Bioactivities And Modes Of Action Of Four Kinds Of Natural Products

Worldwide,pathogens and pests pose a serious threat to the development of agriculture,and cause the large economic losses.Now,chemical agents are still the main strategy for controlling agricultural pests.However,the long-term use of chemical pesticides has resulted in some side effects for the agro-ecosystems and humans,especially for“3R”problem,pesticide residues,resistance and pest resurgence.Due to the significantly bioactivities,biodegradation,and a lack of harmful effects on non-target organisms and other advantages,natural products have been attracted many people`s interests and become an alternative choice for pest management.In this work,we firstly studied the antifungal,insecticidal and acaricidal activities of three indoloquinoline alkaloids,eight simple phenylpropanoids,twenty-one quinones and eighteen coumarins against phytopathogenic fungi,including Rhizoctonia solani,Magnaporthe oryzae,Fusarium graminearum,Botrytis cinerea,Sclerotinia sclerotiorum,ect.,and two pests?Nilarparvata lugens,Mythimna separata?and one ectozoic parasite Psoroptes cuniculi.Then,the modes of action of some active compounds were investigated.This study laid the foundation for the future development of these kinds of compounds as alternative and environmentally friendly bioagents.1.The antifungal activities of indoloquinoline alkaloids and its mechanism of action.In this study,we firstly screened the antifungal activities of three indoloquinoline alkaloids cryptolepine,isocryptolepine and neocryptolepine against R.solani and M.oryzae.Results showed that neocryptolepine has the best antifungal activity,and a wide antifungal spectrum also proved in the following test.Then,integrated proteomics,RNA-Seq,surface plasmon resonance?SPR?and other biotechnologies,we found that neocryptolepine inhibited complex III activity of mitochondrial respiratory chain in the oxidative phosphorylation pathway by binding to Fe-S protein?Cytochrome b-c1 complex subunit Rieske?,and then resulted in the dead of R.solani.Meanwhile,it also could affect the structure and function of cell nucleus and inhibit DNA synthesis.2.Antifungal,insecticidal and acaricidal of simple phenylpropanoids and the mechanism of acaricidal activity.In the current work,we firstly screened the antifungal activities of eight simple phenylpropanoids against R.solani,M.oryzae,F.graminearum,B.cinerea and S.sclerotiorum,and results showed that except to F.graminearum,compounds presented the various toxicity against four fungi,and isoeugenol has the better activity against S.sclerotiorum with the inhibition rate of 86.05%at 50?g/mL.Eugenol showed the significant insecticidal activities against N.lugens,the LC₅₀value was 89.22?g/mL,and eugenol acetate presented the moderate toxicity against M.separata as well as the positive control toosendanin.Using RNA-Seq analysis and surface plasmon resonance analysis,we unveiled that eugenol inhibited complex I activity of mitochondrial respiratory chain in the oxidative phosphorylation pathway by binding to NADH dehydrogenase chain 2active-site amino acids Phe198,Glu211 and Lys288,and then resulted in the death of mites.Further experiments indicated that the difference in the complex I sequence between insects and mammals led to the different affinity of eugenol to specific peptides,resulting in species-specificity.Eugenol presented the significant inhibitory effects against mitochondrial membrane potential and complex I in Aedes albopictus C6/36 cells,but it was not active in rat PC12 cells.Insect cells were particularly sensitive to eugenol.In addition,it had better safety and did not result in Parkinson's disease or other diseases compared to the known inhibitor rotenone in rats.3.Antifungal,insecticidal and acaricidal of quinones and their mechanism of action.Among all tested quinones,plumbagin exhibited stronger and broader antifungal activity against eight phytopathogenic fungi(EC₅₀0 2.84-10.53?g/mL)compared to a commercial fungicide,azoxystrobin(EC₅₀0 20.40->100.00?g/mL).It significantly damaged the cell and mitochondrial membrane systems,changed the morphology,triggered the release of cellular contents and generate reactive oxygen species in R.solani mycelia.Emodin exhibited the highest insecticidal activity(LC₅₀0 84.30?g/mL)against N.lugens;and very moderate activity against M.separata(LC₅₀0 548.74?g/mL).It exhibited significant AChE and GST inhibitory activities.So,we thought that it may increase the sensitivity of insects to drugs by inducing P450 activity in the phase I reaction and then inhibiting phase II detoxification by inhibiting GST activity,the nerve conduction and motivate function also were blocked,and thereby promoting insect death.Juglone and plumbagin were observed to possess the strongest acaricidal activities against P.cuniculi,and these two chemicals completely cured naturally infested rabbits in vivo within 15 days.No skin irritation was found in all treated rabbits.Moreover,Juglone and plumbagin significantly inhibited AChE and GST activity with IC₅₀0 values of 29.87?g/mL and 32.69?g/mL,respectively,for plumbagin and 14.81?g/mL and 52.49?g/mL,respectively,for juglone.The cytotoxicity of plumbagin and emodin are strong against HL-7702 cells,and the former compound also presented the toxicity against Hacat cells,so,the clinic use of this compound should be studied further.4.Antifungal,insecticidal and acaricidal of coumarins and their mechanism of action.Among eighteen coumarins,4-methoxycoumarin?100?g/mL?presented the better antifungal activity against R.solani,and it distorted the cell membrane system and nuclear morphology,and induced the release of the cellular contents and the accumulation of reactive oxygen species,the mitochondrial membrane potential mycelia also were destructed.Sphondin presented the strongest insecticidal activity against N.lugens,exhibiting LC₅₀0 values of 122.66?g/mL.A moderate toxicity of 4-methoxycoumarin?500?g/mL?against M.separata was shown.Sphondin increase the sensitivity of insects to drugs by inducing P450 activity in the phase I reaction and then inhibiting phase II detoxification by inhibiting GST activity,Meanwhile,the nerve conduction and motivate function were blocked,thereby result in insect death.4-Methoxycoumarin has the better toxicity against P.cuniculi with the LC₅₀value of 34.18?g/mL.Sphondin and 4-methoxycoumarin presented the weak toxicities against two human cells.