Effects Of Cadmium And Lead Combination On Growth Characteristics In Medicinal Plant Of Lingusticum Chuanxiong Hort.

As the main polluted heavy metals in agricultural ecosystem,cadmium（Cd）and lead（Pb）combined pollution often exists in soil.In recent years,Ligusticum chuanxiong Hort.a authentic Chinese medicinal material has been strongly polluted by heavy metals which seriously affected the quality and safety of medicine,and its effect on human health is of great concern.In this study,L.chuanxiong collected from the authentic production region of Sichuan province was used for the simulation of soil experiment.The physiological effects of Cd and Pb combined stress on the growth of L.chuanxiong were investigated.The physiological performances such as plant growth and development,photosynthetic physiology,subcellular distribution and chemical forms of Cd and Pb were analyzed under Cd and Pb combined stress.The aims of the present study are to reveal the physiological mechanism of L.chuanxiong in response to Cd and Pb contamination and to explore the environmental effects of heavy metal contamination on medicinal plants.This provides the scientific basis for controling the quality of soil environment and ensuring the safe production of Chinese medicinal materials.The main research results are as follows:（1）The different concentrations of Cd and Pb combined treatment on the inhibition effect of growth in L.chuanxiong was weaker than Cd or Pb single stress.The Cd and Pb combined treatment significantly the dry weight of roots,rhizomes,leaves and the proportion of rhizomes,significantly increased the content of Mg,Cu and N in underground parts,and significantly increased the content of Mg,P and Ca in aboveground parts.Weakened photosynthesis inhibition,net photosynthetic rate,intercellular CO₂concentration,stomatal conductance,transpiration rate,chlorophyll content,Fv/Fm,ΦPSII increased significantly,NPQ significantly reduced under Cd and Pb combined treatment.At the same time,the content of superoxide anion,free proline and malondialdehyde in leaves of L.chuanxiong was decreased.（2）Compared with the single Cd or Pb stress,the content of Cd and Pb in roots,rhizomes and leaves was significantly reduced under Cd and Pb combined treatment.Pb decreased the enrichment of Cd but increased the transfer of Cd,and Cd decreased the enrichment and transfer ability of Pb.Under the Cd and Pb combined treatment,the increase concentration of Pb promoted the absorption of Cd²⁺in roots apical meristem then increased the content of Cd in roots,rhizomes and leaves.However the increase concentration of Cd inhibited the absorption of Pb in L.chuanxiong and reduced the accumulation of Pb in plants.（3）At the subcellular level,Cd mainly exists in the cell soluble part of leaves,and Pb mainly exists in the cell wall.Under the Cd and Pb combined treatment,Pb significantly reduced the content of Cd in the soluble parts of cells and organelles,significantly increased the content of Cd in cell walls,and Cd significantly reduced the content of Pb in each component of cells.Cd and Pb in rhizomes mainly exist in cell walls.Pb significantly increased the content of Cd in cell walls,but significantly reduced the content of Cd in soluble parts of cells.Compared with single Cd or Pb treatment,Cd significantly reduced the content of Pb in cell walls,organelles and soluble parts of cells.There were more O-H,N-H,C=O functional groups in rhizomes and more O-H,N-H,C=O functional groups in leaves under 2 mg kg^-1Cd²⁺and 300 mg kg^-1Pb²⁺conditions.（4）Cd in leaves mainly exists in highly toxic chemical forms of ethanol and deionized water.Compared with Cd or Pb single treatment,Cd and Pb combined treatment significantly reduced the content of Cd in ethanol-extractable forms and water-extractable forms,and significantly increased the content of acetic acid-extractable forms,hydrochloric acid-extractable forms and residue-extractable forms.Pb in leaves was mainly extracted in the form of Na Cl and acetic acid,while Cd and Pb combined treatment significantly increased the content Pb of Na Cl,acetic acid,hydrochloric acid and residual extractable.In rhizomes,the chemical forms of Cd and Pb was dominated by the Na Cl,acetic acid and hydrochloric acid-extractable forms.The Cd and Pb combined treatment can promote the chemical content of Cd and Pb in the less toxic extraction states of Na Cl,hydrochloric acid,acetic acid and the residue.（5）As for secondary metabolites,compared with the single Cd treatment,the Cd and Pb combined treatment significantly increased the content of ferulic acid,tetramethylpyrazine and ligustilide.Compared with the single Pb treatment,the Cd and Pb combined treatment significantly increased the content of tetramethylpyrazine in rhizomes.The content of Cd in rhizome was negatively correlated with ligustilide,ferulic acid and tetramethylpyrazine.However the content of Pb was negatively correlated with tetramethylpyrazine.