| Parthenolide is a sesquiterpene lactone compound derived from Compositae or Magnoliaceae plants.It is a botanical secondary metabolite and was usually isolated from the leaves of Magnoliaceae plants.It has a strong inhibitory effect against plant pathogens,and as a plant-derived active ingredient,parthenolide has the characteristics of rich source,specific mode of action,low drug resistance risk,environmental friendly,and relatively safe to non-target organisms.Thus,it is an ideal candidate for developing novel control agent against plant pathogens and has good application prospects.In this study,8 kg of fresh leaves of Magnolia grandiflora Linn,were collected in Nanjing Botanical Garden Mem.Sun Yat-Sen after trimming.Parthenlide was extracted and isolated after pulverization by using multi-column chromatography and repeated recrystallization method,and its purity and structure were analyzed and determined with HPLC and NMR,respectively.As a result,6.5 g of parthenolide was obtained with a purity of 99.51%.The anti-microbial spectrum of parthenolide against 11 fungi,3 oomycetes,and 3 bacteria was determined by using mycelial growth rate method and turbidity method.The results showed that parthenolide is most effective against Xanthomonas oryzae pv.oryzae,and the inhibitory effect in vitro is better than that of control bacetericide bismerthiazol,with the EC50 value of 2.94 μg/mL and EC90 value of 7.69μg/mL.In addition,parthenolide also has good inhibitory activities against Sclerotinia sclerotiorum,Helminthosporium maydis,and Xanthomonas oryzae pv.oryzicola,and the EC50 values are 10.12μg/mL,10.03 μg/mL,and 4.38 μg/mL,respectively.The preliminary greenhouse pot experiment showed that parthenolide had protective and curative activities against rice bacterial blight,and its curative activity at 200μg/mL has no significant difference with that of bismerthiazol;rainwashing tolerance of parthenolide was analyzed,and the result showed that rainwashing severely afftects its antibacterial acitivity;effect of pH values on antibacterial activity of parthenolide was studied,which suggested that parthenolide is more effective against Xanthomonas oryzae pv.oryzae under neutral to slight acid condition;antibacterial activity of parthenolide against catalase deletion mutants of Xanthomonas oryzae pv.oryzae were determined,which showed that its antibacterial activity is directly associated with the catalase activity of mutants;effects of exogenous GSH,cysteine,NADH,NADPH,and catalase on the antibacterial activity of parthenolide were measured,and the results showed that exogenous compounds with free sulfhydryl groups such as GSH and cysteine and catalase can abolish its antibacterial activity,but important intracellular reductive compounds such as exogenous NADH and NADPH had no such effect,meanwhile LC-MS analysis showed that GSH and cysteine could react rapidly with parthenolide in vitro;the activities of parthenolide derivatives against Xanthomonas oryzae pv.oryzae were determined,which showed that exocyclic double bond of parthenolide is the key antibacterial group,and addition of exocyclic amino group can increase its antibacterial activity.In summary,parthenolide should be used under neutral to slight acid conditions,and rainwashing and combined application with biological nucleophiles such as compounds with free sulfhydryl groups should be avoided.In addition,five Xanthomonas oryzae pv.oryzae strains(R-1,R-2,R-3,R-4 and R-5)resistant to parthenolide were screened in vitro by using gradient drug taming method in this study,and the colony size and morphology of five resistant strains were not significantly different from those of wild type strain;the sensitivity of five resistant strains to parthenolide was determined,and the results showed that the five resistant strains were low-resistance strains;the pathogenicity of resistant strains on rice were assayed,which showed that the pathogenicity of resistant strains are weaker than that of wild type strain;sensitivity of resistant strains to commonly used bactericide bismerthizol was determined,and the results showed that parthenlide has no cross-resistance with bismerthizol.These results indicated that the resistance risk of Xanthomonas oryzae pv.oryzae to parthenolide is relatively low,and parthenolide has the potential to be used as control agent against rice bacterial blight.In conculsion,parthenolide has good biological activities against Xanthomonas oryzae pv.oryzae and low resistance risk,and can be futher studied as a lead for developing control agents against rice bacterial blight. |
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