Study Of Melittin On The Inhibiting Effect To The Pathogenic Microbe And Physiological Effect Of Crops

The antimicrobial spectrum and antimicrobial mechanism of melittin on nearly 20 species pathogen were studied, and the effects of melittin on the physiological indices of crops and the defensive enzymes of maize at growth stage were mensurated systematically. The results showed: melittin can inhibite the activity of Grampositive, Gram-negtive bacteria, several species pathogen bacteria and pathogen fungi of crops , which indicated that melittin had wide inhibition spectrum. The inhibiting curve showed the capacity of melittin killing pathogens quickly; SDS-PAGE made it clear that there was no secific change to the protein expressing in Erwinia carotowora subsp.carotovora with the effect of melittin, and the result proved melittin inhibiting the activity of pathogens was not through acting on the proteins expressing and effecting metabolizition. Observation under scanning electronmicroscope revealed that the surface of structure of Erwinia carotowora subsp.carotovora was destructed with several holes by melittin. Those holes result in leakage of contents of bacterium. Observation under transmission electron microscope also revealed that. The results above indicated; the inhibiting mechanism of melittin on pathogen of crops was that the cell membranes and the cell walls of the bacterium were made holes which resulted in the breach of cell membranes,then the leakage of contents in the cells, at last dead. Observation under scanning and transmission electron microscope were also made to Fulvia fulva ---a sort of fungus, that revealed cytoplasm concentrated,cell membrane separated from cell wall,while cell membrane was not broken down into a cavity, the phenomenon showed the inhibiting mechanism of melittin on prokaryota and eukaryota was different.It was found that the effects of melittin on the four cultivars of crops was similar----the content levels of chlorophyll, soluble sugar, nucleic acid and protein were promoted by the low concentration(5 mg/L), and inhibited by the higher (50 mg/L), although the effects were not significant(t-test, p>0.05). Melittin can induce the activity of the defensive enzyme of crops: PAL and PPO reached the maximal levels 48 hours after spraying the solution of melittin (5 mg/L), which were led to increase of 178% and 9.8% respectively compared to the control; SOD was increased by 31.5% after 6 hours. The activity of POD reach the maximal levels at the concentration 50mg/L.The study of POD isoenzyme of maize elucidated further that melittin influenced the defensive enzymes: induction to some zymogram band (P11)while inhibition to other zymogram,, and the effect were not uniform to the different cultivars of maize, which showed the particularity of cultivars.