A Research On The Effect Of Exogenous Ascorbic Acid And Melatonin To Mitigate The SO₂ Toxicity Of Hosta Plantaginea

In recent years,many cities in China are subject to different degrees of air pollution due to the industrialization and urbanization process accelerated.Sulfur dioxide is harmful for the plant,and it occurred mostly in the strong leaves physiologically.In the atmosphere.urban ground cover plants absorb contaminants inevitably,he ground cover plants now become one of the main greening materials of urban landscape,so sulfur dioxide is the main object of remediation of air pollution in China at this stage.Therefore,it is of great significance to clarify the effect of sulfur dioxide pollution on growth and development of urban ground cover plants and to explore ways to alleviate SO₂ toxicity.SO₂ easily reacts with water to produce sulfurous acid in which enters the plant and causes damage to the plant in the form of its derivative Na2SO3-NaHSO3（3:1）,So we use the mixed spraying method to simulate the SO₂ pollution in the atmosphere.In our study,greenhouse pot experiment was conducted to explore the regulations metabolism of the contamination of different exogenous AsA,MT,AsA and MT mixture（400μmol/L、200μmol/L、400μmol/L+200p,mol/L）on the Hosta plantaginea in a certain concentration of SO₂（200mmol/L）,to measured the response of leaves,several physiological and biochemical indexes to the SO₂ stress,to verified the optimal application concentration of the exogenous substances to mitigate the SO₂ toxicity of the urban landscape ground cover plants.The effect of SO₂ on the growth of urban ground cover plants and the way to alleviate SO₂ stress were discussed.The future can be applied to municipal environmental protection operations,in practice to alleviate the urban greening ground cover plants by the atmosphere of SO₂ damage.The results are as follows:（1）Hosta leaves showed a large area of yellowish-brown spots and few curly,the wounded leaves were even transparent when treated with the concentration of the SO₂（200mmol/L）.The leaf chlorophyll,the relative content of water,the leaf pH value of the Hosta,the contents of AsA and GSH showed a declining trend compared with the control,Because SO₂ enters the cell through the cell membrane to destroy the functional structure within the cell.however,cell membrane permeability,malondialdehyde content,Soluble content,proline content,the activities of SOD,POD,CAT,APX and GR,production rates and accumulative amount of the H2O₂ is increasing compared with the control.Indicating that Hosta plantaginea in the external environment by the stress will stimulate their own stress protection system,So that the antioxidant enzyme activity increased to consume the body of reactive oxygen species,but there is limited in its ability to resist SO₂,So the accumulation of hydrogen peroxide and superoxide anion production rate are rapidly increasing the destruction of cell ion balance in the body,damage the cell membrane system.（2）Spraying a certain concentration of exogenous ascorbic acid AsA and exogenous melatonin MT can significantly alleviate the SO₂ stress,improving the Hosta plantaginea’s status,and the addition of AsA and MT mixed treatment is the best results,which can be directly from the Hosta plantaginea’s leaf injury symptoms.（3）Spraying appropriate concentration of exogenous AsA,MT,AsA and MT mixture can effectively alleviate the SO₂（200mmol/L）stress,thereby improving their victimization symptoms and growth conditions.The leaf chlorophyll,the relative content of water,the leaf pH value of the Hosta,Soluble content,the activities of SOD,POD,CAT,APX and GR,the contents of AsA and GSH were higher than those under the SO₂ stress,and the addition of AsA and MT can effectively supplement AsA and GSH content.The cell membrane permeability,malondialdehyde content,free proline content,accumulation of hydrogen peroxide and superoxide anion production rate were significantly lower than that under the SO₂ stress.Indicating that AsA and MT slow the accumulation of reactive oxygen species.（4）By analyzing the indexes,it is speculated that the main mechanism of AsA and MT to alleviate SO₂ stress may improve the activity of antioxidant enzymes,supplemented with endogenous antioxidants to inhibit the production of reactive oxygen species,and protect the stability of the cell membrane,So that Hosta plantaginea in the SO₂ environment has not been rapidly acidified to ensure the normal growth and metabolism of the conduct.（5）The combination of various factors shows that plants in adversity environment through the absorption and utilization of foreign substances to resist the adverse environment.The results showed that exogenous AsA and MT could alleviate the toxicity of Hosta plantaginea to SO₂ stress,but spraying exogenous AsA and MT mixed solution（400μmol/L + 200μmol/L）showed the best alleviation to the toxicity of Hosta plantaginea to SO₂ stress.