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Lead is an extensive contaminant. Pb-resistant bacterial strains were isolated from Saint Clair River sediments on two enrichment media with increasing concentrations of Pb (NO3)2. Bacterial strains that grew at 1.25 or 1.5 g L−1 of Pb (NO3)2 L−1) were purified and selected for further study. Ninety-seven Pb-resistant strains were screened for the ability to produce bioflocculants. The majority of the Pb-resistant strains demonstrated moderate to high flocculation activity. Metal removal assays demonstrated that the higher is the flocculation activity, the higher is the efficiency of metal removal. In the multi-metal solutions, the bacterial strain with the highest flocculation activity (R19) had the highest metal removing capability (six out of eight metals) and the highest metal removal efficiency. The highly selective affinity towards Pb2+ observed for strain R19 suggests its use for the recovery of Pb2+ from multiple metal solutions. Because they are well adapted to unfavorable conditions due to their resistance to metals (e.g., Pb) and antibiotics, these characteristics may help in developing an effective process for wastewater treatment using these strains.

Background Lead (Pb) pollution in soil has become one of the major environmental threats to plant growth and human health. Safe utilization of Pb contaminated soil by phytoremediation require Pb-tolerant rapeseed ( Brassica napus L.) accessions. However, breeding of new B. napus cultivars tolerance to Pb stress has been restricted by limited knowledge on molecular mechanisms involved in Pb tolerance. This work was carried out to identify genetic loci related to Pb tolerance during seedling establishment in rapeseed. Results Pb tolerance, which was assessed by quantifying radicle length (RL) under 0 or 100 mg/L Pb stress condition, shown an extensive variation in 472 worldwide-collected rapeseed accessions. Based on the criterion of relative RL > 80%, six Pb-tolerant genotypes were selected. Four quantitative trait loci (QTLs) associated with Pb tolerance were identified by Genome-wide association study. The expression level of nine promising candidate genes, including GSTUs , BCATs , UBP13 , TBR and HIPP01 , located in these four QTL regions, were significantly higher or induced by Pb in Pb-tolerant accessions in comparison to Pb-sensitive accessions. Conclusion To our knowledge, this is the first study on Pb-tolerant germplasms and genomic loci in B. napus . The findings can provide valuable genetic resources for the breeding of Pb-tolerant B. napus cultivars and understanding of Pb tolerance mechanism in Brassica species.

Heavy metal stress negatively affects the growth of medicinal plants. While the effects of Helium–Neon (He–Ne) laser on seed germination and stress tolerance in plants has garnered significant attention, little is known concerning the impacts of He–Ne laser irradiation on heavy metal tolerance in plants. Therefore, the current study was conducted to appraise the effect of different durations (0, 20, and 40 min) of seed priming with He–Ne laser (10 mW mm −2 ) on the antioxidant system of Silybum marianum L. plants under various Pb concentrations (0, 250, and 500 ppm). Lead phytotoxicity was evident by significant reductions in fresh and dry weights of shoots and roots, total chlorophyll (TChl) content and relative water content (RWC), as well as increases in H 2 O 2 and malondialdehyde contents in roots and leaves. Seed irradiation with He–Ne laser for 20 min significantly improved these parameters, enhancing Pb tolerance. Conversely, the prolonged laser priming (40 min) resulted in less favorable outcomes, including reduced growth, TChl content, and RWC, while also exacerbating oxidative damage to membranes even under non-stressful conditions. The 20-min laser priming systemically mitigated Pb-induced lipid peroxidation and H 2 O 2 accumulation by boosting the activities of superoxide dismutase and catalase and increasing proline content in leaves and roots of milk thistle plants. These findings and multivariate analysis suggest that optimal dose of laser initiates a “stress memory” in seeds which is activated upon subsequent exposure to Pb stress, boosting the plant defensive mechanisms and enabling the plant to better cope with oxidative damage. This study underscore the promising potential of He–Ne laser priming as a novel strategy for increasing heavy metal tolerance in medicinal plants like milk thistle, offering an eco-friendly technique for maintaining their productivity under heavy metal stress.

Lead (Pb) contamination in Moso bamboo forests poses a challenge in terms of sustainable development and raises concerns about the safety of bamboo shoots for consumption. However, the physiological impacts of Pb stress on Moso bamboo growth and the molecular mechanisms governing its adaptive responses remain poorly understood. This study comprehensively investigated the physiological and transcriptomic responses of Moso bamboo to Pb stress. The results showed that low concentrations (1–10 µM) of Pb stress had minimal adverse effects on biomass accumulation and the photochemical quantum yield of PSII in Moso bamboo. However, at a high Pb concentration (50 µM), the growth of roots was significantly inhibited, while Pb accumulation in the roots and shoots reached 15,611 mg·kg−1 and 759 mg·kg−1, respectively. The uptake of Pb was increased as the external Pb concentration increased, but the xylem loading of Pb reached saturation at 57.79 µM after six-hour exposure. Pb was mainly localized in the epidermis and pericycle cells in the roots, where the thickening of cell walls in these cells was found after Pb treatment. Transcriptomic profiling identified 1485 differentially expressed genes (DEGs), with significant alterations in genes associated with metal cation transporters and cell wall synthesis. These findings collectively indicate that Moso bamboo is a Pb-tolerant plant, characterized by a high accumulation capacity and efficient xylem loading. The tolerance mechanism likely involves the transcriptional regulation of genes related to heavy metal transport and cell wall biosynthesis.

Litsea cubeba Pers., a dioecious species, is an important tree species for the bioenergy industry with great potential for lead (Pb)-polluted soil phytoremediation. However, the sex-specific morphological and physiological characteristics of L. cubeba under Pb stress remain largely unknown. In this study, L. cubeba was used as a study model to identify sex differences in leaf traits, chlorophyll, photosynthetic gas parameters, chlorophyll fluorescence, Pb subcellular distribution, and photosynthesis-related nutrient contents in chloroplasts and cell nuclei under three different Pb concentrations [0 (CK), 1 (P1), 2 (P2), and 3 (P3) mmol/kg]. The results indicate that Pb stress significantly decreases photosynthetic leaf pigments in both sexes, mainly caused by changes in Ca, Mg, and Mn contents. Furthermore, L. cubeba male plants exhibited greater adaptability to Pb stress by enlarging their leaf area, enhancing photosynthesis and excess light energy in the form of heat dissipation when compared to female plants. Notably, we observed that more Pb reached the organelle fraction and damaged chloroplasts and mitochondria in female leaves under high-level Pb treatments compared to those of the opposite sex. Transcriptome analysis demonstrated that Pb stress could significantly up-regulate more genes involved in photosynthetic antenna proteins and photosynthesis pathways in male leaves than in female leaves. Taken together, L. cubeba male plants are clearly more resistant to Pb toxicity than female plants—at least under the described Pb treatments—which is most likely due to differences in Pb allocation. This research offers a theoretical foundation for the utilization of male and female L. cubeba as suitable plants for the remediation of Pb-polluted soil.

The aim is to analyze the Pb-tolerance of three commonly found tree species and determine the Pb-toxicity and impacts of Pb on growth, physiological and biochemical parameters. In the present study, we examine the response of Pb-induced stress in three commonly growing tree species i.e., Terminalia arjuna , Cassia fistula , and Pongamia pinnata based on various characteristics at an interval of 90 days for 360 days. Plant seedlings were exposed to 0 (control), 200, 450, and 600 mg of Pb/kg dry soil. Our results showed that Pb significantly reduced growth, photosynthetic pigments, and physiological parameters in all studied species. These reductions were highest in P. pinnata followed by C. fistula , and T. arjuna . Besides, Pb-induced toxicity caused many fold rise in biochemicals such as malondialdehyde, proline, phenolics, thiols, and others. These elevations were highest in T. arjuna followed by C. fistula and P. pinnata . Further, it was also observed that with an increase in the number of days of year (DOY) of Pb exposure, plants showed a reduction in physiological parameters but an increase in growth and biochemical parameters in all studied species. Furthermore, the physiological parameters showed a negative and the biochemical parameters showed a positive correlation with both DOY and treatments, while the growth parameters showed a negative correlation with treatments and a positive correlation with DOY. Hence, we can conclude that the three selected species are promising candidates to be recommended for plantation in Pb-polluted urban areas due to their Pb-tolerance. Overall, the study provides a better understanding of the impacts of Pb on tree species in the long-term and in assessing their potential for sustainable plantations in urban areas. Highlights • Pb reduced growth, and affected physiology and biochemistry in all studied species. • P. pinnata was most affected followed by C. fistula and T. arjuna . • Physiology was diminished with the number of days of Pb exposure and treatments. • Physiology had negative and biochemistry had positive correlation with Pb exposure. • Growth was decreased due to Pb exposure but increased with number of days.

Lead (Pb) soil contamination remains a major ecological challenge. Zygophyllum fabago is a candidate for the Pb phytostabilisation of mining tailings; nevertheless, the cytogenotoxic effects of low doses of Pb on this species are still unknown. Therefore, Z. fabago seeds collected from non-mining (NM) and mining (M) areas were exposed to 0, 5 and 20 µM Pb for four weeks, after which seedling growth, Pb cytogenotoxic effects and redox status were analyzed. The data revealed that Pb did not affect seedling growth in M populations, in contrast to the NM population. Cell cycle progression delay/arrest was detected in both NM and M seedlings, mostly in the roots. DNA damage (DNAd) was induced by Pb, particularly in NM seedlings. In contrast, M populations, which showed a higher Pb content, exhibited lower levels of DNAd and protein oxidation, together with higher levels of antioxidants. Upon Pb exposure, reduced glutathione (GSH) and non-protein thiols were upregulated in shoots and were unaffected/decreased in roots from the NM population, whereas M populations maintained higher levels of flavanols and hydroxycinnamic acids in shoots and triggered GSH in roots and shoots. These differential organ-specific mechanisms seem to be a competitive strategy that allows M populations to overcome Pb toxicity, contrarily to NM, thus stressing the importance of seed provenance in phytostabilisation programs.

Chlorophyll a fluorescence measurement has been used as a probe to examine and compare the tolerance of bryophytes against heavy metals stress caused in field trials and under laboratory conditions. The ratio of variable fluorescence (Fv) to the maximal fluorescence (Fm) in dark-adapted leaves termed as 'maximal photochemical efficiency' of PS II (Fv/Fm) was measured in selected bryophytes to study their quantum efficiency. Tolerance potential for lead (Pb) in bryophytes was evaluated statistically by using Dunkun's Multiple Range Test, which indicates that lead-treated moss Grimmia anodon and liverwort Riccardia pinguis exhibited the most physiological damage of PS II. Conversely, minimal changes were observed in Barbula vinealis and Thuidium cymbifolium. Field trials of all the selected bryophytes exhibited moderate changes in the Fv/Fm ratio except G. anodon and R. pinguis. This variation in susceptibility is due to stress caused by metal pollution. Therefore, it is desirable to study the relative tolerance potential of bryophytes as little is known about their susceptibility to metals. Validated tolerant bryophytes species will have multiple applications in studies of biomapping, forest enrichment and carbon gain.

Heavy metals negatively affect soil quality and crop growth. In this study, we compared the tolerance of six ryegrass cultivars to cobalt (Co2+), lead (Pb2+), and nickel (Ni2+) stresses by analyzing their physiological indexes and transcript levels of genes encoding metal transporters. Compared with the other cultivars, the cultivar Lm1 showed higher germination rates and better growth under Co2+, Pb2+, or Ni2+ treatments. After 48 h of Co2+ treatment, the total antioxidant capacity of all six ryegrass cultivars was significantly increased, especially that of Lm1. In contrast, under Pb2+ stress, total antioxidant capacity of five cultivars was significantly decreased, but that of Lm1 was unaffected at 24 h. Staining with Evans blue dye showed that the roots of Lm1 were less injured than were roots of the other five ryegrass cultivars by Co2+, Pb2+, and Ni2+. Lm1 translocated and accumulated lesser Co2+, Pb2+, and Ni2+ than other cultivars. In Lm1, genes encoding heavy metal transporters were differentially expressed between the shoots and roots in response to Co2+, Pb2+, and Ni2+. The aim of these researches could help find potential resource for phytoremediation of heavy metal contamination soil. The identified genes related to resistance will be useful targets for molecular breeding.

Background Macleaya cordata is a traditional medicinal herb, and it has high tolerance and accumulation ability to heavy metals, which make it a good candidate species for studying phytoremediation. The objectives of this study were to investigate response and tolerance of M. cordata to lead (Pb) toxicity based on comparative analysis of transcriptome and proteome. Results In this study, the seedlings of M. cordata cultured in Hoagland solution were treated with 100 µmol·L − 1 Pb for 1 day (Pb 1d) or 7 days (Pb 7d), subsequently leaves of M. cordata were taken for the determination of Pb accumulation and hydrogen peroxide production (H 2 O 2 ), meanwhile a total number of 223 significantly differentially expressed genes (DEGs) and 296 differentially expressed proteins (DEPs) were screened between control and Pb treatments. The results showed leaves of M. cordata had a special mechanism to maintain Pb at an appropriate level. Firstly, some DEGs were iron (Fe) deficiency-induced transporters, for example, genes of vacuolar iron transporter and three ABC transporter I family numbers were upregulated by Pb, which can maintain Fe homeostasis in cytoplasm or chloroplast. In addition, five genes of calcium (Ca 2+ ) binding proteins were downregulated in Pb 1d, which may regulate cytoplasmic Ca 2+ concentration and H 2 O 2 signaling pathway. On the other hand, the cysteine synthase upregulated, glutathione S-transferase downregulated and glutathione reductase downregulated in Pb 7d can cause reduced glutathione accumulation and decrease Pb detoxification in leaves. Furthermore, DEPs of eight chlorophyll a/b binding proteins, five ATPases and eight ribosomal proteins can play a pivotal role on chloroplast turnover and ATP metabolism. Conclusions Our results suggest that the proteins involved in Fe homeostasis and chloroplast turnover in mesophyll cells may play key roles in tolerance of M. cordata to Pb. This study offers some novel insights into Pb tolerance mechanism of plants, and the potential valuable for environmental remediation of this important medicinal plant.