Cd Accumulation Capacity Research Articles

Integrative physiological, transcriptomic, and metabolomic analysis of Abelmoschus manihot in response to Cd toxicity.

Rapid industrialization and urbanization have caused severe soil contamination with cadmium (Cd) necessitating effective remediation strategies. Phytoremediation is a widely adopted technology for remediating Cd-contaminated soil. Previous studies have shown that Abelmoschus manihot has a high Cd accumulation capacity and tolerance indicating its potential for Cd soil remediation. However, the mechanisms underlying its response to Cd stress remain unclear. In this study, physiological, transcriptomic, and metabolomic analyses were conducted to explore the response of A. manihot roots to Cd stress at different time points. The results revealed that Cd stress significantly increased malondialdehyde (MDA) levels in A. manihot, which simultaneously activated its antioxidant defense system, enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) by 19.73%-50%, 22.87%-38.89%, and 32.31%-45.40% at 12h, 36h, 72h, and 7 days, respectively, compared with those in the control (CK). Moreover, transcriptomic and metabolomic analyses revealed 245, 5,708, 9,834, and 2,323 differentially expressed genes (DEGs), along with 66, 62, 156, and 90 differentially expressed metabolites (DEMs) at 12h, 36h, 72h, and 7 days, respectively. Through weighted gene coexpression network analysis (WGCNA) of physiological indicators and transcript expression, eight hub genes involved in phenylpropanoid biosynthesis, signal transduction, and metal transport were identified. In addition, integrative analyses of metabolomic and transcriptomic data highlighted the activation of lipid metabolism and phenylpropanoid biosynthesis pathways under Cd stress suggesting that these pathways play crucial roles in the detoxification process and in enhancing Cd tolerance in A. manihot. This comprehensive study provides detailed insights into the response mechanisms of A. manihot to Cd toxicity.

Genome-wide identification of bHLH gene family and its response to cadmium stress in Populus × canescens.

The basic helix-loop-helix (bHLH) gene family is integral to various aspects of plant development and the orchestration of stress response. This study focuses on the bHLH genes within Populus × canescens, a poplar species noted for its significant tolerance to cadmium (Cd) stress. Through our comprehensive genomic analysis, we have identified and characterized 170 bHLH genes within the P. canescens genome. These genes have been systematically classified into 22 distant subfamilies based on their evolutionary relationships. A notable conservation in gene structure and motif compositions were conserved across these subfamilies. Further analysis of the promoter regions of these genes revealed an abundance of essential cis-acting element, which are associated with plant hormonal regulation, development processes, and stress response pathway. Utilizing quantitative PCR (qPCR), we have documented the differential regulation of PcbHLHs in response to elevated Cd concentrations, with distinct expression patterns observed across various tissues. This study is poised to unravel the molecular mechanism underpinning Cd tolerance in P. canescens, offering valuable insights for the development of new cultivars with enhanced Cd accumulation capacity and tolerance. Such advancements are crucial for implementing effective phytoremediation strategies to mitigate soil pollution caused by Cd.

CRISPR-mediated BnaNRAMP1 homologous copies editing create a low Cd-accumulation oilseed rape germplasm with unaffected yield

Brassica napus, one of the most important oil crops cultivated globally, is severely impacted by prolonged soil contamination with cadmium (Cd), resulting in decreased yields and poor seed quality. This crop exhibits a high adsorption capacity for Cd, thereby making the creation of seed resources with low Cd-accumulation as an essential strategy to alleviate this challenge. To address this issue, we genetically edited BnaNRAMP1 in B. napus by targeting three different exon regions, resulting in new germplasm resources with significant differences in Cd accumulation capacity and unaffected yield. Among these, the mutant K140-22, specifically targeting the seventh exon, is distinguished by its substantially reduced Cd accumulation. Further, enzyme assays of the antioxidant defense system in both roots and shoots of K140-22 revealed its enhanced antioxidant activity, which contributes to elucidate the molecular mechanisms of plant tolerance to heavy metal stress. Remarkably, this mutant also maintained equivalent agronomic traits and seed quality, which highlights its potential as a germplasm resource for rapeseed breeding for low Cd accumulation, as well as for elevating rapeseed economic value in Cd contaminated soil.

Comparative transcriptome combined with physiological analyses revealed key genes and pathways for cadmium tolerance in wild-type and mutant microalgae Dunaliella salina

Cadmium (Cd) has become one of the major contaminants in aquatic ecosystems. The microalgae Dunaliella salina is known as a cadmium (Cd) accumulator and shows a high level of tolerance to Cd, but improved Cd tolerance and relevant mechanisms are still required for investigation. In this study, two mutant strains (M1 and M2) of D. salina with high Cd resistance were obtained by chemical mutagenesis. In the normal medium, there were no differences between the two mutant strains and the wild-type strain in biochemical and physiological indicators. However, the two mutant strains showed high Cd resistance, rapid growth rate, and good Cd accumulation capacity in the medium containing high levels of Cd compared with the wild strain, which may be involved in increases in protein content, accumulation of carotenoids and chlorophylls, and glutathione reductase (GR) activity. We identified 829, 587, and 740 differentially expressed genes (DEGs) from the Cd/Control, Cd + M1/Cd, and Cd + M2/Cd sample groups by transcriptome analysis, respectively. The main DEGs were found in the ribosome, DNA replication, photosynthesis-antenna, and photosynthesis pathways after KEGG enrichment. There were 39 DEGs involved in the photosynthesis and photosynthesis-antenna pathways, of which 28 DEGs were down-regulated by Cd in the wild-type strain but remained relatively unchanged in the mutant strains. Under Cd exposure, the mutant strains showed higher mRNA levels of most DEGs involved in the ribosome and DNA replication pathways than the wild strain. Taken together, the present study will help us understand the mechanism of Cd tolerance in microalgae, and provide candidate genes and key pathways for phytoremediation.

Soil Cd increased the leaf litter Cd remains of Solanum nigrum and Solanum lycopersicum

Plant litter decomposition is a natural pathway of heavy metal cycling in soil ecosystems, but the dynamics of heavy metal release during litter decomposition are relatively poorly understood. The purpose of this study was to investigate the effects of species, soil fauna and soil Cd addition on litter decomposition and Cd release dynamics. Therefore, we selected two plants, Solanum nigrum and S. lycopersicum with large differences in Cd accumulation capacity. First, they were enriched with Cd during the growing period and leaf litter was harvested after 6 months of pretreatment. Then, the decomposition of leaf litter was conducted with or without soil Cd and Eisenia fetida through lab pot tests. Our results showed that leaf litter Cd led to a significant decrease in litter decomposition rate (K value), with a maximum decrease of 32.1% in S. nigrum and 30.1% in S. lycopersicum. We observed that the presence of E. fetida significantly increased K value, but the effect was similar in the +leaf Cd treatment and the -leaf Cd treatment, both for S. nigrum and S. lycopersicum. Interestingly, the litter Cd concentration did not decrease during decomposition, but showed an increasing trend, especially for S. nigrum in the +soil Cd treatment. Moreover, the litter Cd remains was higher in the +soil Cd treatment compared to the -soil Cd treatment for both S. nigrum and S. lycopersicum, no matter whether with or without E. fetida. This result suggests that the Cd may be transferred from soil to litter, thus increasing the litter Cd remains. Overall, our study shows that leaf litter Cd slowed down the carbon cycling in ecosystems. In addition, the release of litter Cd has a lag, and the litter has a certain adsorption capacity for soil Cd, which intensifies the harm to the ecology during litter transfer.

Accumulation and Release of Cadmium Ions in the Lichen Evernia prunastri (L.) Ach. and Wood-Derived Biochar: Implication for the Use of Biochar for Environmental Biomonitoring.

Biochar (BC) boasts diverse environmental applications. However, its potential for environmental biomonitoring has, surprisingly, remained largely unexplored. This study presents a preliminary analysis of BC's potential as a biomonitor for the environmental availability of ionic Cd, utilizing the lichen Evernia prunastri (L.) Ach. as a reference organism. For this purpose, the lichen E. prunastri and two types of wood-derived biochar, biochar 1 (BC1) and biochar 2 (BC2), obtained from two anonymous producers, were investigated for their ability to accumulate, or sequester and subsequently release, Cd when exposed to Cd-depleted conditions. Samples of lichen and biochar (fractions between 2 and 4 mm) were soaked for 1 h in a solution containing deionized water (control), 10 µM, and 100 µM Cd2+ (accumulation phase). Then, 50% of the treated samples were soaked for 24 h in deionized water (depuration phase). The lichen showed a very good ability to adsorb ionic Cd, higher than the two biochar samples (more than 46.5%), and a weak ability to release the metal (ca. 6%). As compared to the lichen, BC2 showed a lower capacity for Cd accumulation (-48%) and release (ca. 3%). BC1, on the other hand, showed a slightly higher Cd accumulation capacity than BC2 (+3.6%), but a release capacity similar to that of the lichen (ca. 5%). The surface area and the cation exchange capacity of the organism and the tested materials seem to play a key role in their ability to accumulate and sequester Cd, respectively. This study suggests the potential use of BC as a (bio)monitor for the presence of PTEs in atmospheric depositions and, perhaps, water bodies.

Tomato Accumulates Cadmium to a Concentration Independent of Plant Growth

Cadmium (Cd) contamination is a growing concern, as exposure to the metal has been shown to inhibit plant growth and development. However, soil Cd pollution in China is typically mild, and thus its concentration often does not impede plant growth. On the other hand, it is unknown if increased plant growth impacts Cd uptake, movement, and accumulation. Here, we analyzed the relationship between Cd accumulation in 31 tomato cultivars and the impact on specific growth parameters in mild Cd contamination. The results showed that there are variations in the Cd distribution among the 31 tomato cultivars studied. There were higher Cd concentrations in shoots of the cultivar ‘SV3557’, whereas root Cd concentrations were the lowest. The roots of the cultivar ‘HF11’ recorded the lowest Cd content but had higher Cd content in the shoots. The Cd concentration in roots and shoots was not related to root length, plant height, and root weight. However, Cd accumulation in the shoots was markedly promoted by root length and plant height, and Cd accumulation in the roots was promoted by root weight. Subsequently, we imposed Cd on four selected tomato cultivars to ascertain their accumulation in the shoot tissues. The results revealed that, among the four tomato cultivars, Cd was highly accumulated in the leaves, followed by the stems, and the fruits (leaf > stem > fruit). When identifying significant loci associated with Cd accumulation in tomato plants, it is crucial to find a suitable indicator to assess the plant’s ability to accumulate Cd. Thus, Cd concentration in shoots can be used as a reliable proxy for evaluating tomato plants’ capacity for Cd accumulation. This study serves as a valuable reference in guiding the selection of such an index.

Rhizospheric Lactobacillus spp. contribute to the high Cd-accumulating characteristics of Phytolacca spp. in acidic Cd-contaminated soil

Screening high Cd-accumulating plants and understanding the interactions between plants, rhizospheric microbes and Cd are important in developing microbe-assisted phytoremediation techniques for Cd-contaminated soils. In this study, the Cd tolerance and accumulation characteristics of Phytolacca americana L., P. icosandra L. and P. polyandra Batalin growing in acidic Cd-contaminated soil were compared to evaluate their phytoremediation potential. According to Cd concentrations (root: 8.26–37.09 mg kg−1, shoot: 2.80–9.26 mg kg−1), bioconcentration factors (BCFs) and translocation factors (TFs), the three Phytolacca species exhibited high Cd-accumulation capacities, ranked in the following order: P. icosandra (root BCF: 1.25, shoot BCF: 0.31, TF: 0.25) > P. polyandra (root BCF: 0.68, shoot BCF: 0.26, TF: 0.44) > P. americana (root BCF: 0.28, shoot BCF: 0.09, TF: 0.38). Phytolacca icosandra and P. polyandra can thus be considered as two new Cd accumulators for phytoremediation. Soil pH, available Cd (ACd) concentration and certain bacterial taxa (e.g. Lactobacillus, Helicobacter, Alistipes, Desulfovibrio and Mucispirillum) were differentially altered in the rhizospheres of the three Phytolacca species in comparison to unplanted soil. Correlation analysis showed that there were significant interactions between rhizospheric ACd concentration, pH and Lactobacillus bacteria (L. murinus, L. gasseri and L. reuteri), which affected Cd uptake by Phytolacca plants. The mono- and co-inoculation of L. murinus strain D51883, L. gasseri strain D51533 and L. reuteri strain D24591 in the rhizosphere of P. icosandra altered the rhizospheric pH and ACd concentrations, in addition to increasing the shoot Cd contents by 31.9%–44.6%. These results suggest that recruitment of rhizospheric Lactobacillus spp. by Phytolacca plants contributes to their high Cd-accumulating characteristics. This study provides novel insights into understanding the interactions between plants, rhizobacteria and heavy metals.

Cadmium up Taking and Allocation in Wood Species Associated to Cacao Agroforestry Systems and Its Potential Role for Phytoextraction.

Trees in cacao Agroforestry systems (AFS) may present a high potential for cadmium (Cd) phytoextraction, helping to reduce Cd in cacao (Theobroma cacao L.) plants grown in contaminated soils. To assess this potential, four forest fine-woody species commonly found in cacao high-productive sites in Colombia (Tabebuia rosea, Terminalia superba, Albizia guachapele, and Cariniana pyriformis) were exposed to contrasting CdCl2 contamination levels (0, 6, and 12 ppm) on a hydroponic medium. Growth dynamics, tolerance index (TI), and Cd concentration and allocation in leaves, stems, and roots were evaluated for up to 90 days after initial exposure. T. superba, A. guachapele, and C. pyriformis were classified as moderately tolerant (TI > 0.6), and T. rosea was considered a sensitive species (TI < 0.35) under 12 ppm Cd contamination. Despite showing a high stem Cd concentration, C. pyriformis also showed the lowest relative growth rate. Among the evaluated forest species, A. guachapele exhibited the highest Cd accumulation capacity per plant (2.02 mg plant-1) but also exhibited a higher Cd allocation to leaves (4%) and a strong decrease in leaf and stem dry mass after 90 days of exposure (~75% and 50% respectively, compared to control treatments). Taking together all the favorable features exhibited by T. superba as compared to other CAFS tree species and recognized phytoextractor tree species in the literature, such as Cd hyperaccumulation, high tolerance index, low Cd concentration in leaves, and high Cd allocation to the stem (harvestable as wood), this species is considered to have a high potential for cadmium phytoextraction in cocoa agroforestry systems.

Remediation Effect and Mechanism of Biochar in Combination with Nitrogen Fertilizer on Cd-contaminated Paddy Soil

Cadmium (Cd) heavy metal pollution has posed serious threats to soil health and the safe production utilization of agricultural products. A pot experiment was conducted to study the effects of biochar (BC) and nitrogen fertilizer with three levels, namely 2.6 g·pot-1 (N1), 3.5 g·pot-1 (N2), 4.4 g·pot-1 (N3) biochar combined with nitrogen fertilizer (BCN1, BCN2, and BCN3), on soil Cd fractions, Cd enrichment, the transport of rice, and soil enzyme activity, as well as the changes in microbial community composition and complex interactions between microorganisms through high-throughput sequencing. The results showed that biochar combined with nitrogen fertilizer led to the transformation of Cd from the exchangeable state to the residue state, and the proportion of the exchangeable state was significantly reduced by 6.2%-14.7%; by contrast, the proportion of the residue state increased by 18.6%-26.4% relative to that in CK. In addition, singular treatments of nitrogen fertilizer enhanced the accumulation capacities of Cd in roots, which increased by 22%-33.5% compared with that in CK. By contrast, the BC and BCN treatments reduced Cd accumulation in roots and the transfer capacity from stems to rice husks and husk to rice. Furthermore, the BCN treatments promoted soil enzyme activities (urease, acid phosphatase, invertase, and catalase). MiSeq sequencing showed that BCN treatments increased the abundance of the main species of soil bacterial microbes (such as Acidobacteriales, Solibacterales, Pedosphaerales, and Nitrospirales). Moreover, co-occurrence network analysis showed that the complexity of the soil bacterial network was enhanced under the N, BC, and BCN treatments. Overall, biochar combined with nitrogen fertilizer reduced soil Cd availability, inhibited the capacity of Cd accumulation and the transport of rice, and improved the soil eco-environmental quality. Thus, using BCN could be a feasible practice for the remediation of Cd-polluted agricultural soil.

Profound impact of water management on cadmium and arsenic accumulation in ratoon rice

Context or problemThere is limited information on the accumulation of cadmium (Cd) and arsenic (As) in grains of ratoon rice and how to regulate them through water management. Objective or research questionThis study aimed to determine the accumulation and transfer characteristics of Cd and As in main crop (MC) and ratoon crop (RC) under different water management practices, and to clarify the potential risk of Cd and As accumulation in the grains of MC and RC and related mechanisms. MethodsA two-year field experiment with two soil drying treatments (light drying and heavy drying, LD and HD) in the main season and two water treatments (flooded and rainfed) in the ratoon season was conducted in central China. Plants were sampled at the maturity of MC and RC, and the Cd and As concentrations in each organ were determined. ResultsIn the main season of 2019, compared with LD, HD significantly increased grain Cd concentration by 9.2 times, but decreased grain As concentration by 22.1%. However, frequent rainfall in the main season of 2018 weakened the difference between soil drying treatments. Across years in the ratoon season, rainfed treatment significantly increased grain Cd concentration by 9.3 times, while decreased grain As concentration by 30.2%, in comparison with flooded irrigation. RC exhibited a higher Cd pollution risk in grain than MC (23.2–388.7 vs 8.2–152.5 µg kg−1), which was attributed to the difference in Cd accumulation capacity in shoot. However, grain As concentration of RC was lower than that of MC regardless of water treatments (87.2–158.2 vs 152.2–261.6 µg kg−1). The low accumulation in shoot and transfer factor from shoot to grain of As were responsible for the low grain As concentration of RC. ConclusionsConsidering the climate conditions and the Cd and As accumulation capacity of MC and RC, it was recommended to heavily dry the soil in the main season and keep flooded in the ratoon season to produce safe rice with low grain Cd and As concentrations in ratoon rice. Implications and significanceThis study first clarified the accumulation and transfer characteristics of Cd and As in both seasons of ratoon rice, and provided recommendation of irrigation practices for meeting the national food safety standard of grain Cd and As concentrations for both seasons in the ratoon rice of central China.

Exogenous plant growth regulator and foliar fertilizers for phytoextraction of cadmium with Boehmeria nivea [L.] Gaudich from contaminated field soil

As a enrichment plant, ramie can be used for the phytoremediation of cadmium (Cd)-contaminated soil. However, it is worth exploring the role of plant growth regulators and foliar fertilizers in the process of plant growth and development and Cd adsorption. By measuring the agronomic traits, Cd content of aboveground and underground ramie, calculating the Cd transfer coefficient (TF) and Cd bioconcentration factors (BCF), and the correlation between various indicators. This study examined the effects of plant growth regulators and foliar fertilizers on ramie’s capacity for Cd accumulation and transportation. Plant growth regulators and foliar fertilizers increased the Cd content of the aboveground ramie, reduced the Cd content of the underground ramie, and increased the TF. Among them, GA-1 increased the Cd content of the aboveground ramie to 3 times more than that of the control and reduced the Cd content of the underground ramie by 54.76%. Salicylic acid (SA) increased the Cd content of the aboveground ramie to three times more than that of the control. The combination of GA and foliar fertilizer reduced the Cd content of the aboveground and underground ramie and the TF and BCF of the underground ramie. After the hormones were sprayed, the TF of ramie had a significant positive correlation with the Cd content of the aboveground ramie; the BCF of the aboveground ramie had a significant positive correlation with the Cd content and TF of the aboveground ramie. The results indicate that Brassinolide (BR), gibberellin (GA), ethephon (ETH), polyamines (PAs), and salicylic acid (SA) have different effects on the enrichment and transport of Cd in ramie. This study provided an effective method to improve the capacity for ramie to adsorb heavy metals during cultivation.

Field-scale differences in rhizosphere micro-characteristics of Cichorium intybus, Ixeris polycephala, sunflower, and Sedum alfredii in the phytoremediation of Cd-contaminated soil

Understanding the intricate interplay between Cd accumulation in plants and their rhizosphere micro-characteristics is important for the selection of plant species with profitable Cd phytoextraction and soil remediation efficiencies. This study investigated the differences in rhizosphere micro-ecological characteristics and Cd accumulation in chicory, Ixeris polycephala, sunflower, and Sedum alfredii in low-moderate Cd-contaminated soil. Data reveal that the dominant organic acids in rhizosphere soil that responded to Cd were oxalic and lactic acids in chicory and Ixeris polycephala, tartaric acid in sunflower, and succinic acid in Sedum alfredii. These unique organic acids could also influence the abundance of specific rhizobacterial communities in rhizosphere soil that were Sphingomonadaceae and Bradyrhizobiaceae in both Sedum alfredii (9.75 % and 2.56 %, respectively) and chicory (8.98 % and 2.82 %, respectively) rhizosphere soil, Xanthomonadaceae in both Sedum alfredii and Ixeris polycephala rhizosphere soil, and Gaiellaceae in chicory rhizosphere soil. In this case, the combined effects of the organic acids and unique rhizobacterial communities by plant species increased the bioavailable concentration of Cd in Sedum alfredii, Ixeris polycephala, and sunflower rhizosphere soil, while decreasing the Cd-DOM concentrations in chicory rhizosphere soil and the water-extractable Cd reduced by 88.02 % compared to the control. Though the capacity for Cd accumulation in the shoots of chicory was weaker than of Sedum alfredii but better than either Ixeris polycephala or sunflower, chicory presented better Cd translocation and harbored Cd mainly as the low toxic chemical form of pectates and proteins-bound Cd and Cd oxalate in its shoot. Generally, chicory, as an economic plant, is suitable for phytoremediation of low-moderate Cd-contaminated soil after Sedum alfredii.

Uptake and translocation of lead and cadmium in wild-found plant species from Bekasi and Karawang, West Java, for phytoremediation

Environmental degradation due to lead (Pb) and cadmium (Cd) pollution has been increasing. One of the alternative cost-effective green technologies to clean up heavy metal contamination is phytoremediation. This research aims to determine the potential of wild-found plants that could be used as Pb and Cd bioaccumulators. Plant species in this study were collected from heavy metal-contaminated soil in Bekasi and Karawang, West Java. Five species, namely Saccharum spontaneum, Acorus calamus, Ipomoea fistulosa, Ludwigia hyssopifolia, and Eichhornia crassipes, were studied for Pb accumulation capacity. Furthermore, five plant species, namely Limnocharis flava, Colocasia esculenta, Ipomoea fistulosa, Commelina benghalensis, and Eichhornia crassipes, were studied for their Cd accumulation capacity. The experiment was done in a greenhouse for eight weeks. Pb and Cd concentration were analyzed using atomic absorption spectrometry (AAS) to determine the uptake and translocation of Pb or Cd. I. fistulosa accumulated the highest amount of Pb, with a growth rate of up to 27.07 g week−1, a bioconcentration factor (BCF) of 1.46, and a translocation factor (TF) of 0.87 upon 300 mg kg−1 Pb treatment. C. esculenta showed considerable Cd bioaccumulation, as indicated by a BCF of 0.95 and a TF of 0.65, accompanied by sustained relative biomass increase (124.9%) and the highest growth rate (36.96 g week−1) among tested plant species upon 75 mg kg−1 Cd treatment. With their capacities for bioaccumulating Pb and Cd, respectively, I. fistulosa and C. esculenta were identified as potential accumulator species for phytoremediation in heavy metal-contaminated sites such as former mining lands, landfills, and highly polluted agricultural lands.

Assessment of the capability of cadmium accumulation and translocation among 31 willows: four patterns of willow biomass variation response to cadmium.

Cadmium (Cd) pollution threatens food security and the environment. Willow species (Salix, Salicaceae) exhibit a remarkable potential to restore Cd-polluted sites due to their high biomass production and high Cd accumulation capacities. This study examined the Cd accumulation and tolerance in 31 genotypes of shrub willow in hydroponic conditions at varying Cd levels (0μM Cd, 5μM Cd, and 20μM Cd). The root, stem, and leaf biomass of 31 shrub willow genotypes showed significant differences to Cd exposure. Among 31 willow genotypes, four patterns of biomass variation response to Cd were identified: insensitive to Cd; growth inhibition due to excessive Cd supply (high Cd inhibition); low Cd causing inhibited growth, whereas high Cd leading to increased biomass (U-shape); and growth increment with excessive Cd exposure (high Cd induction). The genotypes belonging to the "insensitive to Cd" and/or "high Cd induction" were candidates for the utilization of phytoremediation. Based on the analysis of Cd accumulation of 31 shrub willow genotypes at high and low Cd levels, genotypes 2372, 51-3, and 1052 obtained from a cross between S. albertii and S. argyracea grew well and accumulated relatively more Cd levels than other genotypes. In addition, for Cd-treated seedlings, root Cd accumulation was positively correlated with shoot Cd accumulation and total Cd uptake, demonstrating that Cd accumulation in roots could serve as a biomarker for evaluating the Cd extraction capacity of willows, especially in hydroponics screening. The results of this study screened out willow genotypes with high Cd uptake and translocation capacities, which will provide valuable approaches for restoring Cd-contaminated soils with willows.

Overexpression of LSU1 and LSU2 confers cadmium tolerance by manipulating sulfur metabolism in Arabidopsis

Phytoremediation using plants is an environmentally friendly and cost-effective strategy for removing cadmium (Cd) from soil. Plants used for phytoremediation must have a high Cd accumulation capacity and strong Cd tolerance. Therefore, understanding the molecular mechanism of Cd tolerance and accumulation in plants is of great interest. In response to Cd exposure, plants produce various thio-rich compounds, such as glutathione, phytochelatins, and metallothioneins, which play important roles in Cd immobilization, sequestration, and detoxification. Therefore, sulfur (S) metabolism is crucial for Cd tolerance and accumulation. In this study, we report that the overexpression of low-S responsive genes, LSU1 and LSU2, confers Cd tolerance in Arabidopsis. First, LSU1 and LSU2 promoted S assimilation under Cd stress. Second, LSU1 and LSU2 inhibited the biosynthesis and promoted the degradation of aliphatic glucosinolates, which could limit the consumption and enhance the release of S, thus, facilitating the production of the S-rich metabolites, glutathione, phytochelatins, and metallothioneins. We further demonstrated that the Cd tolerance mediated by LSU1 and LSU2 was dependent on the myrosinases BGLU28 and BGLU30, which catalyze the degradation of aliphatic glucosinolates. In addition, the overexpression of LSU1 and LSU2 improved Cd accumulation, which has great potential for the phytoremediation of Cd-contaminated soil.

DNA barcoding of marine macroalgae as bioindicators of heavy metal pollution

Metal pollution in the marine coastal environment is an important topical issue. In this study, the water quality in five locations along the Alexandria coast (Eastern Harbor, El-Tabia pumping station, El Mex Bay, Sidi Bishir, and Abu Talat) was assessed by measuring physicochemical parameters from water samples. Depending on the morphological classification of macroalgae, the collected morphotypes were related to Ulva fasciata, Ulva compressa, Corallina officinalis, Corallina elongata, and Petrocladia capillaceae. Corallina officinalis and Corallina elongata demonstrated a high capacity for Cd, Pb, and Ni accumulation, and the highest values of Fe, Cu, and Mn were reported in Ulva fasciata and Ulva compressa. Two standard markers were applied, and results showed that the morphological classification matched the molecular data. Moreover, the analysis of algae can only reflect the accumulation of metals. The conclusion is that Ulva compressa and Corallina officinalis are potentially suitable indicators of localized short-term heavy metal pollution.

Accumulation and Chemical Forms of Cadmium in Tissues of Different Vegetable Crops

Large areas of arable lands in China have been contaminated by heavy metals, in which cadmium (Cd) contamination was the most prevalent. Cd accumulation in main food crops and leafy vegetables grown in Cd-contaminated fields has aroused considerable attention in recent years. The present study investigated the Cd pollution of farmland soils and vegetables in Qujing city of Yunnan Province, China. By comparing the Cd uptake capacities of different crops, this study aimed to provide guidance for agricultural production in Cd-contaminated farmland, and clarify the influence of Cd bioavailability in soil and chemical forms of Cd in plant roots on its migration. Results showed that soil Cd concentration was up to 37 mg kg−1, which was 61-fold higher than the soil environmental quality standard in China. Concentration of Cd in 73% of the investigated vegetable samples, with the mean value of 5.43 mg Cd kg−1 (dry weight basis), exceeded the food safety standard of China. Leafy vegetables had the highest bioaccumulation factors (BF) and transfer factors (TF), with the mean values of 0.53 and 0.41, respectively. Water spinach (Ipomoea aquatica Forsk.), cole (Brassica campestris L.), and fennel (Foeniculum dulce Mill.) had the highest Cd TFs, with averages of 0.67, 0.66, and 0.64, respectively. On the contrary, garlic (Allium sativum L.), onions (Allium fistulosum L.), and pea (Lathyrus odoratus L.) had the lowest Cd TFs, with averages of 0.04, 0.03, and 0.04, respectively. The main chemical fraction of Cd in garlic root was insoluble phosphate (35–48%), whereas in water spinach root, it was pectate, protein binding or sorbed fraction (50–64%), resulting in a higher TF value of water spinach than garlic. These results indicate that there were significant differences in Cd uptake and accumulation between vegetables, and the Cd accumulation in leafy vegetable was significantly higher than that in alliums. Therefore, it is possible to reduce the uptake and accumulation of Cd in crop edible parts by the selection of vegetable species with low Cd accumulation capacity. The chemical fractions of Cd in crop roots, especially the proportions of more mobile fractions, might be an important reason for the root-to-shoot Cd transport and Cd accumulation in the aerial portions.

Metagenomic and machine learning-aided identification of biomarkers driving distinctive Cd accumulation features in the root-associated microbiome of two rice cultivars

Developing low-cadmium (Cd) rice cultivars has emerged as a promising avenue for food safety in Cd-contaminated farmlands. The root-associated microbiomes of rice have been shown to enhance rice growth and alleviate Cd stress. However, the microbial taxon-specific Cd resistance mechanisms underlying different Cd accumulation characteristics between different rice cultivars remain largely unknown. This study compared low-Cd cultivar XS14 and hybrid rice cultivar YY17 for Cd accumulation with five soil amendments. The results showed that XS14 was characterized by more variable community structures and stable co-occurrence networks in the soil-root continuum compared to YY17. The stronger stochastic processes in assembly of the XS14 (~25%) rhizosphere community than that of YY17 (~12%) suggested XS14 may have higher resistance to changes in soil properties. Microbial co-occurrence networks and machine learning models jointly identified keystone indicator microbiota, such as Desulfobacteria in XS14 and Nitrospiraceae in YY17. Meanwhile, genes involved in sulfur cycling and nitrogen cycling were observed among the root-associated microbiome of these two cultivars, respectively. Microbiomes in the rhizosphere and root of XS14 showed a higher diversity in functioning, with the significant enrichment of functional genes related to amino acid and carbohydrate transport and metabolism, and sulfur cycling. Our findings revealed differences and similarities in the microbial communities associated with two rice cultivars, as well as bacterial biomarkers predictive of Cd-accumulation capacity. Thus, we provide new insights into taxon-specific recruitment strategies of two rice cultivars under Cd stress and highlight the utility of biomarkers in offering clues for enhancing crop resilience to Cd stresses in the future.

Cadmium accumulation responses in Hylotelephium spectabile: The role of photosynthetic characteristics under different nitrogen, moisture, and light conditions

The influence of environmental factors on Cd accumulation by Hylotelephium spectabile and its physiological mechanisms are unclear. A field trial was conducted to investigate the effects of nitrogen, soil moisture, and light regulation on plant growth, Cd absorption and translocation, and the photosynthetic characteristics of two H. spectabile populations (LN with high Cd accumulation capacity and HB1 with relatively low Cd accumulation capacity). The results showed that Cd accumulation in LN was 59.6% higher than that in HB1 which may partly be explained by the inherent high transpiration rate of LN, especially at the terminal stage. In addition, the photosynthetic rate of LN responded more positively to nitrogen than HB1, which further amplified its advantages on plant growth and Cd accumulation. Moderate drought significantly stimulated root growth of LN, indicating that LN possesses stronger resistance to drought. Shade inhibited Cd distribution, rather than directly affecting Cd concentrations in H. spectabile. The combined stress of shade and drought had a synergistic effect on Cd translocation in H. spectabile. Moreover, LN achieved 17.3%∼444.5% higher transpiration levels than HB1 under environmental stress, which ensured a more efficient Cd transport capacity of LN. Therefore, the investigation of photosynthetic characteristics further revealed the physiological mechanism by which LN accumulated Cd superior to HB1 under environmental stress and responded more positively to nitrogen nutrition.