Studies On The Biological Activity Of Plants And The Active Substances Of Clausena Lansium

Searching for bioactive substances from plant resources is of great significance to the research and development of botanical pesticides and new medicines.In this article,23common medicinal plants were taken as that research object,the plant components were extracted by organic solvent extraction.With 8 species of plant pathogenic fungi and 9species of animal pathogenic bacteria as tested bacteria,the antimicrobial activity of 23 plant methanol extracts was screened by mycelium growth rate method and toxic plate coating method.The active substances of Clausena lansium leaves extract were isolated by two-phase solvent extraction,and the antimicrobial activity and antioxidant activity of each extract were determined.Furthermore,using silica gel column chromatography,silica gel thin layer chromatography and other chromatographic separation techniques,combined with activity tracking,the antimicrobial substances of Clausena lansium leaves with good antimicrobial activity was isolated and purified,and the structures of the active substances were identified by gas chromatography-mass spectrometry（GC-MS）,and the antimicrobial action mechanism of antimicrobial compounds were preliminarily explored.The results are as follows:The results of antimicrobial activity screening showed that the methanol extracts of Clausena lansium,Myrica rubra,Ipomoea cairica,Conyza sumatrensis,Praxelis clematidea and Phytolacca acinosa had good antifungal activity against tested plant pathogenic fungi,among them,the antifungal activity of methanol extract from Clausena lansium leaves is obvious and broad-spectrum.The methanol extracts of 15 kinds of plants,such as Clausena lansium,Myrica rubra,Wedelia chinensis,Praxelis clematidea,Conyza sumatrensis and Ipomoea cairica,have antibacterial activity against at least one kind of tested animal pathogenic bacteria,among which the methanol extract of Clausena lansium leaves and Myrica rubra leaves has obvious and broad-spectrum antibacterial activity.On the basis of antimicrobial activity screening,the EC₅₀ values of methanol extracts of 6 kinds of plants against tested plant pathogenic fungi and the MIC values of 15 kinds of plant methanol extracts against tested animal pathogenic bacteria were further determined by growth rate method and toxic plate coating method.The results showed that the EC₅₀ of methanol extracts from Clausena lansium leaves to 8 kinds of tested plant pathogenic fungi was 0.0332 mg/m L～5.1727 mg/m L,of which the virulence to Exserohilum turcicum was the highest.The EC₅₀ of the other 5 plant extracts to tested plant pathogenic fungi was 0.0803mg/m L～6.1889 mg/m L.The MIC values of methanol extracts from Clausena lansium leaves to 9 species of tested animal pathogenic bacteria were 0.625 mg/m L～2.5 mg/m L,and the MIC values of methanol extracts from other 14 plants to the tested pathogenic bacteria were0.625 mg/m L～10 mg/m L.The methanol extract of Clausena lansium leaves was separated by two-phase solvent extraction,and the petroleum ether extract,ethyl acetate extract,n-butanol extract and extractive residue were obtained,and the antimicrobial activity of different extracts was determined.The results showed that the petroleum ether extract had strong antifungal activity,its EC₅₀ value against 8 kinds of tested plant pathogenic fungi was 0.0102mg/m L～0.7441 mg/m L,and its mycelium virulence to Exserohilum turcicum was the highest,and the MIC value of petroleum ether extract to 9 kinds of tested animal pathogenic bacteria was 0.1563 mg/m L～1.25 mg/m L,among which the antimicrobial activity was strong against Micrococcus luteus,Bacillus cereus and Micrococcus lysodeikticus,and thier MIC values were all 0.1563 mg/m L.In addition to antimicrobial activity,the methanol extract from Clausena lansium leaves and its 4 extracts showed different degrees of antioxidant activity,among which ethyl acetate extract and n-butanol extract had strong scavenging ability to DPPH free radical,and ethyl acetate extract had strong scavenging ability to hydroxyl radical.Taking Ceratocystis paradoxa as indicator fungus,under the guidance of activity tracking,the antimicrobial active substances of petroleum ether extract from methanol extract of Clausena lansium leaves were separated by silica gel column chromatography and silica gel thin layer chromatography,and other chromatographic techniques.The active substances were identified by gas chromatography-mass spectrometry（GC-MS）,3 active compounds were identified as benzaldehyde,p-cresol and 4’-methylacetophenone.The results of antimicrobial activity determination showed that the 3 active compounds had certain inhibitory activity against all tested pathogen,among which p-cresol and 4’-methylacetophenone had better inhibitory effect on Exserohilum turcicum and Pestalotiopsis theae,and benzaldehyde had better inhibitory effect on Proteusbacillus vulgaris,Staphylococcus aureus,Bacillus anthraci,Bacillus megaterium,Bacterium paratyphosum B,and Bacillus cereus.Using Ceratocystis paradoxa,Exserohilum turcicum,Bacillus cereus and Staphylococcus aureus as tested pathogen,the antimicrobial mechanism of benzaldehyde,p-cresol and 4’-methylacetophenone 3 compounds was preliminarily explored.It was found that when treated with 3 compounds,the cell membrane permeability of the tested pathogens changed,the relative permeability increased and the content of soluble protein decreased,indicating that antimicrobial compounds can interfere with the synthesis and metabolism of mycelia,destroy the cell structure of the bacteria and cause the leakage of the substances in the cell,thus affecting the growth and reproduction of the pathogens.