Study On Secondary Metabolites And Mechanism Of Allelopathy Of Ailanthus Altissima And Licorice

The natural phenomenon that plants and microorganisms can harmfully or beneficially affect the growth and development o f biological system by releasing secondary metabolites into the environment is defined as allelopathy.Allelopathic plants are one of the important resources for the discovery of bioherbicides.In this project,we studied the inhibitory effect of Ailanthus altissima(Mill.)Swingle extract on lettuce and the mechanism of the allelopathy of isoliquiritigenin on lettuce.A.altissima is widespread in C hina.In order to further explore the allelochemicals in A.altissima,lettuce was used as the recipient plant to guide the separation of crude extracts.Fourteen compounds were separated from the A.altissima by using chromatographic methods.On the basis of physico-chemical properties and spectroscopic analysis,their structures were identified as follows : 3?,20 S,24R,25-tetrahydroxydammarane(1),3?,20 S,24R,25-tetrahydroxydammarane(2),gardaubryone C(3),12?-hydroxyocotillone(4),hispidol B(5),piscidinol A(6),altissimanin B(7),23,24,25-trihydroxytirucall-7-en-3,6-dione(8),2,3-dihydroxypropyl(9),vanillic acid(10),p-hydroxybenzoic acid(11),shinjulactone C(12),shinjulactone B(13),cantin-2,6-dione(14).By using the method of biological monitoring in laboratory found that compounds 1,2,12 and 14 had a significant inhibitory effect on lettuce.When the concentration of cantin-2,6-dione was 100 ?M,the inhibitory effect on lettuce seedling radical length reached 49%.Isoliquiritigenin,a natural flavonoid of chalcone,has been recognized as an allelochemical with phytotoxicity to lettuce,however,not enough attention has been paid to the mechanisms of this secondary metabolite.In this work,we investigated the physiological and biochemical mechanisms of isoliquiritigenin on lettuce seedlings.The results show that isoliquiritigenin has a concentration-dependent inhibitory effect on radicle length of lettuce seedlings,but no significant effect on lettuce germination.Microscopy analyses suggest that the surface morphology of lettuce radicle was atrophied and the intracellular tissue structure deformed at high concentrations.Isoliquiritigenin induced the overproduction of reactive oxygen species(ROS),which led to loss of cell viability in the radicle cells.In addition,malondialdehyde that a product of lipid peroxidation and free proline levels were found to have increased,while chlorophyll content in lettuce seedlings decreased.All these changes suggest that the primary allelopathic mechanism of isoliquiritigenin by which it inhibits radicle length in lettuce seedlings might be due to the overproduction of ROS,which causes oxidative damage to membrane lipids and cell death.This study is the first to study the secondary metabolites of A.altissima by using guided separation method,and found 4 compounds with allelopathic potential(1,2,12,14),which proves for the first time that carbolin alkaloids have allelopathy.The mechanism of the allelopathy of isoliquiritigenin for the first time is based on the induction of reactive oxygen species in lettuce cells,which leads to a decrease in cell viability and ultimately affects the growth and development of seedlings.The results provide experimental basis for the development of biological herbicides using allelopathic plants A.altissima and Glycyrrhiza uralensis Fisch.