| The rapid development of industrial and agricultural activities in recent years has caused widespread heavy metal pollution problems in China and globally.As a transition metal,copper is necessary in various metabolic processes of prokaryotes and eukaryotes.Copper is toxic to plants and animals at higher concentrations.In addition,copper can accumulate in the human body through the biological chain,causing serious damage to the human body.The repair of copper pollution is imminent.Compared with traditional physical and chemical remediation,phytoremediation has the advantages of simple operation,low cost,large repair volume,good control effect,and low secondary pollution.Among them,as a large-scale emergent plant,Phragmites australis has the characteristics of cold tolerance,drought resistance,and high survival rate.It is a commonly used plant for water environment management and has certain landscape and economic value.Therefore,this research has used bibliometric analysis in the field of phytoremediation of heavy metal pollution,and analyzed the current research directions and research hotspots in this field;used transcriptomics technology to study the tolerance response mechanism of P.australis to copper stress,and explored how P.australis could improve copper uptake and transport factors of efficiency;studied the growth physiological indicators of P.australis under different copper concentrations,the distribution of heavy metals in each component and the transport coefficients.Combining the tolerance mechanism of P.australis under copper stress and the accumulation strategy of P.australis on copper,two exogenous enhancers were selected to enhance the repair of copper pollution in P.australis,in order to find a strengthening method that can improve the tolerance of P.australis to copper and the absorption and transport of copper.The remediation potential of P.australis on copper pollution provides technical support for the application of phytoremediation technology to the remediation of actual copper-contaminated sites.An overview analysis of research on phytoremediation of heavy metal pollution using the method of bibliometric analysis found that: from 1991 to 2020,countries around the world continued to pay more attention to the field of phytoremediation of heavy metal pollution,and the number of publications increased year by year;China was the country with the largest number of publications.The Chinese Academy of Sciences was also the international scientific research institution with the most publications,but China still need to strengthen international exchanges and cooperation;the research hotspots of phytoremediation of heavy metal pollution were mainly: superaccumulative plants,joint remediation,chelating agents,and the mechanism of phytoremediation technology.At each stage,multiple keywords with high emergence intensity appeared,reflecting the broad development prospects of the discipline;phytoremediation technology was constantly improving,from plant extraction and plant fixation to rhizosphere filtration and joint remediation.Using transcriptomics to analyze the tolerance and response mechanisms of P.australis under copper stress,it has found that the main function of P.australis genes was the signal transduction mechanism,post-translational modification,protein conversion,chaperone proteins,carbohydrate metabolism and general function prediction.There were a total of 1886 differentially expressed genes in the P.australis transcriptome under stress.Among them,the expression of ribosomal and molecular chaperone related genes was significantly up-regulated,while the expression of photosynthesis-related genes was significantly down-regulated,indicating that the photosynthesis of P.australis was inhibited under copper stress,and the P.australis could be coping with copper poisoning through molecular chaperones and other methods.In-depth analysis of photosynthesis with significant differences under copper stress revealed that copper stress inhibited the reaction process of photosynthesis by destroying the membrane protein structure of PSI and the stability of PSII and cytochrome b6/f complexes;P.australis through D-mannose/L-galactose pathway promotes the synthesis of ascorbic acid,which could resist the oxidative stress caused by copper toxicity by accumulating ascorbic acid.The accumulation of proline was synthesized through the ornithine synthesis pathway,rather than the glutamate pathway.As an osmotic regulator,proline could maintain cell homeostasis and remove reactive oxygen species.In the heat shock family under copper stress,there were 20 significantly different genes related to ATP binding,and two differentially expressed genes were related to photosynthesis.The up-regulation of HSP21 expression could protect photosystem II by maintaining the function of P.australis chloroplasts,and it could also directly bind D1 and D2 proteins to protect the core subunits of photosystem II.When photosynthesis was obviously inhibited by copper,the antioxidant system,osmotic adjustment system,and heat shock protein family of P.australis were actively responding to copper poisoning and protecting photosynthesis.Analyzing the growth physiological indexed of P.australis under copper stress,it was found that low-concentration copper stress did not significantly damage the growth parameters of P.australis,while the physiological parameters of P.australis was more sensitive to high-concentration copper stress: with the increase of copper concentration,the chlorophyll content first increased and then decreased.Compared with the control,when the copper stress concentration was 5.0 mg/L,the content of chlorophyll a and chlorophyll b decreased by 21.2% and 23.1%,respectively.At the same time,the cell membrane structure of the leaves was also severely damaged,resulting in increased cell membrane permeability.In addition,the content of ascorbic acid and proline in P.australis leaves gradually increased.When the copper stress was 10 mg/L,they increased by 255.76% and 68.2%,respectively.Plants could reduce the toxic effect of copper on plants by increasing the content of ascorbic acid and proline,and improve the tolerance to heavy metal copper.It can be seen from the content of copper in the various components of the P.australis and the transport factors that a large amount of copper in the P.australis is retained in the underground part under copper stress,and the P.australis can resist copper stress by restricting the migration of copper from the root to other parts and improve the plant resistance to copper.Combining the tolerance mechanism of P.australis under copper stress and the accumulation strategy of P.australis on copper,in order to improve the remediation efficiency of P.australis on copper pollution,the chelating agent EDTA and gas molecule NO were selected to strengthen: the application of the exogenous chelating agent EDTA could promote the growth of the above-ground part of the P.australis and increase the biomass of the P.australis.It could alleviate the effects of copper poisoning on photosynthesis,change the permeability of cell membranes,improve the tolerance of P.australis to copper,and effectively alleviate the inhibitory effect of copper stress on P.australis.In addition,the application of EDTA improved the ability of copper ions to penetrate the roots of the P.australis,and promoted the absorption of more copper ions by the P.australis.The absorption capacity of the P.australis for copper has been significantly improved.And as the concentration of EDTA increased,the transport coefficient of copper also gradually increased,reaching a maximum when the concentration of EDTA was 8 mmol/L,which accelerated the migration rate of heavy metal copper from the underground part of the plant to the above-ground part.The application of exogenous SNP did not significantly improve the tolerance of P.australis to copper stress.The significant increasing in ascorbic acid content indicated that the application of SNP could promote the synthesis of ascorbic acid to eliminate excess ROS in cells and alleviate the oxidative stress caused by heavy metal copper.Compared with the gas molecule NO,the chelating agent EDTA was used to strengthen the remediation efficiency of copper pollution,and the absorption and transport efficiency of copper by the P.australis has been significantly improved. |
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