Responses of soil and rhizosphere microbial communities to Cd-hyperaccumulating willows and Cd contamination.

BACKGROUND: The pollution of soil by heavy metals, particularly Cd, is constitutes a critical international environmental concern. Willow species are renowned for their efficacy in the phytoremediation of heavy metals owing to their high Cd absorption rate and rapid growth. However, the mechanisms underlying microbial regulation for high- and low-accumulating willow species remain poorly understood. Therefore, we investigated the responses of soil and rhizosphere microbial communities to high- and low-Cd-accumulating willows and Cd contamination. We analyzed soil properties were analyzed in bulk soil (SM) and rhizosphere soil (RM) planted with high-accumulating (H) and low-accumulating (L) willow species. RESULTS: Rhizosphere soil for different willow species had more NH4+ than that of bulk soil, and RM-H soil had more than RM-L had. The available phosphorus content was greater in hyper-accumulated species than it was in lower-accumulated species, especially in RM-H. Genome sequencing of bacterial and fungal communities showed that RM-L exhibited the highest bacterial diversity, whereas RM-H displayed the greatest richness than the other groups. SM-L exhibited the highest diversity and richness of fungal communities. Ralstonia emerged as the predominant bacterium in RM-H, whereas Basidiomycota and Cercozoa were the most enriched fungi in SM-H. Annotation of the N and C metabolism pathways revealed differential patterns: expression levels of NRT2, NarB, nirA, nirD, nrfA, and nosZ were highest in RM-H, demonstrating the effects of NO3-and N on the high accumulation of Cd in RM-H. The annotated genes associated with C metabolism indicated a preference for the tricarboxylic pathway in RM-H, whereas the hydroxypropionate-hydroxybutyrate cycle was implicated in C sequestration in SM-L. CONCLUSIONS: These contribute to elucidation of the mechanism underlying high Cd accumulation in willows, particularly in respect of the roles of microbes and N and C utilization. This will provide valuable insights for repairing polluted soil using N and employing organic acids to improve heavy metal remediation efficiency.

Exploring the combined effect of heavy metals on accumulation efficiency of Salix alba raised on lead and cadmium contaminated soils.

The present study illustrated that Salix alba can accumulate high level of Pb and Cd in different plant parts, with maximum accumulation in roots followed by stem and leaves in the order Cd > Pb > Cd + Pb. The phytoremediation evaluation factors such as bioconcentration factor (BCF) and translocation factor (TF) was higher for Cd over Pb in all plant parts, further the BCF for both Pb and Cd was maximum in root (BCF > 1) followed by stem and leaves. Higher accumulation of Cd over the Pb was observed inside the plant tissues due to Cd mimics with other elements and gets transported through respective transporters. The combined treatment of Pb and Cd affected the bioaccumulation at every treatment level suggesting the negative effect among both elements. Higher survival rate (>85%) was recorded up to 200mgPb/kg and 15mgCd/kg, while further increase in metal concentration reduced the plant efficiency to remediate contaminated soils, hence results in declined survival rate. The FTIR analysis revealed that Pb and Cd accumulation in plants induced changes in carboxy, amino, hydroxyl and phosphate groups that ultimately caused alteration in physiological and biochemical processes of plant and thus provided an insight to the interaction, binding and accumulation of heavy metals.

The present study conferred that Salix alba is a heavy metal (Pb and Cd) excluder plant on the basis of phytoremediation efficiency evaluation factors such BCF >1 (root) and TF <1. The correlation studies suggested the negative correlation among Pb and Cd accumulation and morphological traits. Physiological studies indicated that Pb and Cd accumulation negatively affect chlorophyll concentration and the antioxidant mechanism of plants gets activated, further these results are confirmed with FTIR studies, which reported the alteration in functional groups and associated compounds in plant tissues under Pb and Cd stress.

Comparative performance of Populus spp. and Salix spp. for growth, nutrition, and heavy metal uptake in a wastewater hydroponic system.

This research aimed to ascertain the growth, biomass, and phytoremediation capacity of poplars and willow cultivated using wastewater in a hydroponic system. The cuttings were exposed to two water treatments for eight weeks: (1) tap water supply with 1/4 strength Hoagland's solution (TW) as a control and (2) urban raw wastewater with 1/4 strength Hoagland's solution (WW) in a completely randomized experimental design and growth parameters and nutrient and heavy metal content distribution in various plant tissues were assessed. Our results suggest that compared with the TW, seven studied species/clones revealed an increase in growth and biomass parameters (stem height by 16.4%, and root, shoot, and total biomass by 37.3%, 26.9%, and 29.3%, respectively) caused by WW treatment, except the root length and stem diameter that remained the same under two water treatments. Poplars and willow showed a remarkable variability in growth and biomass parameters, with the highest stem diameter, stem height, and root, shoot, and total biomass in Populus nigra L. 62.154. Expression of growth responses to WW treatment with tolerance indices (Tis) indicated the tested poplars and willow as highly tolerant (Ti >100%) with no significant differences among them based on this index. Plant analysis showed that WW treatment increased the concentrations of nutrients and heavy metals in the shoots and roots. Overall, under both water treatments, the capability of the tested species/clones to uptake and accumulate micro-nutrients (except copper (Cu) in shoots) and heavy metals (except chromium (Cr) in shoots) in the plant tissues varied noticeably. However, for all tested plants, the roots had higher concentrations of micro-nutrients (iron (Fe), zinc (Zn), and Cu concentrations in the roots were about 36.8%, 107.6%, and 30.1% of that in the shoots, respectively) and heavy metals (nickel (Ni), Cr, and lead (Pb) concentrations in the roots were about 115.3%, 344.2%, and 198.9% of that in the shoots, respectively), suggesting their capability for micro-nutrients and heavy metals rhizofiltration. Concerning obtained results under hydroponic culture, it can be concluded that these poplars and willow might be promising candidates for wastewater applications. However, data obtained by a hydroponic system need to be confirmed in pot and field experiments.

There are limited studies on the reactions of Salicaceae plants in a wastewater hydroponic system. This research can be considerable for preliminary evaluation of Salicaceae plants to estimate their effectiveness in contaminated soils. Furthermore, the growth, biomass, and phytoremediation responses of Salicaceae plants differ to wastewater application, so this work is important to evaluate the responses of seven different poplar and willow species/clones to municipal wastewater application.

Impact of Heavy Metals on Cold Acclimation of Salix viminalis Roots.

In nature, plants are exposed to a range of climatic conditions. Those negatively impacting plant growth and survival are called abiotic stresses. Although abiotic stresses have been extensively studied separately, little is known about their interactions. Here, we investigate the impact of long-term mild metal exposure on the cold acclimation of Salix viminalis roots using physiological, transcriptomic, and proteomic approaches. We found that, while metal exposure significantly affected plant morphology and physiology, it did not impede cold acclimation. Cold acclimation alone increased glutathione content and glutathione reductase activity. It also resulted in the increase in transcripts and proteins belonging to the heat-shock proteins and related to the energy metabolism. Exposure to metals decreased antioxidant capacity but increased catalase and superoxide dismutase activity. It also resulted in the overexpression of transcripts and proteins related to metal homeostasis, protein folding, and the antioxidant machinery. The simultaneous exposure to both stressors resulted in effects that were not the simple addition of the effects of both stressors taken separately. At the antioxidant level, the response to both stressors was like the response to metals alone. While this should have led to a reduction of frost tolerance, this was not observed. The impact of the simultaneous exposure to metals and cold acclimation on the transcriptome was unique, while at the proteomic level the cold acclimation component seemed to be dominant. Some genes and proteins displayed positive interaction patterns. These genes and proteins were related to the mitigation and reparation of oxidative damage, sugar catabolism, and the production of lignans, trehalose, and raffinose. Interestingly, none of these genes and proteins belonged to the traditional ROS homeostasis system. These results highlight the importance of the under-studied role of lignans and the ROS damage repair and removal system in plants simultaneously exposed to multiple stressors.

Phosphorus deficiency-induced cell wall pectin demethylesterification enhances cadmium accumulation in roots of Salix caprea.

Regions affected by heavy metal contamination frequently encounter phosphorus (P) deficiency. Numerous studies highlight crucial role of P in facilitating cadmium (Cd) accumulation in woody plants. However, the regulatory mechanism by which P affects Cd accumulation in roots remains ambiguous. This study aims to investigate the effects of phosphorus (P) deficiency on Cd accumulation, Cd subcellular distribution, and cell wall components in the roots of Salix caprea under Cd stress. The results revealed that under P deficiency conditions, there was a 35.4% elevation in Cd content in roots, coupled with a 60.1% reduction in Cd content in shoots, compared to the P sufficiency conditions. Under deficient P conditions, the predominant response of roots to Cd exposure was the increased sequestration of Cd in root cell walls. The sequestration of Cd in root cell walls increased from 37.1% under sufficient P conditions to 66.7% under P deficiency, with pectin identified as the primary Cd binding site under both P conditions. Among cell wall components, P deficiency led to a significant 31.7% increase in Cd content within pectin compared to P sufficiency conditions, but did not change the pectin content. Notably, P deficiency significantly increased pectin methylesterase (PME) activity by regulating the expression of PME and PMEI genes, leading to a 10.4% reduction in the degree of pectin methylesterification. This may elucidate the absence of significant changes in pectin content under P deficiency conditions and the concurrent increase in Cd accumulation in pectin. Fourier transform infrared spectroscopy (FTIR) results indicated an increase in carboxyl groups in the root cell walls under P deficiency compared to sufficient P treatment. The results provide deep insights into the mechanisms of higher Cd accumulation in root mediated by P deficiency.

Exogenous hydrogen sulfide and methylglyoxal alleviate cadmium-induced oxidative stress in Salix matsudana Koidz by regulating glutathione metabolism.

BACKGROUND: Cadmium (Cd) is a highly toxic element for plant growth. In plants, hydrogen sulfide (H2S) and methylglyoxal (MG) have emerged as vital signaling molecules that regulate plant growth processes under Cd stress. However, the effects of sodium hydrosulfide (NaHS, a donor of H2S) and MG on Cd uptake, physiological responses, and gene expression patterns of Salix to Cd toxicity have been poorly understood. Here, Salix matsudana Koidz. seedlings were planted in plastic pot with applications of MG (108 mg kg- 1) and NaHS (50 mg kg- 1) under Cd (150 mg kg- 1) stress. RESULTS: Cd treatment significantly increased the reactive oxygen species (ROS) levels and malondialdehyde (MDA) content, but decreased the growth parameters in S. matsudana. However, NaHS and MG supplementation significantly decreased Cd concentration, ROS levels, and MDA content, and finally enhanced the growth parameters. Cd stress accelerated the activities of antioxidative enzymes and the relative expression levels of stress-related genes, which were further improved by NaHS and MG supplementation. However, the activities of monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR) were sharply decreased under Cd stress. Conversely, NaHS and MG applications restored the MDHAR and DHAR activities compared with Cd-treated seedlings. Furthermore, Cd stress decreased the ratios of GSH/GSSG and AsA/DHA but considerably increased the H2S and MG levels and glyoxalase I-II system in S. matsudana, while the applications of MG and NaHS restored the redox status of AsA and GSH and further improved glyoxalase II activity. In addition, compared with AsA, GSH showed a more sensitive response to exogenous applications of MG and NaHS and plays more important role in the detoxification of Cd. CONCLUSIONS: The present study illustrated the crucial roles of H2S and MG in reducing ROS-mediated oxidative damage to S. matsudana and revealed the vital role of GSH metabolism in regulating Cd-induced stress.

Acetic acid enhances drought tolerance more in female than in male willows.

Drought is an important stress factor that limits plant growth and development. Female willows generally display stronger drought tolerance than males. The application of exogenous acetic acid (AA) has emerged as an efficient and eco-friendly approach to facilitate drought tolerance in willows. However, whether AA exerts sexually different effects on willows remains undefined. In this study, we comprehensively performed morphological and physiological analyses on three willow species, Salix rehderiana, Salix babylonica, and Salix matsudana, to investigate the sexually different responses to drought and AA. The results indicated that willow females were more drought-tolerant than males. AA application effectively enhanced willows' drought tolerance, and females applied with AA displayed greater root distribution and activity, stronger osmotic and antioxidant capacity and photosynthetic rate but less reactive oxygen species, or abscisic acid-mediated stomatal closure than males. In addition, AA application enhanced the jasmonic acid signaling pathway in females but inhibited it in males, conferring stronger drought defense capacity in female willows than in males. Overall, AA application improves drought tolerance more in female than in male willows, further enlarging the sexual differences in willows under drought-stressed conditions.

Allochthonous arbuscular mycorrhizal fungi promote Salix viminalis L.-mediated phytoremediation of polycyclic aromatic hydrocarbons characterized by increasing the release of organic acids and enzymes in soils.

Polycyclic aromatic hydrocarbons (PAHs) are well known persistent organic pollutants that have carcinogenic, teratogenic, and mutagenic effects on humans and animals. Arbuscular mycorrhizal fungi (AMF) that can infest plant hosts and form symbioses may help plants to enhance potential rhizosphere effects, thus contributing to the rhizodegradation of PAH-contaminated soils. The present study aimed to assess the effectiveness of AMF on enhancing Salix viminalis-mediated phytoremediation of PAH-polluted soil and clarify the plant enzymatic and organic acid mechanisms induced by AMF. Natural attenuation (NA), phytoremediation (P, Salix viminalis), S. viminalis-AMF combined remediation using willow inoculated with Funneliformis mosseae (PM), Laroideoglomus etunicatum (PE), and Rhizophagus intraradices (PI) were used as strategies for the remediation of PAH-polluted soils. The results showed that AMF inoculation contributed to the dissipation of the high-molecular-weight PAH benzo (α) pyrene that had concentrations in PM, PE, and PI treatments of 40.1 %, 24.49 %, and 36.28 % of the level in the NA treatment, and 62.32 %, 38.05 %, and 56.38 % of the level in the P treatment after 90 days. The mycorrhizal treatment also improved the removal efficiency of phenanthrene and pyrene, as their concentrations were sharply decreased after 30 days compared to the NA and P treatments. The research further clarified the changes in rhizosphere substances induced by AMF. Organic acids including arachidonic acid, octadecanedioic acid, α-linolenic acid, 10,12,14-octadecarachidonic acid and 5-methoxysalicylic acid that can act as co-metabolic substrates for certain microbial species to metabolize PAHs were significantly increased in AMF-inoculated treatments. AMF inoculation also elevated the levels of polyphenol oxidase, laccase, and dehydrogenase, that played crucial roles in PAHs biodegradation. These findings provide an effective strategy for using AMF-assisted S. viminalis to remediate PAH-polluted soils, and the results have confirmed the key roles of organic acids and soil enzymes in plant-AMF combined remediation of PAHs.

A Comparative Analysis of Phytochemicals, Metal Ions, Volatile Metabolites in Heart Wood, Stem Bark and Leaves of Salix alba L. along with in Vitro Antioxidant, Antacid, Antimicrobial Activities for Sake of Environment Conservation by Substitution of Stem Bark With Leaf.

The genus of Salix is used in food, medicine and nutraceuticals, and standardized by using the single marker compound Salicin only. Stem bark is the official part used for the preparation of various drugs, nutraceuticals and food products, which may lead to overexploitation and damage of tree. There is need to search substitution of the stem bark with leaf of Salix alba L. (SA), which is yet not reported. Comparative phytochemicals viz. Salicin, Procyanidin B1 and Catechin were quantified in the various parts of SA viz. heart wood (SA-HW), stem bark (SA-SB) and leaves (SA-L) of Salix alba L.by using newly developed HPLC method. It was observed that SA-HW and SA-L contained far better amount of Salicin, Procyanidin B and Catechin as compared to SA-SB (SA-HW~SA-L≫SA-SB). Essential and toxic metal ions of all three parts were analysed using newly developed ICP-OES method, where SA-L were founded as a rich source of micronutrients and essential metal ions as compared to SA-SB and SA-HW. GC-MS analysis has shown the presence of fatty acids and volatile compounds. The observed TPC and TFC values for all three parts were ranged from 2.69 to 32.30 mg GAE/g of wt. and 37.57 to 220.76 mg QCE/g of wt. respectively. In DPPH assay the IC50 values of SA-SB, SA-HW, and SA-L were 1.09 (±0.02), 5.42 (±0.08), and 8.82 (±0.10) mg/mL, respectively. The order of antibacterial activities against E. coli, S. aureus, P. aeruginosa, and B. subtilis strains was SA-L>SA-HW>SA-SB with strong antibacterial activities against S. aureus, and B. subtilis strains. The antacid activities order was SA-L>SA-SB>SA-HW. The leaves of SA have shown significant source of nutrients, phytochemicals and medicinal properties than SA-HW and SA-SB. The leaves of SA may be considered as substitute of stem bark to save the environment or to avoid over exploitation, but after the complete pharmacological and toxicological studies.

"Willow Branch" DNA Self-Assembly for Cancer Dual-Target and Proliferation Inhibition.

DNA nanotechnology is beginning to yield unique advantages in the area of drug delivery. For the dual-targeting and proliferation suppression of cancer cells, a "willow branch" DNA assembly based on rolling circle amplification (RCA) was built. Three single-stranded DNAs, including antibody modified cDNAs, aptamer cDNAs, and simple cDNAs, were employed in the DNA self-assembly, along with the RCA scaffolds (every 63 bases is a repeat unit). "Willow branch" DNA (WB DNA) assembly successfully linked multiple antibodies and aptamers together to achieve dual targeting of cancer cells. Binding of CD44 antibodies and S2.2 aptamers to receptors on the cell membrane inhibits both pathways, ß-catenin signaling and nuclear factor-kappa B-specific transcription activity, through feedback regulation. Results demonstrated that WB DNA assembly could effectively exert multivalency clustering cell-surface receptors, modulating signal pathways and inhibiting proliferation. This study proposes a new approach for cancer dual-target and proliferation inhibition by clustering multivalent receptors.

Comparison of two willow genotypes reveals potential roles of iron-regulated transporter 9 and heavy-metal ATPase 1 in cadmium accumulation and resistance in Salix suchowensis.

Willows (Salix spp.) are promising extractors of cadmium (Cd), with fast growth, high biomass production, and high Cd accumulation capacity. However, the molecular mechanisms underlying Cd uptake and detoxification are currently poorly understood. Analysis of the Cd uptake among 30 willow genotypes in hydroponic systems showed that the S. suchowensis and S. integra hybrids, Jw8-26 and Jw9-6, exhibited distinct Cd accumulation and resistance characteristics. Jw8-26 was a high Cd-accumulating and tolerant willow, while Jw9-6 was a low Cd-accumulating and relatively Cd-intolerant willow. Therefore, these two genotypes were ideal specimens for determining the molecular mechanisms of Cd uptake and detoxification. To identify relevant genes in Cd handling, the parent S. suchowensis was treated with Cd and RNA-seq analysis was performed. SsIRT, SsHMA, and SsGST, in addition to the transcription factors SsERF, SsMYB, and SsZAT were identified as being associated with Cd uptake and resistance. Because membrane-localised heavy metal transporters mediate Cd transfer to plant tissues, a total of 17 SsIRT and 12 SsHMA family members in S. suchowensis were identified. Subsequently, a thorough bioinformatics analysis of the SsIRT and SsHMA families was conducted, and their transcript levels were analysed in the roots of the two hybrids. The transcript levels of SsIRT9 in roots were positively correlated with the observed differences in Cd accumulation in Jw8-26 versus Jw9-6. Jw8-26 displayed higher SsIRT9 expression levels and higher Cd accumulation than Jw9-6; therefore, SsIRT9 may be involved in Cd uptake. Gene expression analysis also revealed that SsHMA1 was a candidate gene associated with Cd resistance. These results lay the foundation for understanding the molecular mechanism of Cd transfer and detoxification in willows, and provide guidance for the screening and breeding of high Cd-accumulating and tolerant willow genotypes via genetic engineering.

Plant cadmium resistance 6 from Salix linearistipularis (SlPCR6) affects cadmium and copper uptake in roots of transgenic Populus.

Phytoextraction in phytoremediation is one of the environmentally friendly methods used for restoring soils contaminated by heavy metals (HMs). The screening and identification of HM-resistant plants and their regulatory genes associated with HM ion transport are the key research aims in this field. In this study, a plant cadmium (Cd) resistance (PCR) gene family member, SlPCR6, was identified in roots of Salix linearistipularis, which exhibits strong HM resistance. The results revealed that SlPCR6 expression was induced in S. linearistipularis roots in response to Cd stress. Furthermore, SlPCR6 was mainly localized on the plasma membrane. Compared with the wild type, SlPCR6 overexpression reduced the Cd and copper (Cu) contents in the transgenic poplar (84 K) and increased its Cd and Cu resistance. The roots of transgenic poplar seedlings had lower net Cd and Cu uptake rates than wild type roots. Further investigation revealed that the transcript levels of multiple HM ion transporters were not significantly different between the roots of the wild type and those of the transgenic poplar. These results suggest that SlPCR6 is directly involved in Cd and Cu transport in S. linearistipularis roots. Therefore, SlPCR6 can serve as a candidate gene to improve the phytoextraction of the HMs Cd and Cu through genetic engineering.

Frequent ploidy changes in Salicaceae indicates widespread sharing of the salicoid whole genome duplication by the relatives of Populus L. and Salix L.

BACKGROUNDS: Populus and Salix belong to Salicaceae and are used as models to investigate woody plant physiology. The variation of karyotype and nuclear DNA content can partly reflect the evolutionary history of the whole genome, and can provide critical information for understanding, predicting, and potentially ameliorating the woody plant traits. Therefore, it is essential to study the chromosome number (CN) and genome size in detail to provide information for revealing the evolutionary process of Salicaceae. RESULTS: In this study, we report the somatic CNs of seventeen species from eight genera in Salicaceae. Of these, CNs for twelve species and for five genera are reported for the first time. Among the three subfamilies of Salicaceae, the available data indicate CN in Samydoideae is n = 21, 22, 42. The only two genera, Dianyuea and Scyphostegia, in Scyphostegioideae respectively have n = 9 and 18. In Salicoideae, Populus, Salix and five genera closely related to them (Bennettiodendron, Idesia, Carrierea, Poliothyrsis, Itoa) are based on relatively high CNs from n = 19, 20, 21, 22 to n = 95 in Salix. However, the other genera of Salicoideae are mainly based on relatively low CNs of n = 9, 10, 11. The genome sizes of 35 taxa belonging to 14 genera of Salicaceae were estimated. Of these, the genome sizes of 12 genera and all taxa except Populus euphratica are first reported. Except for Dianyuea, Idesia and Bennettiodendron, all examined species have relatively small genome sizes of less than 1 pg, although polyploidization exists. CONCLUSIONS: The variation of CN and genome size across Salicaceae indicates frequent ploidy changes and a widespread sharing of the salicoid whole genome duplication (WGD) by the relatives of Populus and Salix. The shrinkage of genome size after WGD indicates massive loss of genomic components. The phylogenetic asymmetry in clade of Populus, Salix, and their close relatives suggests that there is a lag-time for the subsequent radiations after the salicoid WGD event. Our results provide useful data for studying the evolutionary events of Salicaceae.

Phytoremediation of aniline by Salix babylonica cuttings: Removal, accumulation, and photosynthetic response.

Aniline, a synthetic compound widely used in industrial and pesticide production, is a potential environmental pollutant. The removal of aniline is extremely important to minimize threats to human health and the surrounding environment. The objectives of this study were to investigate the removal efficiency and physiological response of Salix. babylonica cuttings to aniline pollution. Photosynthesis, chlorophyll fluorescence, spectral reflectance and the concentration of aniline in leaves, stems and roots were analysed. The experiment showed that S. babylonica has a strong removal effect on aniline wastewater. Cuttings from S. babylonica stems and roots played an important role in accumulating aniline. However, this increase in aniline concentration was dose dependent and was not always linear. With increasing aniline concentration in S. babylonica was increasingly stressed, with negative impacts on photosynthesis, chlorophyll fluorescence and spectral reflectance index in S. babylonica leaves. These results indicate that non-stomatal limitations are the main reason for the reduction in Pn in S. babylonica leaves due to chlorophyll structure destruction under aniline stress. In addition, aniline concentrations result in an unbalanced distribution of excitation energy between the two light systems, thereby hindering photosynthetic electron transfer and restricting the efficient operation of photosynthesis. Salix babylonica can endure moderate concentrations of aniline and has potential for the phyto-management of aniline-polluted wastewater, although further studies are needed using polluted wastewater.

Characterisation of early responses in lead accumulation and localization of Salix babylonica L. roots.

BACKGROUND: Lead (Pb) is a harmful pollutant that disrupts normal functions from the cell to organ levels. Salix babylonica is characterized by high biomass productivity, high transpiration rates, and species specific Pb. Better understanding the accumulating and transporting Pb capability in shoots and roots of S. babylonica, the toxic effects of Pb and the subcellular distribution of Pb is very important. RESULTS: Pb exerted inhibitory effects on the roots and shoots growth at all Pb concentrations. According to the results utilizing inductively coupled plasma atomic emission spectrometry (ICP-AES), S. babylonica can be considered as a plant with great phytoextraction potentials as translocation factor (TF) value > 1 is observed in all treatment groups throughout the experiment. The Leadmium™ Green AM dye test results indicated that Pb ions initially entered elongation zone cells and accumulated in this area. Then, ions were gradually accumulated in the meristem zone. After 24 h of Pb exposure, Pb accumulated in the meristem zone. The scanning electron microscopy (SEM) and energy-dispersive X-ray analyses (EDXA) results confirmed the fluorescent probe observations and indicated that Pb was localized to the cell wall and cytoplasm. In transverse sections of the mature zone, Pb levels in the cell wall and cytoplasm of epidermal cells was the lowest compared to cortical and vessel cells, and an increasing trend in Pb content was detected in cortical cells from the epidermis to vascular cylinder. Similar results were shown in the Pb content in the cell wall and cytoplasm of the transverse sections of the meristem. Cell damage in the roots exposed to Pb was detected by propidium iodide (PI) staining, which was in agreement with the findings of Pb absorption in different zones of S. babylonica roots under Pb stress. CONCLUSION: S. babylonica L. is observed as a plant with great potential of Pb-accumulation and Pb-tolerance. The information obtained here of Pb accumulation and localization in S. babylonica roots can furthers our understanding of Pb-induced toxicity and its tolerance mechanisms, which will provide valuable and scientific information to phytoremediation investigations of other woody plants under Pb stress.

Effect of biochar and redmud amendment combinations on Salix triandra growth, metal(loid) accumulation and oxidative stress response.

Remediation of metal(loid) polluted soils is an important area of research nowadays. In particular, one remediation technique is much studied, phytomanagement. Phytomanagement combines amendment application and plant growth in order to reduce the risk posed by contaminants. Salicaceae plants showed tolerance towards metal(loid)s and the ability to accumulate high amounts of metal(loid)s in their tissue. Amendments are often applied to counterbalance the reduced soil fertility and high metal(loid) concentrations. Two amendments gathered attention over the last decades, biochar (product of biomass pyrolysis), which can be activated for better effects, and redmud (by-product of alumina production). Those two amendments showed ability to improve soil conditions and thus plant growth, although few studied their combined application. Moreover, since metal(loid)s are known to induce the overproduction of reactive oxygen species, it is important to measure the level of oxidative stress in the plant, to which plants respond using enzymatic and non-enzymatic systems. But no studies evaluate the response of Salicaceae plants to metal(loid) stress and amendment application at the biochemical level in a real soil condition. Therefore, a mesocosm study was set up to evaluate the effect of amending a mine soil with redmud combined to diverse biochars on the soil properties and Salix triandra growth, metal(loid) accumulation and stress marker levels. Results showed that all amendment combinations improved the soil fertility, reduced metal(loid) mobility and thus ameliorated Salix triandra growth, which accumulated metal(loid)s mainly in its roots. Moreover, among the different amendment combinations, Salix triandra plants still suffered from oxidative stress when grown on PG soil amended with redmud and chemical activated carbon, showing elevated levels of phenolic compounds and salicinoids and important antioxidant and enzymatic activities. Finally, one treatment showed levels of these stress markers similar or lower than the control, the combination of redmud with steam activated carbon. In conclusion, this treatment seemed a good solution in a phytomanagement strategy using Salix triandra, improving soil conditions and plant growth and reducing oxidative stress level in the plant roots.

Accumulation and effects of perfluoroalkyl substances in three hydroponically grown Salix L. species.

The potential of young rooted cuttings of three Salix L. species plants to accumulate a mixture of eleven perfluoroalkyl substances (PFASs), in particular, perfluoroalkyl acids (PFAAs), from the nutrient solution and their effects on plant growth and photosynthesis were assessed in an 8-day experiment. The growth rate of the willow plants exposed to the PFAA mixture was not much affected except for S. triandra. Regarding photosynthesis, the gas exchange parameters were affected more than those related to chlorophyll fluorescence, with significant increase of the net CO2 assimilation rate and parameters related to stomatal conductance. A decreasing trend in the PFAA concentration in leaves with increasing carbon chain length was observed, whereas long-chain PFAAs showed higher concentrations in roots. Accordingly, the foliage to root concentration factor highlighted that PFAAs with shorter carbon chain length (C ≤ 7) translocated and accumulated relatively more in leaves compared to roots. Removal efficiency of individual PFAAs for leaves and roots were comparatively higher with S. eleagnos and S. purpurea than S. triandra, with mean removal values at the whole plant level ranging around 10% of the amount initially spiked, suggesting their potential for phytoremediation of PFASs.

Lead transfer into the vegetation layer growing naturally in a Pb-contaminated site.

The lead was one of the main elements in the glazes used to colour ceramic tiles. Due to its presence, ceramic sludge has been a source of environmental pollution since this dangerous waste has been often spread into the soil without any measures of pollution control. These contaminated sites are often located close to industrial sites in the peri-urban areas, thus representing a considerable hazard to the human and ecosystem health. In this study, we investigated the lead transfer into the vegetation layer (Phragmites australis, Salix alba and Sambucus nigra) growing naturally along a Pb-contaminated ditch bank. The analysis showed a different lead accumulation among the species and their plant tissues. Salix trees were not affected by the Pb contamination, possibly because their roots mainly develop below the contaminated deposit. Differently, Sambucus accumulated high concentrations of lead in all plant tissues and fruits, representing a potential source of biomagnification. Phragmites accumulated large amounts of lead in the rhizomes and, considering its homogeneous distribution on the site, was used to map the contamination. Analysing the Pb concentration within plant tissues, we got at the same time information about the spread, the history of the contamination and the relative risks. Finally, we discussed the role of natural recolonizing plants for the soil pollution mitigation and their capacity on decreasing soil erosion and water run-off.

Corticular photosynthesis drives bark water uptake to refill embolized vessels in dehydrated branches of Salix matsudana.

It is well known that xylem embolism can be repaired by bark water uptake and that the sugar required for embolism refilling can be provided by corticular photosynthesis. However, the relationship between corticular photosynthesis and embolism repair by bark water uptake is still poorly understood. In this study, the role of corticular photosynthesis in embolism repair was assessed using Salix matsudana branch segments dehydrated to -1.9 MPa (P50 , water potential at 50% loss of conductivity). The results indicated that corticular photosynthesis significantly promoted water uptake and nonstructural carbohydrate (NSC) accumulation in the bark and xylem during soaking, thereby effectively enhancing the refilling of the embolized vessels and the recovery of hydraulic conductivity. Furthermore, the influence of the extent of dehydration on the embolism refilling enhanced by corticular photosynthesis was investigated. The enhanced refilling effects were much higher in the mildly dehydrated (-1.5 MPa) and moderately dehydrated (-1.9 MPa) branch segments than in the severely dehydrated (-2.2 MPa) branch segments. This study provides evidence that corticular photosynthesis plays a crucial role in xylem embolism repair by bark water uptake for mildly and moderately dehydrated branches.

Xenobiotics metabolization in Salix alba leaves uncovered by mass spectrometry imaging.

INTRODUCTION: Micropollutants are increasingly monitored as their presence in the environment is rising due to human activities, and they are potential threats to living organisms. OBJECTIVES: This study aimed at understanding the role of plants in xenobiotics removal from polluted environments by following xenobiotics metabolism in leaf tissues. METHODS: Different classes of micropollutants were investigated using liquid chromatography (LC) coupled to quadrupole-time of flight (Q-TOF) high resolution mass spectrometry (HRMS). The tissue localization of xenobiotics in the leaves of a spontaneous (not planted by humans) Salix alba growing near the water flux was further investigated using matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). RESULTS: The LC-Q-TOF analysis revealed the distribution of micropollutants in three different compartments of a tertiary treatment wetland. When further investing the metabolic profile of S. alba leaves using MSI, different distribution patterns were observed in specific leaf tissues. Xenobiotic metabolites were predicted and could also be tentatively identified in S. alba leaves, shedding new light on the metabolic processes at play in leaves to manage xenobiotics uptake from a polluted environment. CONCLUSION: Using complementary metabolomics approaches, this study performed a large-scale exploration of micropollutants spreading in the environment at the exit of a tertiary treatment wetland. The use of MSI coupled with the prediction of xenobiotic metabolites yielded novel insights into plant metabolism during chronical exposure to low doses of a mixture of micropollutants.