 1926 differentially expressed genes (DEGs) specifically regulated in the Cd2Cu20 and Cd2Cu100 combined treatments, respectively. By comparing the expression of these DEGs among different treatments, we found that the combined pollution of Cd and Cu mainly affected the transcriptome of the roots in an antagonistic manner. Enrichment analysis indicated that pakchoi roots upregulated the expression of genes involved in glucosetransferase activity, phospholipid homeostasis, proton transport, and the biosynthesis of phenylpropanoids and flavonoids to resist Cd and Cu combined pollution. Using weighted gene co-expression network analysis (WGCNA), we identified hub genes related to the accumulation of Cd and Cu in the roots, which mainly belonged to the LBD, thaumatin-like protein, ERF, MYB, WRKY, and TCP transcription factor families. This may reflect a transcription factor-driven trade-off strategy between heavy metal accumulation and growth in pakchoi roots. Additionally, compared to single metal pollution, the expression of genes related to Nramp, cation/H+ antiporters, and some belonging to the ABC transporter family in the pakchoi roots was significantly upregulated under combined pollution. This could lead to increased accumulation of Cd and Cu in the roots. These findings provide new insights into the interactions and toxic mechanisms of multiple metal combined pollution at the molecular level in plants.

Impacts of simulated atmospheric cadmium deposition on the physiological response and cadmium accumulation of Sedum plumbizincicola

Atmospheric cadmium (Cd) deposition contributes to the accumulation of Cd in the soil-plant system. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. However, studies on the effects of atmospheric Cd deposition on the accumulation of Cd and physiological response in S. plumbizincicola are still limited. A Cd solution spraying pot experiment was conducted with S. plumbizincicola at three atmospheric Cd deposition concentrations (4, 8, and 12 mg/L). Each Cd concentration levels was divided into two groups, non-mulching (foliar-root uptake) and mulching (foliar uptake). The soil type used in the experiment was reddish clayey soil collected from a farmland. The results showed that compared with the non-mulching control, the fresh weight of S. plumbizincicola in non-mulching with high atmospheric Cd deposition (12 mg/L) increased by 11.35%. Compared with those in the control group, the malondialdehyde (MDA) content in the non-mulching and mulching S. plumbizincicola groups increased by 0.88-11.06 nmol/L and 0.96-1.32 nmol/L, respectively. Compared with those in the non-Cd-treated control group, the shoot Cd content in the mulching group significantly increased by 11.09-180.51 mg/kg. Under high Cd depositions, the Cd in S. plumbizincicola mainly originated from the air and was stored in the shoots (39.7-158.5%). These findings highlight that the physiological response and Cd accumulation of S. plumbizincicola were mainly affected by high Cd deposition and suggest that atmospheric Cd could directly be absorbed by S. plumbizincicola. The effect of atmospheric deposition on S. plumbizincicola cannot be ignored.

Hydrogen sulfide alleviates chromium toxicity by promoting chromium sequestration and re-establishing redox homeostasis in Zea mays L

Hydrogen sulfide (H₂S) is a multifunctional gaseous signaling molecule involved in the regulation of Cr stress responses. In the present study, we combined transcriptomic and physiological analyses to elucidate the mechanism underlying the mitigation of Cr toxicity by H₂S in maize (Zea mays L.). We showed that treatment with sodium hydrosulfide (NaHS, a donor of H₂S) partially alleviated Cr-induced growth inhibition. However, Cr uptake was not affected. RNA sequencing suggested that H₂S regulates the expression of many genes involved in pectin biosynthesis, glutathione metabolism, and redox homeostasis. Under Cr stress, NaHS treatment significantly increased pectin content and pectin methylesterase activity; thus, more Cr was retained in the cell wall. NaHS application also increased the content of glutathione and phytochelatin, which chelate Cr and transport it into vacuoles for sequestration. Furthermore, NaHS treatment mitigated Cr-induced oxidative stress by enhancing the capacity of enzymatic and non-enzymatic antioxidants. Overall, our results strongly support that H₂S alleviates Cr toxicity in maize by promoting Cr sequestration and re-establishing redox homeostasis rather than by reducing Cr uptake from the environment.

Clean-Up of Heavy Metals from Contaminated Soil by Phytoremediation: A Multidisciplinary and Eco-Friendly Approach

Pollution from heavy metals is one of the significant environmental concerns facing the world today. Human activities, such as mining, farming, and manufacturing plant operations, can allow them access to the environment. Heavy metals polluting soil can harm crops, change the food chain, and endanger human health. Thus, the overarching goal for humans and the environment should be the avoidance of soil contamination by heavy metals. Heavy metals persistently present in the soil can be absorbed by plant tissues, enter the biosphere, and accumulate in the trophic levels of the food chain. The removal of heavy metals from contaminated soil can be accomplished using various physical, synthetic, and natural remediation techniques (both in situ and ex situ). The most controllable (affordable and eco-friendly) method among these is phytoremediation. The removal of heavy metal defilements can be accomplished using phytoremediation techniques, including phytoextraction, phytovolatilization, phytostabilization, and phytofiltration. The bioavailability of heavy metals in soil and the biomass of plants are the two main factors affecting how effectively phytoremediation works. The focus in phytoremediation and phytomining is on new metal hyperaccumulators with high efficiency. Subsequently, this study comprehensively examines different frameworks and biotechnological techniques available for eliminating heavy metals according to environmental guidelines, underscoring the difficulties and limitations of phytoremediation and its potential application in the clean-up of other harmful pollutants. Additionally, we share in-depth experience of safe removing the plants used in phytoremediation-a factor frequently overlooked when choosing plants to remove heavy metals in contaminated conditions.

Physiological, anatomical, and transcriptional responses of mulberry (Morus alba L.) to Cd stress in contaminated soil

Mulberry has been widely studied for its capacity to tolerate heavy metals. However, the anatomical and molecular response mechanisms of Cd detoxification and transportation in mulberry have not been fully elucidated. In this study, the anatomical characteristics, Cd and mineral element uptake and transport, and transcriptome profiling of mulberry were studied under Cd stress. The results showed that mulberry possessed strong detoxification and self-protection abilities against Cd stress. The growth and photosynthetic pigment contents of mulberry were only slightly affected when the soil Cd content was less than 37.0 mg/kg, while the Ca and Mg contents in the mulberry roots were clearly (p < 0.05) increased by 37.85%-40.87% and 36.63%-53.06% in 37.0-55.4 mg/kg Cd-contaminated soil. Meanwhile, the relationships between antioxidant enzyme activities, such as peroxidase, catalase, and ascorbate peroxidase, and Cd content in plants were positive. Furthermore, the structures of leaf cells, root and stem tissues were largely intact; simultaneously, the increase in osmiophilic particles and the dissolution of starch granules in mulberry leaves significantly responded to Cd stress. Clusters of Orthologous Groups of proteins (COG) and Gene Ontology (GO) classification analysis indicated that mulberry can enhance the catalytic activity, regulate the transport and metabolism of inorganic ions, and strengthen its antioxidant enzyme activity and defense mechanism to decrease Cd intoxication. Large numbers of differentially expressed genes associated with cell wall biosynthesis, antioxidant enzyme activities, glutathione metabolism, chelation, plant hormone signal transduction, and the mitogen-activated protein kinase (MAPK) signaling pathway were upregulated under Cd stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that plant hormone signal transduction was significantly (p < 0.05) enriched in roots, stems, and leaves of mulberry, and abscisic acid and ethylene can mediate MAPK signaling pathways to increase plant tolerance to Cd stress. The results suggested that the physiological, cellular and tissue, and transcriptional regulation of mulberry can facilitate its stress adaptation in Cd-contaminated soil.

De Novo Transcriptome Assembly of Two Microsorum Fern Species Identifies Enzymes Required for Two Upstream Pathways of Phytoecdysteroids

Microsorum species produce a high amount of phytoecdysteroids (PEs), which are widely used in traditional medicine in the Pacific islands. The PEs in two different Microsorum species, M. punctatum (MP) and M. scolopendria (MS), were examined using high-performance liquid chromatography (HPLC). In particular, MS produces a high amount of 20-hydroxyecdysone, which is the main active compound in PEs. To identify genes for PE biosynthesis, we generated reference transcriptomes from sterile frond tissues using the NovaSeq 6000 system. De novo transcriptome assembly after deleting contaminants resulted in 57,252 and 54,618 clean transcripts for MP and MS, respectively. The clean Microsorum transcripts for each species were annotated according to gene ontology terms, UniProt pathways, and the clusters of the orthologous group protein database using the MEGAN6 and Sma3s programs. In total, 1852 and 1980 transcription factors were identified for MP and MS, respectively. We obtained transcripts encoding for 38 and 32 enzymes for MP and MS, respectively, potentially involved in mevalonate and sterol biosynthetic pathways, which produce precursors for PE biosynthesis. Phylogenetic analyses revealed many redundant and unique enzymes between the two species. Overall, this study provides two Microsorum reference transcriptomes that might be useful for further studies regarding PE biosynthesis in Microsorum species.

Responses of glutathione and phytochelatins biosysthesis in a cadmium accumulator of Perilla frutescens (L.) Britt. under cadmium contaminated conditions

Screening new accumulators of heavy metal and identifying their tolerance, enrichment capacity of heavy metals are currently hot issues in phytoremediation research. A series of hydroponic experiments were conducted to analyze the effects of glutathione and phytochelatins in roots, stems, and leaves of Perilla frutescens under cadmium stress. The results showed that the non-protein thiols in roots and stems mainly existed in the form of GSH, PC₂, PC₃, and PC₄ under Cd stress condition, while in leaves they existed in the form of GSH, PC₂, and PC₃. Furthermore, the contents of GSH and PCs positively correlated with Cd, but negatively correlated with root vigor and chlorophyll content under Cd stress conditions. After 21 days of treatments, the contents of Cd in different parts of the plant were 1465.2-3092.9 mg· kg^-1 in the roots, 199.6-478.4 mg·kg^-1 in the stems and 61.3-96.9 mg· kg^-1 in the leaves at 2, 5, 10 mg·L^-1 Cd levels respectively, and the amount of Cd uptakes were up to 3547.7-5701.7 μg·plant^-1. Therefore, P. frutescens performed high capacity in Cd accumulation, and PCs played a key role in Cd tolerance. The application prospect of the plant in phytoremediation Cd polluted soil was also discussed.

Parental exposure to cadmium chloride causes developmental toxicity and thyroid endocrine disruption in zebrafish offspring

Cadmium is a common heavy metal pollutant. Previous studies have found that long-term cadmium exposure can cause damage to multiple organs/systems in humans and experimental animals; however, there are few studies that elucidate its effects on offspring development, discuss whether it can be transmitted to offspring from the parent, and debate whether it affects the functional development of the thyroid hormone system in offsprings. In this study, sexually mature zebrafish were exposed to different concentrations of cadmium chloride (0.01 μmol/L, 0.1 μmol/L, and 1 μmol/L) to study reproductive toxicity. It was found that parental zebrafish exposed to 1 μmol/L of cadmium chloride produced offsprings with different degrees of malformation. At 5 days post-fertilization (dpf), the levels of 3,5,3'-triiododenosine (T3) and thyroxine (T4) in the zebrafish were decreased. At 10 dpf, the T4 and T3 levels in the zebrafish of the offspring were significantly reduced. At the same time, the expression of thyroid receptor (trα and trβ) genes in five dpf larvae was significantly up-regulated in the 1 μmol/L treatment group relative to the control group. The mRNAs of thyroid hormone synthesis and metabolism-related genes (tshβ, dio1, dio2, ugt1ab, and ttr) were significantly up-regulated in the 0.1 μmol/L and 1 μmol/L treatment groups. This study demonstrates that parental cadmium chloride exposure produces reproductive toxicity in zebrafish and that the effects can be transferred from the parent to the offspring, resulting in developmental toxicity in the thyroid endocrine system.

Hyperaccumulation of Cd by Rorippa globosa (Turcz.) Thell. from soil enriched with different Cd compounds, and impact of soil amendment with glutathione (GSH) on the hyperaccumulation efficiency

Rorippa globosa (Turcz.) Thell. is known as Cd hyperaccumulator, however neither hyperaccumulation nature, nor affecting factors like the effect of Cd compounds entering soil from different sources, or of specific soil amendments, are not yet satisfactorily clarified. In the pot culture experiment, Cd accumulation by R. globosa from soils spiked with 3 and 9 mg Cd kg^-1 in the form of Cd(NO₃)₂, CdCl₂, CdBr₂, CdI₂, CdSO₄, CdF₂, Cd(OH)₂, CdCO₃, Cd₃(PO₄)₂, CdS and effect of soil amendment with glutathione (GSH) were investigated. Accumulation capacity of R. globosa for Cd appeared to reflect its extractability in soils and was about two-fold bigger for high soluble compounds than for low-soluble ones. At that, the differences between the accumulation of Cd originating from high soluble compound group did not exceed 20%, while the differences within the low soluble compound group were insignificant (p < 0.05). The analysis of Cd uptake, uptake factor (UF), enrichment factor (EF) and translocation factor (TF) patterns revealed that Cd hyperaccumulating properties of R. globosa are based on the high water/nutrients demand and strong tolerance to Cd, although weak protection against Cd uptake by root system was also observed. Amendment with GSH enhanced Cd availability to plant and its uptake from soil, but exerted no effect on Cd translocation in plants. In the light of the results, the use of R. globosa for phytoremediation of moderately polluted agricultural lands as forecrop or aftercrop, and the GSH-assisted phytoremediation of highly polluted post-industrial sites seem to be viable options.