Zinc adsorption and desorption characteristics in root cell wall involving zinc hyperaccumulation in Sedum alfredii Hance

Radiotracer techniques were employed to characterize 65Zn adsorption and desorption in root-cell-wall of hyperac-cumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) species of Sedum alfredii Hance. The results indicated that at the end of a 30 min short time radioisotope loading period, comparable amounts of 65Zn were accumulated in the roots of the two ecotypes Sedum alfredii, whereas 2.1-fold more 65Zn remains in NHE root after 45-min desorption. At the end of 60 min uptake period, no difference of 65Zn accumulation was observed in undesorbed root-cell-wall of Sedum alfredii. However, 3.0-fold more 65Zn accumulated in desorbed root-cell-wall of NHE. Zn2+ binding in root-cell-wall preparations of NHE was greater than that in HE under high Zn2+ concentration. All these results suggested that root-cell-wall of the two ecotypes Sedum alfredii had the same ability to adsorb Zn2+, whereas the desorption characteristics were different, and with most of 65Zn binding on root of HE being available for loading into the xylem, as a result, more 65Zn was translocated to the shoot.

Differential generation of hydrogen peroxide upon exposure to zinc and cadmium in the hyperaccumulating plant specie(Sedum alfredii Hance)

Sedum alfredii Hance has been identified as zinc(Zn) and cadmium(Cd) co-hyperaccumulator.In this paper the relationships of Zn or Cd hyperaccumulation to the generation and the role of H2O2 in Sedum alfredii H.were examined.The results show that Zn and Cd contents in the shoots of Sedum alfredii H.treated with 1000 μmol/L Zn2+ and/or 200 μmol/L Cd2+ increased linearly within 15 d.Contents of total S,glutathione(GSH) and H2O2 in shoots also increased within 15 d,and then decreased.Total S and GSH contents in shoots were higher under Cd2+ treatment than under Zn2+ treatment.However,reverse trends of H2O2 content in shoots were obtained,in which much higher H2O2 content was observed in Zn2+-treated shoots than in Cd2+-treated shoots.Similarly,the microscopic imaging of H2O2 accumulation in leaves using H2O2 probe technique showed that much higher H2O2 accumulation was observed in the Zn2+-treated leaf than in the Cd2+-treated one.These results suggest that there are different responses in the generation of H2O2 upon exposure to Zn2+ and Cd2+ for the hyperaccumulator Sedum alfredii H.And this is the first report that the generation of H2O2 may play an important role in Zn hyperaccumulation in the leaves.Our results also imply that GSH may play an important role in the detoxification of dissociated Zn/Cd and the generation of H2O2.

Integrated Fertilization Regimes Boost Heavy Metals Accumulation and Biomass of Sedum alfredii Hance

The hyperaccumulator Sedum alfredii Hance(S.alfredii)may be employed for zinc(Zn)and cadmium(Cd)-polluted soil remediation.However,the low phytoremediation efficiency,related to the low biomass production,limits its use with that purpose.In this experiment,nitrogen(N),phosphorus(P),and potassium(K)fertilizers,and organic manure were applied to investigate the phytoremediation ability of S.alfredii.Hydroponic and pot experiments were conducted using Zn-Cd polluted soil.The hydroponic experiment indicated that appropriate fertilizer application could increase(p<0.05)the amount of accumulated Zn and Cd in S.alfredii.When N supply ranged from 0.5 to 2.5 mmol L^(−1),it could improve growth and accumulation of Zn and Cd in whole plants of S.alfredii.The 1 mmol L^(−1) N was an optimal N dosage for shoot biomass production and Cd accumulation in shoots,while the 2.5 mmol L^(−1) was an optimal N dosage for Zn accumulation in shoots.Both low(<0.05 mmol L^(−1))and high(>0.8 mmol L^(−1))P supply decreased growth,and Zn/Cd accumulation in whole plants of the studied species.The 0.1 mmol L^(−1) P was an optimal dosage for S.alfredii biomass production and Zn/Cd accumulation in shoots.The supply levels within the range from 0.3 to 1 mmol L^(−1) K could significantly improve the biomass production of S.alfredii and its capability to accumulate Zn and Cd in the biomass.The 0.5 mmol L^(−1) K was an optimal dosage for the whole biomass production and Zn accumulation in shoots,while the 1 mmol L^(−1) was an optimal K dosage for Zn accumulation in shoots,which was 17.2%higher than the control.Moreover,the soil pot experiment showed that the combination of organic(fermented manure)and inorganic fertilizers made significant effects on the Zn and Cd-polluted soil remediation by S.alfredii.These effects varied,however,with the application of different proportions of N,P,K and organic matter.The Zn accumulation by S.alfredii reached the highest efficiency ability under the highest fertilizer mixing rate(N:50 mg kg^(−1),P:40 mg kg^(−1),K:100 mg kg^(−1),organic matter:1%).Even more,S.alfredii showed the strongest ability to accumulate Cd with a lower fertilizer mixing rate(N:25mg kg^(−1),P:20mg kg^(−1),K:50 mg kg^(−1),organic matter:0.5%).

Organic Materials Could Improve the Phytoremediation Efficiency of Soil Potentially Hazardous Metal by Sedum alfredii Hance

Soil potentially hazardous metal(PHM)is continually attracting public attention worldwide,due to its highly toxic properties and potentially huge damage to human being through food chain.Phytoremediation is an effective and eco-friendly way in remediation technology.A pot experiment was carried out to investigate the effect of different organic materials(biogas residue(BR),mushroom residue(MR),and bamboo-shoot shell(BS))application on phytoremediation of two PHM-contaminated soils(Fuyang soil as‘heavily-polluted soil’and Wenzhou soil as‘moderately-polluted soil’,respectively)by Sedum alfrecdii Hance.The results indicated:1)for moderately-polluted soil,the 5%BR treatment had the strongest activation to Cu and Zn,for heavily-polluted soil,1%BS treatment had the highest activation effect for Cu,Zn,Pb and Cd.2)the above-ground biomass of Sedum alfredii Hance increased with the addition rate of organic materials.3)for Cd uptake of Sedum alfredii Hance in moderately-polluted soil,only 1%BS treatment had a better accumulation effect,compared to the control,for Zn element,MR treatments were weaker than the control,while other treatments were better than the control,of which 5%BR,1%BS and 5%BS accumulated more Zn element by 39.6%,32.6%and 23.8%,respectively;in heavily-polluted soil,the treatments of 5%BS,1%BR and 5%BR accumulated more Cd than the control by 12.9%,12.8%and 6.2%,respectively,the treatments with organic materials addition promoted Zn accumulation in shoots of Sedum alfredii Hance,and the best treatment was 5%BS.Therefore,an appropriate application rate of BS and BR could improve the remediation efficiency for Zn/Cd contaminated soils by Sedum alfredii Hance.

Combined remediation of DDT congeners and cadmium in soil by Sphingobacterium sp.D-6 and Sedum alfredii Hance

Combined pollution of 1,1,1-trichloro-2,2-bis （4-chlorophenyl） ethane （DDT） and cadmium （Cd） in agricultural soils is of great concern because they present serious risk to food security and human health.In order to develop a cost-effective and safe method for the removal of DDTs and Cd in soil,combined remediation of DDTs and Cd in soil by Sphingobacterium sp.D-6 and the hyperaccumulator,Sedum alfredii Hance was investigated.After treatment for 210 days,the degradation half-lives of DDTs in soils treated by strain D-6 decreased by 8.1% to 68.0% compared with those in the controls.The inoculation of strain D-6 into soil decreased the uptake of DDTs by pak choi and S.alfredii.The shoots/roots ratios of S.alfredii for the Cd accumulation ranged from 12.32 to 21.75.The Cd concentration in soil decreased to 65.8%-71.8% for S.alfredii treatment and 14.1%-58.2% for S.alfredii and strain D-6 combined treatment,respectively,compared with that in the control.The population size of the DDTs-degrading strain,Simpson index （1/D） and soil respiratory rate decreased in the early stage of treatment and then gradually increased,ultimately recovering to or exceeding the initial level.The results indicated that synchronous incorporation of strain D-6 and S.alfredii into soil was found to significantly （p 0.05） enhance the degradation of DDTs in soil and the hyperaccumulation of Cd in S.alfredii.It was concluded that strain D-6 and S.alfredii could be used successfully to control DDTs and Cd in contaminated soil.

Chromosome doubling of Sedum alfredii Hance: A novel approach for improving phytoremediation efficiency

Sedum alfredii Hance is a cadmium(Cd)/zinc(Zn)hyperaccumulator native to China.However,its relatively low biomass restricted the large-scale application for heavy metal contamination remediation.The chromosome set doubling of S.alfredii in vitro was achieved by 0.1%–0.2%(W/V)colchicine treatment.The plant DNA ploidy was analyzed by flow cytometry and chromosome set doubling plants(CSD)were identified based on the obvious different sharp peak.A tissue culture experiment with different Cd treated levels and a field trial with natural polluted mined soil were conducted to study the effects of chromosome doubling on plant biomass and Cd accumulation in shoots.The results suggested that S.alfredii is a mixoploid.Compared with the wild type plants(WT),CSD exhibited typical"gigas"characteristics in morphology including stem thickness,root hair production,number of leaves and size of stoma guard cell.Fresh weight and dry weight of CSD were increased to 1.62–2.03-fold and 2.26–3.25-fold of WT.And Cd content of CSD showed a17.49%–42.82%increase and 59%increase under tissue culture and field condition,accordingly.In addition,the TF and in BCF of CSD were 2.37-and 1.59-fold of WT,respectively.These results proved that it is feasible to promote phytoextraction efficiency of S.alfredii in Cd contaminated soils through chromosomal engineering,which provides a novel approach for hyperaccumulator application in phytoremediation.

Response of ATP sulfurylase and serine acetyltransferase towards cadmium in hyperaccumulator Sedum alfredii Hance

We studied the responses of the activities of adenosine-triphosphate (ATP) sulfurylase (ATPS) and serine acetyltransferase (SAT) to cadmium (Cd) levels and treatment time in hyperaccumulating ecotype (HE) Sedum alfredii Hance, as compared with its non-hyperaccumulating ecotype (NHE). The results show that plant growth was inhibited in NHE but promoted in HE when exposed to high Cd level. Cd concentrations in leaves and shoots rapidly increased in HE rather than in NHE, and they became much higher in HE than in NHE along with increasing treatment time and Cd supply levels. ATPS activity was higher in HE than in NHE in all Cd treatments, and increased with increasing Cd supply levels in both HE and NHE when exposed to Cd treatment within 8 h. However, a marked difference of ATPS activity between HE and NHE was found with Cd treatment for 168 h, where ATPS activity increased in HE but decreased in NHE. Similarly, SAT activity was higher in HE than in NHE at all Cd treatments, but was more sensitive in NHE than in HE. Both ATPS and SAT activities in NHE leaves tended to decrease with increasing treatment time after 8 h at all Cd levels. The results reveal the different responses in sulfur assimilation enzymes and Cd accumulation between HE and NHE. With increasing Cd stress, the activities of sulfur assimilation enzymes (ATPS and SAT) were induced in HE, which may contribute to Cd accumulation in the hyperaccumulator Sedum alfredii Hance.

Extraction and isolation of the salidroside-type metabolite from zinc(Zn) and cadmium(Cd) hyperaccumulator Sedum alfredii Hance

The active metabolite in the post-harvested biomass of zinc(Zn) and cadmium(Cd) hyperaccumulator Sedum alfredii Hance from phytoextraction is of great interest in China.The current study demonstrates that a salidroside-type metabolite can be yielded from the Zn/Cd hyperaccumulator S.alfredii biomass by means of sonication/ethanol extraction and macroporous resin column(AB-8 type) isolation.The concentrations of Zn and Cd in the salidroside-type metabolite were below the limitation of the national standards.

Remediation mechanism of“double-resistant”bacteria—Sedum alfredii Hance on Pb-and Cd-contaminated soil

Background:Concentrations of heavy metals continue to increase in soil environments as a result of both anthro-pogenic activities and natural processes.Cadmium(Cd)and lead(Pb)is one of the most toxic heavy metals and pose health risks to both humans and the ecosystem.Therefore,effectively solving the problem of heavy metal pollution is the concern of soil workers.Among the existing remediation techniques,only the combined use of microorganisms and plants for remediation of heavy metal-contaminated soil is the greenest and most developed one.Consequently,based on this background,this study investigates the remediation mechanism of Pb and Cd heavy metals using the combined action of bacteria and Sedum alfredii Hance.Methods:In order to enrich the research theory of combined plant and microorganism remediation of heavy metal-contaminated soil,we constructed a heavy metal composite pollution remediation system by combining Pb and Cd-tolerant bacteria with the Pb and Cd hyperaccumulator plant—Sedum alfredii Hance to investigate its combined remediation effect on Pb and Cd composite contaminated soil.Results:The results showed that resistant bacteria were able to promote enrichment of Pb and Cd in Sedum alfredii Hance and J2(200 ml of bacterial solution)was significantly(P<0.05)more effective than J1(100 ml of bacterial solution).The resistant bacteria were able to alleviate the toxic effects of Pb and Cd heavy metals on Sedum alfredii Hance and promote growth while reducing rhizosphere soil pH.The resistant bacteria were able to significantly reduce the effective state of Pb and Cd in the rhizosphere soil(P<0.05),with the greatest reduction in the effective state of Pb in treatment A(Cd7Pb100 mg/kg),where J2 was reduced by 9.98%compared to J0,and the greatest reduction in the effective state of Cd in treatment C(Cd28Pb400 mg/kg),where J2 was 43.53%lower than J0.In addition,the resistant bacteria were able to increase the exchangeable state Cd content by 0.97 to 9.85%.The resistant bacteria had a weakly promoting effect and a highly inhibitory effect on the absorption of Pb by Sedum alfredii Hance.Conclusions:The resistant bacteria can change the rhizosphere environment and significantly improve the remedia-tion effect of Sedum alfredii Hance on heavy metal cadmium.The role of“double-resistant”bacteria in promoting the accumulation of Cd was greater than that of Pb.

Zn Accumulation and Subcellular Distribution in the Zn Hyperaccumulator Sedurn alfredii Hance

Zn accumulation and subcellular distribution in leaves of the hyperaccumulating ecotype （HE） and non-hyperaccumulating ecotype （NHE） of Sedum alfredii Hance were studied using radiotracer and gradient centrifugation techniques. Leaf Zn accumulation in the HE of S. alfredii was 18.5-26.7 times greater than that in the NHE when the plants were grown at 1-500μmol Zn L-1. Leaf section uptake of 65Zn was highly dependent on external Zn levels. Greater 65Zn uptake in HE was noted only at external Zn levels 〉 100μmol L-1. Zinc subcellular distribution in the leaves of the two ecotypes of S. alfredii was： cell wall 〉 soluble fraction 〉 cell organelle. However, more Zn was distributed to the leaf cell wall and soluble fractions for HE than for NHE. In the leaf of HE, 91%-94% of the Zn was found in the cell walls and the soluble fraction and only 6%-9% Zn was distributed in the cell organelle fraction. For NHE, about 20%-26% Zn was recovered in the cell organelle fraction. In stems, Zn distribution to the ceil wail fraction was approximately two fold greater in the HE than that in the NHE. For the hyperaccumulating ecotype of S. alfredii, the cell wall and the vacuole played a very important role in Zn tolerance and hyperaccumulation.