Soil Microbial Characteristics Under Long-Term Heavy Metal Stress:A Case Study in Zhangshi Wastewater Irrigation Area,Shenyang

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City,China,an area with a 30-year irrigation history with heavy metal-containing wastewater.The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress.In light of the National Environmental Quality Standards of China,the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu,even though wastewater irrigation ceased in 1993.Soil metabolic quotient (qCO_2) had a significant positive correlation,while soil microbial quotient (qM) had a negative correlation with content of soil heavy metals.Soil microbial biomass carbon (MBC) had significantly negative correlation with Cd,but soil substrate-induced respiration (SIR),dehydrogenase activity (DHA),cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content.Soil nutrients,except for phosphorous,showed positive effects on soil microbial characteristics,which to a certain degree obscured the adverse effects of soil heavy metals.Soil Cd contributed more to the soil microbial characteristics,but qM and qCO_2 were more sensitive and showed persistent responses to heavy metals stress.It could be concluded that qM and qCO_2 can be used as bioindicators of heavy metal pollution in soils.

Brassinosteroids and Plant Responses to Heavy Metal Stress. An Overview

Soil contamination with heavy metals has become a world-wide problem, leading to the loss in agricultural productivity. Plants have a remarkable ability to take up and accumulate heavy metals from their external environment and it is well known that high levels of heavy metals affect different physiological and metabolic processes. Brassinosteroids are considered as the sixth class of plant hormones and they are essential for plant growth and development. These compounds are able of inducing abiotic stress tolerance in plants. In this paper, information about brassinosteroids and plant responses to heavy metal stress is reviewed.

Influence of heavy metal stress on morphology and physiology of Penicillium chrysogenum during bioleaching process

In order to improve the efficiency of bioleaching heavy metal from the contaminated soil using Penicillium chrysogenum(P.chrysogenum),experiment was conducted to evaluate the influence of heavy metal stress on P.chrysogenum during bioleaching.The morphology and physiology of P.chrysogenum were observed.Assuming that the heavy metals are all leached out from the experiment soil,heavy metals are added into the agar medium by simulating the heavy metal content in the soil.It is concluded that the survivable heavy metal contaminated soil mass range for P.chrysogenum is 2.5-5.0 g.As for biomass determination,the contaminated soil is added into the liquid medium directly.The soil mass that P.chrysogenum can be survivable is in the range of 2.5-8.75 g.In this mass range,the biomass of P.chrysogenum is bigger than that of the control sample.10 g soil mass is the threshold of the growth of P.chrysogenum.102.2 mg/L gluconic acid,156.4 mg/L oxalic acid,191.6 mg/L pyruvic acid,0.02 mg/L citric acid,0.03 mg/L malic acid and 70.6 mg/L succinic acid are determined after 15 d bioleaching.The mycelium is broken into fragments,and heavy metals are adsorbed on the cell wall or transported into the cytoplasm during bioleaching.The GOD activity declines from 1.08 U/mL to 0.2 U/mL under 400 mg/L of multi-metal stress.The influence of Pb on GOD activity is bigger than that of Cr and Cd,and the GOD activity is not influenced apparently by Mn,Zn and Cu.

Effect of Heavy Metal Stress on Seed Germination of Albizia julibrissin

[Objectives]This study was conducted to investigate the effects of different heavy metal stresses on seed germination,in order to provide a theoretical basis for phytoremediation of soil heavy metal pollution.[Methods]With the seeds of A.julibrissin as an experimental material,the germination test of A.julibrissin seeds under different concentrations of Cu^(2+),Zn^(2+) and Pb^(2+) was carried out.The germination potential,germination rate,germination index,radicle length,embryo length and other indexes were measured.[Results]①Different heavy metals had different effects on the germination of A.julibrissin seeds.Low concentrations of Cu^(2+),Zn^(2+) and Pb^(2+) stresses had certain promotion effects on the germination of A.julibrissin seeds,but high concentrations of Cu^(2+),Zn^(2+),Pb^(2+) stresses had obvious inhibitory effects on the germination of A.julibrissin seeds.②There were obvious differences in the tolerance of A.julibrissin seeds to different metal ion stresses.According to the comparison of the average values of membership functions,the order of their tolerance to different heavy metal ions was:Zn^(2+)>Cu^(2+)>Pb^(2+).[Conclusions]In the case of light pollution,the germination of A.julibrissin seeds was not inhibited,and the use of this plant for the remediation of lightly contaminated soil with heavy metals can also be considered.

Accumulation behavior of heavy metals by Bidens pilosa L.from metallurgical slag:effects on plant physiology and absorption characteristics

Many of the abandoned mining and industrial land in villages and towns are seriously polluted by heavy metals in China,it is necessary for sustainable development to adopt efficient and economical ways to restore the ecology of abandoned mining and industrial land.Pollution level of topsoil contaminated with metallurgical slag from nonferrous metal smelting waste site in Baoding,North China and the heavy metals(HMs)accumulation behavior of Bidens pilosa L.(B.pilosa,native pioneer plant)were studied.Two selected study sites were mainly contaminated by As(270~434 mg/kg),Cd(63~95 mg/kg),Pb(5496~24504 mg/kg)and Zn(4500~21300 mg/kg),which exceed the national standard severely.Investigation of multi-metal accumulation in different parts of B.pilosa indicated that the absorption of toxic metals varied by types,concentration and species of HMs under stress conditions,soil property and plant tissues.The results showed that B.pilosa had excellent ability to accumulate HMs under different HMs stress condition,with the highest accumulation concentration of 85 mg/kg for As,380 mg/kg for Cd,4000 mg/kg for Pb,and 7500 mg/kg for Zn in roots under experimental conditions,respectively.The growth trend of B.pilosa declined with the increase of HMs stress concentration in tested soils.HMs stress led to different degrees of plant toxicity and obstruction of physiological metabolism.Among the plant physiological index,Chla and ChlT decreased 28.0%and 28.1%,37.3%and 35.5%under different stress treatments,respectively.Indicators related to physiological metabolic strength and stress resistance of plant,such as MDA(Malondiadehyde),CAT(catalase),SOD(superoxide dismutase)and SP(soluble protein),all increased with the increase of HMs stress concentration.

Cd and Hg Mediated Oxidative Stress,Antioxidative Metabolism and Molecular Changes in Soybean(Glycine max L.)

Cadmium(Cd)and Mercury(Hg)is among the heavy metals most hazardous for plant and human health.Known to induce oxidative stress in plants and disbalance equilibrium in the antioxidant defence system,these metals alter plant growth and cause damage at the cellular and molecular levels.Soybean is an important oilseed crop that is raised in soils often contaminated by Cd and Hg.The comparative studies on the deleterious effect of Cd and Hg and the defence system of antioxidants were not studied earlier in soybean plant.In this study,soybean plants were exposed to Cd(100μM CdCl_(2))and Hg(100μM HgCl_(2))and studied for physiological,biochemical and molecular responses.Both Cd and Hg treatment increased the magnitude of oxidative stress.Activities of antioxidant enzymes were significantly upregulated in response to Cd and Hg stress.Quantitative and qualitative assessment of isolated RNA showed significant differences in RNA under stress.Integrity values of RNA confirmed alterations.Transcript level of the Actin gene,involved in the morphogenesis of plants and also used as referenced gene in expression studies was analyzed using qRT-PCR just to check its stability and response under heavy metal stress.Results showed significant upregulation of the gene in the presence of Cd.It can be concluded that both Cd and Hg caused oxidative damage to plants,and adversely affected the quality of RNA.However,soybean tried to limit the adverse impacts of Cd and Hg stress by elevating the antioxidant system and upregulating Actin gene.

Comparative study of responses in the brown algae Sargassum thunbergii to zinc and cadmium stress

Heavy metal pollution in aquatic system is becoming a serious problem worldwide. In this study, responses of Sargassum thunbergii to dif ferent concentrations(0, 0.1, 0.5, 1.0 and 5.0 mg/L) of zinc(Zn) and cadmium(Cd) exposure separately were studied for 15 days in laboratory-controlled conditions. The results show that the specifi c growth rates increased slightly under the lower Zn concentration treatment(0.1 mg/L) at the first 5 d and then decreased gradually, which were significantly reduced with the exposure time in higher Zn concentrations and all Cd treatments compared to respective control, especially for 1.0 and 5.0 mg/L Cd. Chlorophyll a contents showed significant increase in 0.1 mg/L Zn treatment, whereas the gradually reduction were observed in the other three Zn treatments and all Cd treatments. The oxygen evolution rate and respiration rate presented distinct behavior in the Zn-treated samples, but both declined steadily with the exposure time in Cd treatments. The P/R value analyses showed similar variation patterns as chlorophyll a contents. Real-time PCR showed that lower Zn concentration(0.1 mg/L) increased mRNA expression of rbcL gene, whereas higher Zn concentrations and Cd reduced the rbcL expression. Taken together, these findings strongly indicate that Zn and Cd had different effects on S. thunbergii both at the physiological and gene transcription levels, the transcript level of photosynthesis-related gene rbcL can be used as an useful molecular marker of algal growth and environment impacts.

Advances in Research on Effect of Heavy Metals Cd and Pb on Wheat and Mitigation Effect of Conditioners

In this article,the effect of heavy metals Cd and Pb on seed germination,seedling growth and yield of wheat is investigated,and the effect of related conditioners on improving soil and alleviating Cd and Pb stress is explored.

Genomics,transcriptomics,and peptidomics of the greater wax moth Galleria mellonella neuropeptides and their expression in response to lead stress

Neuropeptides are crucial in regulation of a rich variety of developmental,physiological,and behavioral functions throughout the life cycle of insects.Using an integrated approach of multiomics,we identified neuropeptide precursors in the greater wax moth Galleria mellonella,which is a harmful pest of honeybee hives with a worldwide distribution.Here,a total of 63 and 67 neuropeptide precursors were predicted and annotated in the G.mellonella genome and transcriptome,in which 40 neuropeptide precursors were confirmed in the G.mellonella peptidome.Interestingly,we identified 12 neuropeptide precursor genes present in G.mellonella but absent in honeybees,which may be potential novel pesticide target sites.Honeybee hives were contaminated with heavy metals such as lead,enabling its bioaccumulation in G.mellonella bodies through the food chain,we performed transcriptome sequencing to analyze the effects of Pb stress on the mRNA expression level of G.mellonella neuropeptide precursors.After treatment by Pb,the expression of neuropeptide F1 was found to be significantly downregulated,implying that this neuropeptide might be associated with responding to the heavy metal stress in G.mellonella.This study comprehensively identified neuropeptide precursors in G.mellonella,and discussed the effects of heavy metals on insect neuropeptides,with the example of G.mellonella.The results are valuable for future elucidation of how neuropeptides regulate physiological functions in G.mellonella and contribute to our understanding of the insect's environmental plasticity and identify potential new biomarkers to assess heavy metal toxicity in insects.

Research Progress of Maternal Environmental Effects in Resource-based Regions

Heavy metal pollution is common in resource-based regions.However,the morphological,physiological and biochemical mechanisms of plants transmitting environmental information to their offspring in environments polluted by heavy metals have not been studied yet.Taking soybean,an annual self-pollinated plant in Huang-Huai-Hai region,as the research object,the morphological,physiological and biochemical indexes and heavy metal enrichment and distribution characteristics of plants under heavy metal stress were monitored continuously for about three generations,and the trans-generational differences of soybean reproduction,vegetative growth,stress resistance and life cycle in heavy metal stress environment were elucidated.The results will be helpful to better understand the long-term adaptive strategy of plants to heavy metal stress and provide the theory basis for ecological security of soybean and other crops under heavy metal stress.

Application of semi-analytical finite element method to analyze asphalt pavement response under heavy traffic loads

Accurate assessment of the impact of heavy traffic loads on asphalt pavements requires a computational model which is able to calculate the response of the pavement fast and precisely. Currently the most finite element analysis programs based on traditional methods have various limitations. A specific program SAFEM was developed based on a semi-analytical finite element method to overcome the problems. It is a three-dimensional FE program that requires only a two-dimensional mesh by incorporating the semi- analytical method using Fourier series in the third dimension. The computational accuracy and efficiency of the program was verified by analytical verification previously. The experimental verification is carried out in this paper and the results show that the SAFEM is able to predict the mechanical responses of the asphalt pavement. Using the program SAFEM, the impact of heavy traffic loads was analyzed in terms of stress and strain dis- tribution, surface deflection and fatigue life. The results indicate that if the asphalt pave- ment is subjected to the heavy traffic load more, the thicknesses and stiffness of the pavement structural layers should be increased adequately in order to support the surface deflection, The compressive stress in asphalt binder course is relatively large and increases more significantly compared with that in the other asphalt layers when the axle load becomes larger. With comparison of the predicted fatigue life, the increase of the axle load will lead to the destruction of the asphalt pavement extremely easily.

Transcription factor OsWRKY72 is involved in Cu/Cd toxicity by regulating lignin synthesis in rice

Maintenance of ion homeostasis in plant cells is an essential physiological requirement for sustainable growth,development,and yield of crops.Plants respond to high levels of heavy metals such as copper(Cu)and cadmium(Cd)to avoid irreversible damage at the structural,physiological and molecular levels.Our previous study found that rice germin-like proteins(OsGLPs)are a type of Cu-responsive proteins.The deletion of 10 tandem OsGLP genes on chromosome 8 led to more severe heavy metal toxicity in rice.In this study,we show that rice WRKY transcription factor OsWRKY72 negatively regulates OsGLP8-7transcription.Overexpression of OsWRKY72 weakens the Cu/Cd tolerance of rice when exposed to Cu and Cd.OsWRKY72 suppressed expression of OsGLP8-7 and lignin synthesis genes,resulting in reduced lignin polymerization and consequently lower lignin accumulation in cell walls,thereby increasing the Cu and Cd accumulation.In addition,OsWRKY53 bound to OsWRKY72 to alleviate the transcriptional inhibition of OsGLP8-7.These results revealed that OsWRKY72-OsGLP8-7 is an important module response of rice to heavy metal stress,and that transcription factor OsWRKY72 acts upstream of OsGLP8-7 to regulate Cu/Cd toxicity.

Effect of Dark Septate Endophytic Fungus Gaeumannomyces cylindrosporus on Plant Growth, Photosynthesis and Pb Tolerance of Maize (Zea mays L.)

Dark septate endophytic （DSE） fungi are ubiquitous and cosmopolitan, and occur widely in association with plants in heavy metal stress environment. However, little is known about the effect of inoculation with DSE fungi on the host plant under heavy metal stress. In this study, Gaeumannomyces cylindrosporus, which was isolated from Pb-Zn mine railings in China and had been proven to have high Pb tolerance, was inoculated onto the roots of maize （Zea mays L.） seedlings to study the effect of DSE on plant growth, photosynthesis, and the translocation and accumulation of Pb in plant under stress of different Pb concentrations. The growth indicators （height, basal diameter, root length, and biomass） of maize were detected. Chlorophyll content, photosynthetic characteristics （net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO2 concentration）, and chlorophyll fluorescence parameters in leaves of the inoculated and non-inoculated maize were also determined. Inoculation with G. cylindrosporus significantly increased height, basal diameter, root length, and biomass of maize seedlings under Pb stress. Colonization of G. cylindrosporus improved the efficiency of photosynthesis and altered the translocation and accumulation of Pb in the plants. Although inoculation with G. cylindrosporus increased Pb accumulation in host plants in comparison to non-inoculated plants, the translocation factor of Pb in plant body was significantly decreased. The results indicated that Pb was accumulated mainly in the root system of maize and the phytotoxicity of Pb to the aerial part of the plant was alleviated. The improvement of efficiency of photosynthesis and the decrease of translocation factor of Pb, caused by DSE fungal colonization, were efficient strategies to improve Pb tolerance of host plants.

Phyto-Toxicity of Chromium in Maize： Oxidative Damage, Osmolyte Accumulation, Anti-Oxidative Defense and Chromium Uptake

Agricultural production systems are immensely exposed to different environmental stresses in which heavy metal stress receives serious concerns. This study was conducted to explore the deleterious effects of different chromium （Cr） stress levels, i.e., O, 30, 60, 90, 120, and 150 μmol L^-1, on two maize genotypes, Wandan 13 and Runnong 35. Both genotypes were evaluated by measuring their growth and yield characteristics, Cr accumulation in different plant tissues, alterations in osmolyte accumulation, generation of reactive oxygen species （ROS）, and anti-oxidative enzyme activity to scavenge ROS. The results showed that Cr stress decreased the leaf area, cob formation, 100-grain weight, shoot fresh biomass, and yield formation, while Cr accumulation in different maize tissues was found in the order of roots 〉 leaves 〉 stem ~ seeds in both genotypes. The increased Cr toxicity resulted in higher free proline, soluble sugars and total phenolic contents, and lower soluble protein contents. However, enhanced lipid peroxidation was noticed in the forms of malondialdehyde, hydrogen peroxide （H2O2） and thiobarbituric acid reactive substance accumulation, and electrolyte leakage. The hyperactivity of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, especially glutathione peroxidase and glutathione reductase indicated that these anti-oxidative enzymes had a central role in protecting maize from Cr toxicity, especially for Wandan 13. Moreover, higher uptake and less translocation of Cr contents into the grains of Wandan 13 implied its importance as a potential candidate against soil Cr pollution.

Effects of Cadmium on Polar Lipid Composition and Unsaturation in Maize(Zea mays) in Hydroponic Culture

This study aimed to evaluate the effect of Cd exposure （100 μmol/L） on polar lipid composition, and to examine the level of fatty acid unsaturation in maize （Zea mays L.）. In roots, the level of 16：0 and monounsaturated fatty acids （16：1 ＋ 18：1） decreased in phosphatidylcholine （PC） and phosphatidylethanolamine （PE）. In contrast, the proportion of unsaturated 18-C fatty acid species showed an opposite response to Cd. The content, on the other hand, of PC, PE, digalactosyldiacylglycerol （DGDG）, and steryl lipids increased in roots （2.9-, 1.6-, 5.3-, and 1.7-fold increase, respectively）. These results suggest that a more unsaturated fatty acid composition than found in control plants with a concomitant increase in polar lipids may favor seedling growth during Cd exposure. However, the observed increase in the steryl lipid （SL） ： phospholipid （PL） ratio （twofold）, the decrease in monogalactosyldiacylglycerol （MGDG） ： DGDG ratio, as well as the induction of lipid peroxidation in roots may represent symptoms of membrane injury. In shoots, the unsaturation level was markedly decreased in PC and phosphatidylglycerol （PG） after Cd exposure, but showed a significant increase in sulfoquinovosyldiacylglycerol （SQDG）, MGDG and DGDG. The content of PG and MGDG was decreased by about 65%, while PC accumulated to higher levels （4.4-fold increase）. Taken together, these changes in the polar lipid unsaturation and composition are likely to be due to alterations in the glycerolipid pathway. These results also support the idea that the increase in overall unsaturation plays some role in enabling the plant to withstand the metal exposure.

Mutualistic fungus Piriformospora indica modulates cadmium phytoremediation properties of host plant via concerted action of enzymatic and non-enzymatic biochemicals

Soils and ecosystems contaminated with cadmium (Cd) threaten human health and adversely affect morphological,physiological,and biochemical parameters of plants.The symbiotic association of endophytic fungi with their host plants is the best strategy to improve various plant characteristics and remediate soils polluted with heavy metal(loid)s (HMs).Being a well-known plant growth-promoting fungus,Piriformospora indica confers resistance against a number of abiotic stresses,including HM stress.This pot experiment explored the potential and ameliorative effects of P.indica on Artemisia annua L.plants treated with different concentrations (0,40,80,and 120 mg kg-1) of Cd.Inoculation with P.indica significantly increased plant performance,especially by enhancing chlorophyll concentration and water potential and by decreasing electrolytic leakage,when compared with un-inoculated plants,despite the high Cd levels.Similarly,P.indica enhanced antioxidant enzyme activities,thereby reducing the drastic effects of Cd in inoculated plants.In addition,P.indica accumulated Cd in the roots of colonized plants,as revealed by atomic absorption spectroscopy,and restricted Cd translocation to aerial parts.Furthermore,P.indica showed in vitro resistance (up to a certain level) to Cd stress;however,fungus growth was inhibited at very high Cd concentrations,proving it an excellent candidate for use as a potential phytoremediator in fields affected by Cd contamination.The transcriptional analysis showed that the signaling genes and artemisinin and flavonoid biosynthetic pathway genes were significantly upregulated in P.indica-co-cultivated plants when compared with un-inoculated plants,suggesting a fine collaboration between primary and secondary metabolisms to modulate resistance capacity and to enhance the phytoremediation capability of A.annua against Cd toxicity.