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• S. alfredii may be a phytoremediation material for HCMHMs soil. • Heavy metals migrated to rhizosphere soil and were mainly concentrated in roots and leaves by S. alfredii. • Bacteria increased the abundance of some quorum sensing signaling molecules under HCMHMs stress. • Bacteria promoted the path expression that converts serine to cysteine under HCMHMs stress. Pollution accident of nonferrous metallurgy industry often lead to serious heavy metal pollution of the surrounding soil. Phytoremediation of contaminated soil is an environmental and sustainable technology, and soil native microorganisms in the process of phytoremediation also participate in the remediation of heavy metals. However, the effects of high concentrations of multiple heavy metals (HCMHMs) on plants and native soil microorganisms remain uncertain. Thus, further clarification of the mechanism of phytoremediation of HCMHMs soil by plants and native soil microorganisms is required. Using the plant Sedum alfredii (S. alfredii) to restore HCMHM-contaminated soil, we further explored the mechanism of S. alfredii and native soil microorganisms in the remediation of HCMHM soils. The results showed that (i) S. alfredii can promote heavy metals from non-rhizosphere soil to rhizosphere soil, which is conducive to the effect of plants on heavy metals. In addition, it can also enrich the absorbed heavy metals in its roots and leaves; (ii) native soil bacteria can increase the abundance of signal molecule-synthesizing enzymes, such as trpE, trpG, bjaI, rpfF, ACSL , and yidC , and promote the expression of the pathway that converts serine to cysteine, then synthesize substances to chelate heavy metals. In addition, we speculated that genes such as K19703, K07891, K09711, K19703, K07891, and K09711 in native bacteria may be involved in the stabilization or absorption of heavy metals. The results provide scientific basis for S. alfredii to remediate heavy metals contaminated soils, and confirm the potential of phytoremediation of HCMHM contaminated soil. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hyperaccumulators are the material basis and key to the phytoremediation of heavy metal contaminated soils. Conventional methods for screening hyperaccumulators are highly dependent on the time- and labor-consuming sampling and chemical analysis. In this study, a novel spectral approach assisted with multi-task deep learning was proposed to streamline accumulating ecotype screening, heavy metal stress discrimination, and heavy metals quantification in plants. The significant Cd/Zn co-hyperaccumulator Sedum alfredii and its non-accumulating ecotype were stressed by Cd, Zn, and Pb. Spectral images of leaves were rapidly acquired by hyperspectral imaging. The self-designed deep learning architecture was composed of a shallow network (ENet) for accumulating ecotype identification, and a multi-task network (HMNet) for heavy metal stress type and accumulation prediction simultaneously. To further assess the robustness of the networks, they were compared with conventional machine learning models (i.e., partial least squares (PLS) and support vector machine (SVM)) on a series of evaluation metrics of classification, multi-label classification, and regression. S. alfredii with heavy metals accumulation capability was identified by ENet with 100 % accuracy. HMNet reduced overfitting and outperformed machine learning models with the average exact match ratio (EMR) of heavy metal stress discrimination increased by 7.46 %, and residual prediction deviations (RPD) of heavy metal concentrations prediction increased by 53.59 %. The method succeeded in rapidly and accurately discriminating heavy metal stress with EMRs over 91 % and accuracies over 96 %, and in predicting heavy metals accumulation with an average RPD of 3.29 for Zn, 2.57 for Cd, and 2.53 for Pb, indicating the satisfactory practicability and potential for sensing heavy metals accumulation. This study provides a relatively novel spectral method to facilitate hyperaccumulator screening and heavy metals accumulation prediction in the phytoremediation process.

Understanding the defensive strategies of hyperaccumulators in plant–herbivore interactions is essential for their safe applications in phytoremediation. Sedum alfredii plants are widely applied in metal-contaminated soil where they were found to be easily damaged by herbivores. Thus, we investigated a comparative analysis of the defensive strategies from the perspective of constitutive leafy volatiles between the hyperaccumulator S. alfredii plant and its non-hyperaccumulator counterpart, along with feeding preference tests. Generalist snails prefer hyperaccumulators with lower content of metals while detested non-hyperaccumulators with relatively high food qualities in saccharides. Further leafy volatile profiles of the two ecotypes showed a total of 34 differentially enriched metabolites with 16 down-regulated organic compounds in the hyperaccumulators. KEGG pathway enrichment analysis showed two down-regulated metabolic pathways in phenylalanine metabolism and metabolic pathways due to the lower production of naphthalene and benzeneacetaldehyde, which are known herbivore deterrents and predator attractants. Hence, the high reliance on metals with the reduced performance of organic defense implied a trade-off between the two defensive strategies in the hyperaccumulator S. alfredii plants. Overall, this increased susceptibility to herbivores due to the lack of metals advocates the concerns and solutions for the safe application of this species in the phytoremediation practice. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) contamination of agricultural soils poses a potential public health issue for humans. Phytoremediation-based accumulating plants are an effective and sustainable technology for Cadmium remediation of contaminated agricultural soil. The rhizosphere microbiome can promote the growth and Cadmium accumulation in hyperaccumulators, but its taxonomic and functional traits remain elusive. The present study used two ecotypes of Sedum alfredii, an accumulating ecotype (AE) and a non-accumulating ecotype (NAE), as model plants to investigate the rhizosphere microbiome assemblages and influence on plant growth under high cadmium conditions. Our results showed that distinct root microbiomes assembled in association with both ecotypes of S. alfredii and that the assemblages were based largely on the lifestyles of the two ecotypes. In addition, we demonstrated that the functions of the microbes inhabiting the rhizosphere soils were closely associated with root-microbe interactions in both ecotypes of S. alfredii. Importantly, our results also demonstrated that the rhizosphere microbiome assembled in the AE rhizosphere soils contributed to plant growth and cadmium uptake under high cadmium conditions through functions such as nitrogen fixation, phosphorus solubilization, indole acetic acid (IAA) synthesis, and siderophore metabolism. However, this phenomenon was not clearly observed in the NAE. Our results suggest that the rhizosphere microbiome plays important roles in biogeochemical nutrient and metal cycling that can contribute to host plant fitness. [ABSTRACT FROM AUTHOR]

Concerns regarding inevitable soil translocation and bioaccumulation of cadmium (Cd) in plants have been escalating in concomitance with the posed phytotoxicity and threat to human health. Exhibiting a Cd tolerance, Bacillus sp. M6 strain has been reported as a soil amendment owing to its capability of reducing metal bioavailability in soils. The present study investigated the rhizospheric bacterial community of the Cd hyperaccumulator Sedum alfredii using 16S rRNA gene sequencing. Additionally, the Cd removal efficiency of strain Bacillus sp. M6 was enhanced by supplementing with biochar (C), glutamic acid (G), and rhamnolipid (R) to promote the phytoremediation effect of hyperaccumulator S. alfredii. To the best of our knowledge, this is the first time the amendments such as C, G, and R together with the plant-microbe system S. alfredii-Bacillus sp. M6 has been used for Cd bioremediation. The results showed that soil CaCl2 and DTPA (Diethylenetriamine pentaacetic acid) extractable Cd increased by 52.77 and 95.08%, respectively, in all M6 treatments compared to unamended control (CK). Sedum alfredii with Bacillus sp. M6 supplemented with biochar and rhamnolipid displayed a higher phytoremediation effect, and the removal capability of soil Cd (II) reached up to 16.47%. Moreover, remediation of Cd polluted soil by Bacillus sp. M6 also had an impact on the soil microbiome, including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and cadmium transporting ATPase (cadA) genes. Quantitative PCR analysis confirmed the Bacillus sp. M6 strain increased the abundance of AOB and cadA in both low Cd (LC) and high Cd (HC) soils compared to AOA gene abundance. Besides, the abundance of Proteobacteria and Actinobacteria was found to be highest in both soils representing high tolerance capacity against Cd. While Firmicutes ranked third, indicating that the additionof strain could not make it the most dominant species. The results suggested the presence of the hyperaccumulator S. alfredii and Cd tolerant strain Bacillus sp. M6 supplemented with biochar, and rhamnolipid, play a unique and essential role in the remediation process and reducing the bioavailability of Cd. [ABSTRACT FROM AUTHOR]

Concerns regarding inevitable soil translocation and bioaccumulation of cadmium (Cd) in plants have been escalating in concomitance with the posed phytotoxicity and threat to human health. Exhibiting a Cd tolerance, Bacillus sp. M6 strain has been reported as a soil amendment owing to its capability of reducing metal bioavailability in soils. The present study investigated the rhizospheric bacterial community of the Cd hyperaccumulator Sedum alfredii using 16S rRNA gene sequencing. Additionally, the Cd removal efficiency of strain Bacillus sp. M6 was enhanced by supplementing with biochar (C), glutamic acid (G), and rhamnolipid (R) to promote the phytoremediation effect of hyperaccumulator S. alfredii. To the best of our knowledge, this is the first time the amendments such as C, G, and R together with the plant-microbe system S. alfredii-Bacillus sp. M6 has been used for Cd bioremediation. The results showed that soil CaCl2 and DTPA (Diethylenetriamine penta-acetic acid) extractable Cd increased by 52.77 and 95.08%, respectively, in all M6 treatments compared to unamended control (CK). Sedum alfredii with Bacillus sp. M6 supplemented with biochar and rhamnolipid displayed a higher phytoremediation effect, and the removal capability of soil Cd (II) reached up to 16.47%. Moreover, remediation of Cd polluted soil by Bacillus sp. M6 also had an impact on the soil microbiome, including ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and cadmium transporting ATPase (cadA) genes. Quantitative PCR analysis confirmed the Bacillus sp. M6 strain increased the abundance of AOB and cadA in both low Cd (LC) and high Cd (HC) soils compared to AOA gene abundance. Besides, the abundance of Proteobacteria and Actinobacteria was found to be highest in both soils representing high tolerance capacity against Cd. While Firmicutes ranked third, indicating that the additionof strain could not make it the most dominant species. The results suggested the presence of the hyperaccumulator S. alfredii and Cd tolerant strain Bacillus sp. M6 supplemented with biochar, and rhamnolipid, play a unique and essential role in the remediation process and reducing the bioavailability of Cd.

Hyperaccumulators are the material basis and key to the phytoremediation of heavy metal contaminated soils. Conventional methods for screening hyperaccumulators are highly dependent on the time- and labor-consuming sampling and chemical analysis. In this study, a novel spectral approach assisted with multi-task deep learning was proposed to streamline accumulating ecotype screening, heavy metal stress discrimination, and heavy metals quantification in plants. The significant Cd/Zn co-hyperaccumulator Sedum alfredii and its non-accumulating ecotype were stressed by Cd, Zn, and Pb. Spectral images of leaves were rapidly acquired by hyperspectral imaging. The self-designed deep learning architecture was composed of a shallow network (ENet) for accumulating ecotype identification, and a multi-task network (HMNet) for heavy metal stress type and accumulation prediction simultaneously. To further assess the robustness of the networks, they were compared with conventional machine learning models (i.e., partial least squares (PLS) and support vector machine (SVM)) on a series of evaluation metrics of classification, multi-label classification, and regression. S. alfredii with heavy metals accumulation capability was identified by ENet with 100 % accuracy. HMNet reduced overfitting and outperformed machine learning models with the average exact match ratio (EMR) of heavy metal stress discrimination increased by 7.46 %, and residual prediction deviations (RPD) of heavy metal concentrations prediction increased by 53.59 %. The method succeeded in rapidly and accurately discriminating heavy metal stress with EMRs over 91 % and accuracies over 96 %, and in predicting heavy metals accumulation with an average RPD of 3.29 for Zn, 2.57 for Cd, and 2.53 for Pb, indicating the satisfactory practicability and potential for sensing heavy metals accumulation. This study provides a relatively novel spectral method to facilitate hyperaccumulator screening and heavy metals accumulation prediction in the phytoremediation process. [Display omitted] • A novel spectral approach to facilitate hyperaccumulator screening was established. • Simultaneous monitoring of ecotypes, heavy metal stress and accumulation in plants. • Self-designed multi-task deep learning method is better than PLS and SVM models. • The heavy metal accumulating ecotype was perfectly discriminated. • Cd, Zn, and Pb accumulation in S. alfredii was rapidly and accurately assessed. [ABSTRACT FROM AUTHOR]

Hyperaccumulating ecotype (HE) of Sedum alfredii Hance is a Zn/Cd hyperaccumulator, which can accumulate Zn in shoot up to 2% of dry weight, understanding the mechanism of Zn tolerance and accumulation can improve its application in phytoremediation. In this study, the function of two metal tolerance protein (MTP) genes of HE plants (SaMTP2h and SaMTP3h) was comparatively analyzed with the known SaMTP1. Three transporters could complement Zn sensitivity in yeast mutant in different levels. mRNA level of SaMTP1 in shoot was constitutively and highly expressed which was thousands of times of other two genes. mRNA level of SaMTP1 was not affected by Zn/Cd treatment, while mRNA levels of SaMTP2h and SaMTP3h were up-regulated by 50 µM Cd or 500 µM Zn treatment. SaMTP2h was significantly higher expressed in young leaves while SaMTP1 and SaMTP3h were relatively equally expressed in different leaves; SaMTP1 was higher expressed in mesophyll and SaMTP3h was significantly higher expressed in epidermis. Overexpression of SaMTP1, SaMTP2h or SaMTP3h significantly enhanced Zn tolerance and accumulation in tobacco plants and complemented Zn sensitivity in Arabidopsis mtp1-1 mutant. In conclusion, our study revealed that three MTPs could play significant but different roles in Zn accumulation and tolerance in HE plants. [ABSTRACT FROM AUTHOR]

Soil cadmium (Cd) extraction for hyperaccumulators is one of the most important technologies for the remediation of Cd-contaminated farmland soil. However, a phytoremediation model using a single hyperaccumulator cannot guarantee normal agricultural production in contaminated areas. To solve this problem, a combination of efficient remediation and safe production has been developed. Based on two-period field experiments, this study explored the effect of biofortification on soil Cd remediation using the fruit tree Sedum alfredii Hance and oil sunflower crop rotation and relay cropping mode. BioA and BioB treatments could markedly improve the efficiency of Cd extraction and remediation, and the maximum increase in Cd accumulation was 243.29%. When BioB treatment was combined with papaya–S. alfredii and oil sunflower crop rotation and relay cropping mode, the highest soil Cd removal rate in the two periods was 40.84%, whereas the Cd concentration of papaya fruit was lower than safety production standards (0.05 mg/kg). These results demonstrate that biofortification measures can significantly improve the Cd extraction effect of S. alfredii crop rotation and relay cropping restoration modes, which has guiding significance for Cd pollution remediation and safe production in farmland.

Quorum sensing (QS) plays an important role in the intensive communication between plants and microbes in the rhizosphere during the phytoremediation. This study explored the influence of the root exudates of hyperaccumulator Sedum alfredii on Pseudomonas aeruginosa based on QS. The effects of the components of root exudates, genes expression and transcription regulation of QS system (especially the las system) in Pseudomonas aeruginosa wild-type strain (WT) and rhl system mutant strain (ΔrhlI) were systematically analyzed and discussed. The WT and ΔrhlI exposed to gradient root exudates (0×, 1×, 2×, 5× and 10×) showed a concentration-corrective inhibition on protease production, with the inhibition rates of 51.4–74.5% and 31.2–50.0%, respectively. Among the components of the root exudates of Sedum alfredii, only thymol had an inhibition effects to the root exudates on the activity of protease and elastase. The inhibition rates of 50 μmol/L thymol on protease and elastase in WT were 44.7% and 24.3%, respectively, which was consistent with the variation in ΔrhlI. The gene expression of lasB declined 36.0% under the 1× root exudate treatment and 73.0% under the 50 μmol/L thymol treatment. Meanwhile, there was no significant impact on N-3-oxo-dodecanoyl-L-homoserine lactone signal production and the gene expression of lasI and lasR. Therefore, thymol from Sedum alfredii root exudates could inhibit the formation of protease and elastase in Pseudomonas aeruginosa by suppressing the expression of lasB, without any significant influence on the main las system as a potential natural QS inhibitor.

Application of activating agents can significantly improve efficiency of plants for remediation of soils contaminated by heavy metals, however, damage to soil and plants limits application of traditional activating agents. The aim of our experiments is to select an efficient,green and low-cost activating agent to improve efficiency of plant extraction technology. In this study, contaminated soil was remediated by Sedum alfredii. The effects of two plant extracts (i.e., Oxalis corniculata,OX and Medicago sativaextract, ME) in addition to citric acid (CA) were studied in oscillatory activation experiment and pot experiment. The oscillation activation experiment revealed that extraction quantity of heavy metals in the soil was enhanced significantly with concentration of plant extract. The extraction quantity of Zn from 100% OX extract and ME extract were significantly higher than 10 mmol/L CA (54.04% and 33.09%, respectively). The 10 mmol/L CA has best extraction efficiency for Cd, up to 41.36 µg/kg, which is significantly higher than CK (control) (p

Hyperaccumulators are the preferred materials for phytoremediation. Sedum alfredii Hance is a cadmium (Cd) hyperaccumulator plant in China, although its detoxification mechanism remains unresolved. In our study, we cloned a gene belonging to the plant cadmium resistance (PCR) family, named SaPCR2, from the hyperaccumulating ecotype (HE) of S. alfredii. Sequence analysis indicated that SaPCR2 contained a cysteine-rich domain highly conserved in the PCR family and played an important role in Cd detoxification. Based on the relative quantitative results, SaPCR2 was highly expressed in the roots of HE S. alfredii, but not the shoots and Cd exposure did not significantly affect SaPCR2 expression. In contrast, the expression level of SaPCR2 was very low in plants of its non-hyperaccumulating ecotype (NHE). The subcellular localization of SaPCR2 in tobacco leaves and yeasts showed that SaPCR2 was localized on the plasma membrane and the expression of the SaPCR2 protein in a Zn/Cd-sensitive yeast Δzrc1 significantly increased its tolerance to Cd stress by decreasing the Cd content in cells. Heterologous expression of SaPCR2 in plants of both Arabidopsis thaliana and NHE S. alfredii significantly reduced the Cd levels in the roots, but not in the shoots. These results suggest that the overexpression of SaPCR2 in plants provides a route for Cd leak out of the root cells and protects the root cells against phytotoxicity of Cd stress. To the best of our knowledge, this is the first study of transporter-mediated root efflux of Cd in hyperaccumulator S. alfredii.

Lead (Pb) contamination presents a widespread environmental plague. Sedum alfredii is widely used for soil phytoremediation owing to its capacity to extract heavy metals, such as Pb. Although efficient Pb extraction is mediated by complex interactions between the roots and rhizospheric bacteria, the mechanism by which S. alfredii recruits microorganisms under Pb stress remains unclear. The Pb-accumulating ecotype (AE) and non-accumulating ecotype (NAE) of S. alfredii recruited different rhizobacterial communities. Under Pb stress, AE rhizosphere-enriched bacteria assembled into stable-connected clusters with higher phylogenetic and functional diversity. These microbes, e.g., Flavobacterium, could release indoleacetic acid to promote plant growth and siderophores, thereby increasing Pb availability. The NAE rhizosphere-enriched functional bacteria “desperately” assembled into highly specialized functional clusters with extremely low phylogenetic diversity. These bacteria, e.g., Pseudomonas, could enhance phosphorus solubilization and Pb precipitation, thereby reducing Pb stress and plant Pb accumulation. High niche overlap level of the rhizo-enriched species raised challenges in soil resource utilization, whereas the NAE community assembly was markedly constrained by environmental “selection effect” than that of AE rhizobacterial community. These results indicate that different ecotypes of S. alfredii recruit distinct bacterial functional assemblies to drive specific plant-soil feedbacks for different survival in Pb-contaminated soils. To cope with heavy metal stress, NAE formed a highly functional and specialized but vulnerable community and efficiently blocked heavy metal absorption by plants. However, the AE community adopted a more stable and elegant strategy to promote plant growth and the accumulation of dry matter via multiple evolutionary strategies that ensured a high yield of heavy metal phytoextraction. This for the first time provides new insights into the roles of rhizosphere microbes in plant adaptations to abiotic stresses.

Main conclusion: Cadmium-sensitive yeast screening resulted in the isolation of protein translation factorSaeIF1 from the hyperaccumulatorSedum alfredii which has both general and special regulatory roles in controlling cadmium accumulation. The hyperaccumulator of Sedum alfredii has the extraordinary ability to hyperaccumulate cadmium (Cd) in shoots. To investigate its underlying molecular mechanisms of Cd hyperaccumulation, a cDNA library was generated from leaf tissues of S. alfredii. SaeIF1, belonging to the eukaryotic protein translation factor SUI1 family, was identified by screening Cd-sensitive yeast transformants with this library. The full-length cDNA of SaeIF1 has 582 bp and encodes a predicted protein with 120 amino acids. Transient expression assays showed subcellular localization of SaeIF1 in the cytoplasm. SaeIF1 was constitutively and highly expressed in roots and shoots of the hyperaccumulator of S. alfredii, while its transcript levels showed over 100-fold higher expression in the hyperaccumulator of S. alfredii relative to the tissues of a nonhyperaccumulating ecotype of S. alfredii. However, the overexpression of SaeIF1 in yeast cells increased Cd accumulation, but conferred more Cd sensitivity. Transgenic Arabidopsis thaliana expressing SaeIF1 accumulated more Cd in roots and shoots without changes in the ratio of Cd content in shoots and roots, but were more sensitive to Cd stress than wild type. Both special and general roles of SaeIF1 in Cd uptake, transportation, and detoxification are discussed, and might be responsible for the hyperaccumulation characteristics of S. alfredii. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shenyang Agricultural University is the property of Journal of Shenyang Agricultural University Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hyperaccumulators are the preferred materials for phytoremediation. Sedum alfredii Hance is a cadmium (Cd) hyperaccumulator plant in China, although its detoxification mechanism remains unresolved. In our study, we cloned a gene belonging to the plant cadmium resistance (PCR) family, named SaPCR2 , from the hyperaccumulating ecotype (HE) of S. alfredii. Sequence analysis indicated that SaPCR2 contained a cysteine-rich domain highly conserved in the PCR family and played an important role in Cd detoxification. Based on the relative quantitative results, SaPCR2 was highly expressed in the roots of HE S. alfredii , but not the shoots and Cd exposure did not significantly affect SaPCR2 expression. In contrast, the expression level of SaPCR2 was very low in plants of its non-hyperaccumulating ecotype (NHE). The subcellular localization of SaPCR2 in tobacco leaves and yeasts showed that SaPCR2 was localized on the plasma membrane and the expression of the SaPCR2 protein in a Zn/Cd-sensitive yeast Δ zrc1 significantly increased its tolerance to Cd stress by decreasing the Cd content in cells. Heterologous expression of SaPCR2 in plants of both Arabidopsis thaliana and NHE S. alfredii significantly reduced the Cd levels in the roots, but not in the shoots. These results suggest that the overexpression of SaPCR2 in plants provides a route for Cd leak out of the root cells and protects the root cells against phytotoxicity of Cd stress. To the best of our knowledge, this is the first study of transporter-mediated root efflux of Cd in hyperaccumulator S. alfredii. [ABSTRACT FROM AUTHOR]

Copyright of Forest Research is the property of Forest Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aims: As a vital polysaccharide related to mechanisms of plant resistance to trace metal in the root cell wall, the role of hemicellulose in cadmium (Cd) accumulation in hyperaccumulators is still unknown. We investigated hemicellulose modification in response to Cd in two populations of Sedum alfredii. Methods: Nonhyperaccumulating population (NHP) and hyperaccumulating population (HP) of S. alfredii were grown in nutrient solutions with or without 25 μM Cd for 15 d. Monosaccharide composition of root cell wall hemicellulose and its remolding mechanisms (e.g. enzyme activity and gene expression) were analyzed by using gas chromatography-mass spectrometer (GC-MS), fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance (NMR) and quantitative real-time PCR techniques. Results: In 25 μM Cd treatment, root cell wall hemicellulose in the NHP significantly (P < 0.05) increased and its hemicellulose-bound Cd was nearly 2.5-fold higher than that of HP. In the presence of Cd, xylose and glucose, proved to be the main component of hemicellulose, were higher in the NHP than in the HP owing to the up-regulation of XET/XEH and encoding gene (XTH 31). 113Cd-NMR and FTIR results indicated that hemicellulose with hydroxyl and carboxyl groups of HP retained less Cd than that of NHP. Conclusion: Hemicellulose modification decreased the Cd-binding capacity of the root cell wall and increased the entry of Cd in the shoot of HP S. alfredii. [ABSTRACT FROM AUTHOR]

Sedum alfredii (Crasulaceae) is the only known Cd-hyperaccumulating species that are not in the Brassica family; the mechanism of Cd hyperaccumulation in this plant is, however, little understood. Here, a combination of radioactive techniques, metabolic inhibitors, and fluorescence imaging was used to contrast Cd uptake and translocation between a hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of S. alfredii. The K(m) of (109)Cd influx into roots was similar in both ecotypes, while the V(max) was 2-fold higher in the HE. Significant inhibition of Cd uptake by low temperature or metabolic inhibitors was observed in the HE, whereas the effect was less pronounced in the NHE. (109)Cd influx into roots was also significantly decreased by high Ca in both ecotypes. The rate of root-to-shoot translocation of (109)Cd in the HE was >10 times higher when compared with the NHE, and shoots of the HE accumulated dramatically higher (109)Cd concentrations those of the NHE. The addition of the metabolic inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) resulted in a significant reduction in Cd contents in the shoots of the HE, and in the roots of the NHE. Cd was distributed preferentially to the root cylinder of the HE but not the NHE, and there was a 3-5 times higher Cd concentration in xylem sap of the HE in contrast to the NHE. These results illustrate that a greatly enhanced rate of root-to-shoot translocation, possibly as a result of enhanced xylem loading, rather than differences in the rate of root uptake, was the pivotal process expressed in the Cd hyperaccumulator HE S. alfredii.

The Cd tolerance protein SaCTP3, which responds to Cd stress, was identified in Sedum alfredii ; however, how to improve the efficiency of phytoremediation of Cd–contaminated soil using the CTP gene remains unknown. In this study, the phytoremediation potential of SaCTP3 of Sedum alfredii was identified. In the yeast Cd–sensitive strain Δycf1 overexpressing SaCTP3 , the accumulation of Cd was higher than that in the Δycf1 strain overexpressing an empty vector. Transgenic sorghum plants overexpression SaCTP3 were further constructed to verify the function of SaCTP3. Compared to wild–type plants, the SaCTP3 –overexpressing lines exhibited higher Cd accumulation under 500 μM Cd conditions. The average Cd content in SaCTP3 –overexpressing plants is more than four times higher than that of WT plants. This was accompanied by an enhanced ability to scavenge ROS, as evidenced by the significantly increased activities of peroxidase, catalase, and superoxide dismutase in response to Cd stress. Pot experiments further demonstrated that SaCTP3 overexpression resulted in improved soil Cd scavenging and photosynthetic abilities. After 20 days of growth, the average Cd content in the soil planted with SaCTP3 –overexpressing sorghum decreased by 19.4%, while the residual Cd content in the soil planted with wild–type plants was only reduced by 5.4%. This study elucidated the role of SaCTP3 from S.alfredii , highlighting its potential utility in genetically modifying sorghum for the effective phytoremediation of Cd. [Display omitted] • SaCTP3 overexpression increased Cd accumulation in transgenic sorghum. • Overexpression of SaCTP3 in sorghum increased photosynthesis efficiency. • SaCTP3 –overexpressing sorghum has the potential to effectively remove Cd from the soil. [ABSTRACT FROM AUTHOR]

Background and aims: Sedum alfredii Hance is a hyperaccumulator of cadmium (Cd) and zinc (Zn) that exhibits extraordinary accumulation of these metals in various tissues. The Nicotianamine synthase (NAS) genes play key roles in regulating the production of nicotianamine, a non-protein amino acid that facilitates metal homeostasis in plants, but the functions of these genes in S. alfredii remain unknown. The aims of this study were to identify and characterize the NAS gene from S. alfredii (SaNAS1) and explore NAS roles in Cd or Zn tolerance and accumulation. Methods: One Cd-induced NAS gene from S. alfredii (SaNAS1) was cloned. We determined the subcellular localization of the encoded protein and evaluated SaNAS1 expression. We also assessed SaNAS1 function by conducting a complementary assay with yeast mutants Δzrc1 exposed to Cd or Zn. Finally, transgenic Arabidopsis plants expressing SaNAS1 were produced, and SaNAS1 function was further examined in these plants. Results: SaNAS1 was highly expressed in response to Cd or Zn exposure, and the encoded protein was distributed throughout the cytoplasm and nucleus. Furthermore, yeast expressing SaNAS1 exhibited increased tolerance to Cd or Zn. Finally, expression of SaNAS1 in Arabidopsis increased nicotianamine production and promoted Cd or Zn accumulation in roots and shoots. SaNAS1-expressing transgenic Arabidopsis lines showed improved seedling growth under Cd or Zn stress compared with wild type, indicating that SaNAS1 enhances tolerance to both Cd and Zn. Conclusions: SaNAS1 may play a critical role in Cd or Zn tolerance and hyperaccumulation by regulating nicotianamine level in S. alfredii. [ABSTRACT FROM AUTHOR]

Abstract Phytoextraction is an attractive strategy for remediation of soils contaminated by heavy metal (HM), yet the effects of this practice on biochemical processes involved in soil nutrient cycling remain unknown. Here we investigated the impact of successive phytoextraction with a Cd/Zn co-hyperaccumulator Sedum alfredii (Crassulaceae) on potential nitrification rates (PNRs), abundance and composition of nitrifying communities and functional genes associated with nitrification using archaeal and bacterial 16S rRNA gene profiling and quantitative real-time PCR. The PNRs in rhizosphere were significantly (P < 0.05) lower than in the unplanted soils, and decreased markedly with planting time. The decrease of PNR was more paralleled by changes in numbers of copy and transcript of archaeal amoA gene than the bacterial counterpart. Phylogenetic analysis revealed that phytoextraction induced shifts in community structure of soil group 1.1b lineage-dominated ammonia-oxidizing archaea (AOA), Nitrosospira cluster 3-like ammonia-oxidizing bacteria (AOB) and Nitrospira -like nitrite-oxidizing bacteria (NOB). A strong positive correlation was observed between amoA gene transcript numbers and PNRs, whereas root exudates showed negative effect on PNR. This effect was further corroborated by incubation test with the concentrated root exudates of S. alfredii. Partial least squares path model demonstrated that PNR was predominantly controlled by number of AOA amoA gene transcripts which were strongly influenced by root exudation and HM level in soil. Our result reveals that successive phytoextraction of agricultural soil contaminated by HMs using S. alfredii could inhibit ammonia oxidation and thereby reduce nitrogen loss. Graphical abstract Unlabelled Image Highlights • Successive phytoextraction by S. alfredii significantly reduced the PNR in rhizosphere. • Successive phytoextraction decreased the abundance and activity of archaeal amoA gene. • Successive planting with S. alfredii obviously altered the structure of nitrifying community. • Root exudates of S. alfredii inhibited ammonia oxidation by decreasing ammonia-oxidizing microbe activity. [ABSTRACT FROM AUTHOR]

The Pb-accumulator Sedum alfredii is a good phytoremediation material, and widely used in the phytoremediation research of soils contaminated with Pb. The root exudates from it may be playing a significant role in the process of phytoremediation. In this study, the metabonomics method which based on gas chromatography–mass spectrometry (GC–MS) and pattern recognition analysis was used to identify the remarkable root exudates from S. alfredii under different Pb stresses, including exposure concentrations (0, 10, 50, 200 and 1000 µmol/L) and times (4 and 8 days). And batch extraction experiments were used to verify the roles of these remarkable root exudates. According to the results, 11 metabolites were considered as the remarkable metabolites. Oxalic acid, galactonic acid and glyceric acid can remove Pb in soil, and the removal effect was: oxalic acid > galactonic acid > glyceric acid. Xylose, glucose and maltose have no removal effect for Pb in soil.

Plant uptake of cadmium (Cd) is affected by soil and environmental conditions. In this study, hydroponic experiments were conducted to investigate the effects of elevated CO2 coupled with inoculated endophytic bacteria M002 on morphological properties, gas exchange, photosynthetic pigments, chlorophyll fluorescence, and Cd uptake of S. alfredii. The results showed that bio-fortification processes (elevated CO2 and/or inoculated with endophytic bacteria) significantly (p < 0.05) promoted growth patterns, improved photosynthetic characteristics and increased Cd tolerance of both ecotypes of S. alfredii, as compared to normal conditions. Net photosynthetic rate (Pn) in intact leaves of hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) were increased by 73.93 and 32.90%, respectively at the low Cd (2 μM), 84.41 and 57.65%, respectively at the high Cd level (10 μM). Superposition treatment increased Cd concentration in shoots and roots of HE, by 50.87 and 82.12%, respectively at the low Cd and 46.75 and 88.92%, respectively at the high Cd level. Besides, superposition treatment declined Cd transfer factor of NHE, by 0.85% at non-Cd rate, 17.22% at the low Cd and 22.26% at the high Cd level. These results indicate that elevated CO2 coupled with endophytic bacterial inoculation may effectively improve phytoremediation efficiency of Cd-contaminated soils by hyperaccumulator, and alleviate Cd toxicity to non-hyperaccumulator ecotype of Sedum alfredii. [ABSTRACT FROM AUTHOR]

Abstract Elevated CO 2 and use of endophytic microorganisms have been considered as efficient and novel ways to improve phytoextraction efficiency. However, the interactive effects of elevated CO 2 and endophytes on hyperaccumulator is poorly understood. In this study, a hydroponics experiment was conducted to investigate the combined effect of elevated CO 2 (eCO 2 ) and inoculation with endophyte SaMR12 (ES) on the photosynthetic characteristics and cadmium (Cd) accumulation in hyperaccumulator Sedum alfredii. The results showed that eCO 2 × ES interaction promoted the growth of S. alfredii , shoot and root biomass net increment were increased by 264.7 and 392.3%, respectively, as compared with plants grown in ambient CO 2 (aCO 2 ). The interaction of eCO 2 and ES significantly ( P < 0.05) increased chlorophyll content (53.2%), Pn (111.6%), Pn max (59.8%), AQY (65.1%), and Lsp (28.8%), but reduced Gs, Tr, Rd, and Lcp. Increased photosynthetic efficiency was associated with higher activities of rubisco, Ca2+-ATPase, and Mg2+-ATPase, and linked with over-expression of two photosystem related genes (SaPsbS and SaLhcb2). PS II activities were significantly ( P < 0.05) enhanced with Fv/Fm and Φ(II) increased by 12.3 and 13.0%, respectively, compared with plants grown in aCO 2. In addition, the net uptake of Cd in the shoot and root tissue of S. alfredii grown in eCO 2 × ES treatment was increased by 260.7 and 434.9%, respectively, due to increased expression of SaHMA2 and SaCAX2 Cd transporter genes. Our results suggest that eCO 2 × ES can promote the growth of S. alfredii due to increased photosynthetic efficiency, and improve Cd accumulation and showed considerable potential of improving the phytoextraction ability of Cd by S. alfredii. Graphical abstract Unlabelled Image Highlights • Elevated CO 2 improved the colonization of endophytic bacterium SaMR12. • eCO 2 × SaMR12 interaction had positive effects on S. alfredii growth and Cd accumulation. • eCO 2 × SaMR12 interaction increased photosynthetic carbon uptake. • eCO 2 × SaMR12 interaction promoted electron transport and PS II activity. • eCO 2 × SaMR12 interaction upregulated the expressions of heavy metal transporter. [ABSTRACT FROM AUTHOR]

Highlights • Overexpression of Sedum alfredii cinnamyl alcohol dehydrogenase increases the tolerance of cadmium in Arabidopsis. • Transgenic A. thaliana lines overexpressing SaCAD displayed enhanced accumulation of lignin and antioxidant capacity. • SaCAD -overexpressing plants were capable of retaining more Cd in the cell wall in the Cd-supplied growth medium. Abstract Plant cell walls protect plants from heavy metal stress by resistance, transport and the adsorption process. Cell walls are impregnated with lignin, which enables structural integrity, long-distance water transport and protects plants from many types of stress. Cinnamyl alcohol dehydrogenase (CAD) is an essential enzyme that participates in the final step of the phenylpropanoid lignin biosynthetic pathway and plays an important role in the stress resistance process. In this study, we demonstrated that a CAD-encoding gene in the hyper-accumulating Sedum alfredii Hance, SaCAD, is constitutively expressed in all tissues. While the abundance of the SaCAD transcript is affected by cadmium (Cd) stress, it is upregulated in roots, stems and leaves during Cd treatment. Overexpression of SaCAD in transgenic Arabidopsis thaliana significantly increased CAD activities. Compared with the wild type (WT) plants, the Cd concentrations of SaCAD -overexpressing plants increased in the leaves and roots under Cd stress. The increased fixation of Cd to the thickened cell wall in the SaCAD -overexpressing A. thaliana plants resulted in better growth when the plants were grown in Cd stress conditions. In agreement with these data, SaCAD -overexpressing plants exhibited higher Cd tolerance compared to the wild type (WT) with higher chlorophyll and proline (Pro) contents and antioxidant enzyme activity, as well as a lower methane dicarboxylic aldehyde (MDA) content, electric conductivity and reactive oxygen species when exposed to Cd stress due to a lower amount of Cd distributed in the cytoplasm which is the most site of cytosolic metabolism. SaCAD was found to localize to the cytoplasm of tobacco cells. NMT analysis of the root tips from transgenic A. thaliana lines during Cd stress confirmed that SaCAD -overexpressing plants were capable of retaining more Cd in the cell wall in the Cd-supplied growth medium, which provided additional evidence for the potential role of SaCAD in heavy metal ion compartmentation and detoxification. In summary, we concluded that SaCAD performs critical functions in plants: Cd absorption and fixation to lignified cell wall during stress conditions. [ABSTRACT FROM AUTHOR]

Assessing the effects of phytoextraction on soil properties is important for successful implementation of this method. This study was conducted to evaluate the effects of phytoextraction by Sedum alfredii Hance on the availability of metals and improvement of the microbial community (biomass and structure) of a Cd, Zn and Pb contaminated soil. Phytoextraction significantly decreased the acid extractable, Mn/Fe oxide and organic matter bound fractions of Cd and Zn as well as the acid extractable Pb in the rhizosphere soil. Soil microbial biomass, total, bacterial, actinomycete, fungal, AM fungal, and protozoa phospholipid fatty acids (PLFAs) were significantly enhanced. The ratio of fungal to bacterial and gram-positive to gram-negative bacterial PLFAs were significantly changed. Redundancy analysis showed that microbial biomass and specific groups of PLFAs were negatively correlated with available metals while positively correlated with dissolved organic carbon/organic acids. In conclusion, phytoextraction by S. alfredii reduced available metal concentrations and improved soil microbial properties. [ABSTRACT FROM AUTHOR]

The present study demonstrates the development of an Agrobacterium-mediated genetic transformation method for species of the Sedum genus, which includes the Cd/Zn hyperaccumulator Sedum plumbizincicola and the non-hyperaccumulating ecotype of S. alfredii. Multiple shoots were induced from stem nodes of two Sedum plants using Murashige and Skoog (MS) medium containing 0.1 mg/L cytokinin 6-benzyladenine (6-BA) and 1.0 mg/L auxin 1-naphthaleneacetic acid (NAA). The shoot primordia were used as direct targets for Agrobacterium infection. Selection on hygromycin was highly effective in generating Agrobacterium-transformed explants. This callus-free procedure allowed us to obtain transgenic plantlets after rooting hygromycin-resistant shoots on phytohormone-free MS medium containing the antibiotic. The presence and expression of the reporter genes gusA and GFP in transgenic plants were confirmed by a real-time polymerase chain reaction, histochemical GUS assays, and confocal microscopy. This reliable method for genetic transformation of Sedum plants will help us to understand gene functions and the molecular mechanisms underlying Cd hypertolerance and hyperaccumulation in these species.

Superoxide dismutase (SOD) is a very important reactive oxygen species (ROS)-scavenging enzyme. In this study, the functions of a Cu/Zn SOD gene (SaCu/Zn SOD), from Sedum alfredii, a cadmium (Cd)/zinc/lead co-hyperaccumulator of the Crassulaceae, was characterized. The expression of SaCu/Zn SOD was induced by Cd stress. Compared with wild-type (WT) plants, overexpression of SaCu/Zn SOD gene in transgenic Arabidopsis plants enhanced the antioxidative defense capacity, including SOD and peroxidase activities. Additionally, it reduced the damage associated with the overproduction of hydrogen peroxide (H2O2) and superoxide radicals (O2•-). The influence of Cd stress on ion flux across the root surface showed that overexpressing SaCu/Zn SOD in transgenic Arabidopsis plants has greater Cd uptake capacity existed in roots. A co-expression network based on microarray data showed possible oxidative regulation in Arabidopsis after Cd-induced oxidative stress, suggesting that SaCu/Zn SOD may participate in this network and enhance ROS-scavenging capability under Cd stress. Taken together, these results suggest that overexpressing SaCu/Zn SOD increased oxidative stress resistance in transgenic Arabidopsis and provide useful information for understanding the role of SaCu/Zn SOD in response to abiotic stress.

Interactions between roots and microbes affect plant's resistance to abiotic stress. However, the structural and functional variation of root-associated microbiomes and their effects on metal accumulation in hyperaccumulators remain poorly understood. Here, we characterize the root-associated microbiota of a hyperaccumulating (HP) and a non-hyperaccumulating (NHP) genotype of Sedum alfredii by 16S ribosomal RNA gene profiling. We show that distinct microbiomes are observed in four spatially separable compartments: the bulk soil, rhizosphere, rhizoplane, and endosphere. Both the rhizosphere and rhizoplane were preferentially colonized by Proteobacteria, and the endosphere by Actinobacteria. The rhizosphere and endophytic microbiomes were dominated by the family of Sphingomonadaceae and Streptomycetaceae, respectively, which benefited for their survival and adaptation. The bacterial α-diversity decreases along the spatial gradient from the rhizosphere to the endosphere. Soil type and compartment were strongest determinants of root-associated community variation, and host genotype explained a small, but significant amount of variation. The enrichment of Bacteroidetes and depletion of Firmicutes and Planctomycetes in the HP endosphere compared with that of the NHP genotype may affect metal hyperaccumulation. Program PICRUSt predicted moderate functional differences in bacterial consortia across rhizocompartments and soil types. The functional categories involved in membrane transporters (specifically ATP-binding cassette transporters) and energy metabolism were overrepresented in endosphere of HP in comparison with NHP genotypes. Taken together, our study reveals substantial variation in structure and function of microbiomes colonizing different compartments, with the endophytic microbiota potentially playing an important role in heavy metal hyperaccumulation. [ABSTRACT FROM AUTHOR]

The Pb-accumulatorSedum alfrediiis a good phytoremediation material, and widely used in the phytoremediation research of soils contaminated with Pb. The root exudates from it may be playing a significant role in the process of phytoremediation. In this study, the metabonomics method which based on gas chromatography–mass spectrometry (GC–MS) and pattern recognition analysis was used to identify the remarkable root exudates fromS. alfrediiunder different Pb stresses, including exposure concentrations (0, 10, 50, 200 and 1000 µmol/L) and times (4 and 8 days). And batch extraction experiments were used to verify the roles of these remarkable root exudates. According to the results, 11 metabolites were considered as the remarkable metabolites. Oxalic acid, galactonic acid and glyceric acid can remove Pb in soil, and the removal effect was: oxalic acid > galactonic acid > glyceric acid. Xylose, glucose and maltose have no removal effect for Pb in soil. [ABSTRACT FROM PUBLISHER]

The combined use of organic amendment-assisted phytoextraction and electrokinetic remediation to decontaminate Cd-polluted soil was demonstrated in a laboratory-scale experiment. The plant species selected was the hyperaccumulator Sedum alfredii. Prior to the pot experiment, the loamy soil was treated with 15 g kg of pig manure compost, 10 g kg of humic acid, or 5 mmol kg of EDTA, and untreated soil without application of any amendment was the control. Two conditions were applied to each treatment: no voltage (without an electrical field) and a direct current (DC) electrical field (1 V cm with switching polarity every day). Results indicated that Cd concentrations in S. alfredii were significantly ( p < 0.05) increased by application of the electrical field and soil amendments (pig manure compost, humic acid, and EDTA). By switching the polarity of the DC electrical field, significant pH variation from anode to cathode can be avoided, and no significant impact was observed on shoot biomass production. Electrical field application increased DTPA-extractable Cd in soils and the Cd accumulation in shoots by 6.06-15.64 and 24.53-52.31%, respectively. The addition of pig manure compost and humic acid enhanced shoot Cd accumulation by 1.54- to 1.92- and 1.38- to 1.64-fold because of their simultaneous enhancement of Cd concentration in shoots and biomass production. However, no enhancement of Cd accumulation was found in the EDTA treatment, which can be ascribed to the inhibition of plant growth caused by EDTA. In conclusion, pig manure compost or humic acid addition in combination with the application of a switched-polarity DC electrical field could significantly enhance Cd phytoextraction by hyperaccumulator S. alfredii. [ABSTRACT FROM AUTHOR]

Although the significance of apoplasmic barriers in roots with regards to the uptake of toxic elements is generally known, the contribution of apoplasmic bypasses (ABs) to cadmium (Cd) hyperaccumulation is little understood. Here, we employed a combination of stable isotopic tracer techniques, an ABs tracer, hydraulic measurements, suberin lamellae staining, metabolic inhibitors, and antitranspirants to investigate and quantify the impact of the ABs on translocation of Cd to the xylem in roots of a hyperaccumulating (H) ecotype and a non-hyperaccumulating (NH) ecotype of Sedum alfredii. In the H ecotype, the Cd content in the xylem sap was proportional to hydrostatic pressure, which was attributed to pressure-driven flow via the ABs. The contribution of the ABs to Cd transportation to the xylem was dependent on the Cd concentration applied to the H ecotype (up to 37% at the highest concentration used). Cd-treated H ecotype roots showed significantly higher hydraulic conductance compared with the NH ecotype (76 vs 52 × 10-8 m s-1MPa-1), which is in accordance with less extensive suberization due to reduced expression of suberin-related genes. The main entry sites of apoplasmically transported Cd were localized in the root apexes and lateral roots of the H ecotype, where suberin lamellae were not well developed. These findings highlight the significance of the apoplasmic bypass in Cd hyperaccumulation in hyperaccumulating ecotypes of S. alfredii. [ABSTRACT FROM AUTHOR]

Zinc (Zn) and cadmium (Cd) are two closely related chemical elements with very different biological roles in photosynthesis. Zinc plays unique biochemical functions in photosynthesis. Previous studies suggested that in some Zn/Cd hyperaccumulators, many steps in photosynthesis may be Cd tolerant or even Cd stimulated. Using RNA-seq data, we found not only that Cd and Zn both up-regulated the CA1 gene, which encodes a β class carbonic anhydrase (CA) in chloroplasts, but that a large number of other Zn up-regulated genes in the photosynthetic pathway were also significantly up-regulated by Cd in leaves of the Zn/Cd hyperaccumulator Sedum alfredii . These genes also include chloroplast genes involved in transcription and translation (rps18 and rps14), electron transport and ATP synthesis (atpF and ccsA), Photosystem II (PSBI, PSBM, PSBK, PSBZ/YCF9, PSBO-1, PSBQ, LHCB1.1, LHCB1.4, LHCB2.1, LHCB4.3 and LHCB6) and Photosystem I (PSAE-1, PSAF, PSAH2, LHCA1 and LHCA4). Cadmium and Zn also up-regulated the VAR1 gene, which encodes the ATP-dependent zinc metalloprotease FTSH 5 (a member of the FtsH family), and the DAG gene, which influences chloroplast differentiation and plastid development, and the CP29 gene, which supports RNA processing in chloroplasts and has a potential role in signal-dependent co-regulation of chloroplast genes. Further morphological parameters (dry biomass, cross-sectional thickness, chloroplast size, chlorophyll content) and chlorophyll fluorescence parameters confirmed that leaf photosynthesis of S. alfredii responded to Cd much as it did to Zn, which will contribute to our understanding of the positive effects of Zn and Cd on growth of this plant. [ABSTRACT FROM AUTHOR]

Transgenic research was preformed by transferring a cyanobacterial ( Nostoc flagelliforme) iron superoxide dismutase gene ( NfFeSOD) into heavy metal hyperaccumulator Sedum alfredii via Agrobacterium-mediated method. Beyond expectation, NfFeSOD-overexpressing S. alfredii plants exhibited profound impairments, including plant growth retardation, abnormal root architecture, and reduced leaf greenness, photosynthetic efficiency and metal accumulation efficiency. Although transgenic plants appeared physiologically sensitive to high temperature, a higher relative biomass growth was still observed under long-term high temperature and osmotic stresses. Further investigation found that reactive oxygen species (ROS) homeostasis of transgenic plants was significantly affected, being ~50 % reduction of HO level relative to wild-type plants. Gene transcription including ROS responsive genes was overall attenuated in transgenic plants, being more significant at normal temperature than at high temperature. In addition, ascorbate peroxidase (APX) activity was increased nearly twofolds in transgenic plants as compared to wild-type control. It may be inferred that ectopic NfFeSOD overexpression gives rise to a substantial increase of APX activity and leads to a sharp reduction of HO level, thus impairing basal ROS signaling and plant growth. Specific genetic background of S. alfredii may be responsible for this sharp reduction of HO level induced by NfFeSOD overexpression. S. alfredii plant has acclimated to elevated levels of ROS induced by heavy metals in native habitats and should require high ROS levels for basal signaling. We thus suppose that a sustained disturbance of high basal ROS signaling in metal hyperaccumulators may instead incur very sensitive response and thus result in profound growth impairments. [ABSTRACT FROM AUTHOR]