Extraction of Flavonoids and Polyphenols from Coronatinetreated Mulberry Leaves and Evaluation of Their Antibacterial Activity against Pseudomonas syringae

摘要

Flavonoids and polyphenols are the main secondary metabolites in mulberry leaves,which have multiple biological functions such as antibacterial activity,free radical scavenging activity and antioxidant activity.In this paper,the parameters for the extraction of flavonoids and polyphenols from coronatine(COR)-treated mulberry leaves were optimized,and the components of the extracts were analyzed by high performance liquid chromatography(HPLC),and their antibacterial activity against Pseudomonas syringae,which causes mulberry bacterial blight,was evaluated in vitro to explore the mechanism how COR acted as a plant immune elicitor to improve the resistance of mulberry to bacterial blight.The results showed that ethanol concentration of 70%,extraction temperature of 80℃,extraction duration of 6 h and solid-liquid ratio of 1∶40 were the optimal parameters for the extraction of flavonoids and polyphenols from mulberry leaves.Flavonoids and polyphenols were mostly distributed in ethyl acetate and n-butyl alcohol fractions which showed better antibacterial activity than petroleum ether,dichloromethane and water fractions.Meanwhile,the antibacterial activity of ethyl acetate and n-butyl alcohol fractions of COR-treated mulberry leaves were more evident than that of water-treated mulberry leaves.Scanning electron microscopy showed that flavonoids and polyphenols inhibited the growth of pathogenic bacteria by changing cell morphology,damaging cell wall structure and unbalancing cell osmotic pressure.HPLC analysis confirmed the contents of morin,quercetin,quercitrin,kaempferol,chlorogenic acid and rutin were increased to a different extent in COR-treated mulberry leaves.So it can be concluded that the increased contents of flavonoids and polyphenols induced by COR may be one of the reasons for the enhanced resistance to mulberry bacterial blight.