| Marine bacterium AiL3strain which was isolated from mangroves had beenshown to be antagonist against many plant pathogenic fungi including Colletotrichumgloeosporioides. And the antimicrobial substance secreting from the strain wasproved to be proteins. In this paper the purification of the antifungal proteins and theproteins bio-control efficacy and mechanism on mango anthracnose were studied. Themain results were obtained as follows:1. The antifungal proteins of AiL3strain fermentation broth were extracted by40%~50%ammonium sulfate precipitation, then treated at121℃for20min, andchromatographied by Sephadex G-50. The purified protein was demonstrated to aband of28kD by SDS-PAGE. This protein included18amino acids． Thisantagonistic protein was treated at121℃for20minutes without losses of antifungalactivities which meant that it was resistant to high temperature. This antagonisticprotein was also active to C. gloeosporioides from pH5.0to10.0. UV radiation hadno significant effect on the antifungal activity of the protein.2. The antifungal protein of AiL3strain was used to control anthracnose ofpostharvest mango. The result showed that it had control efficacies of27.3,38.2and45.1%respectively when the fruits of mango were treated with20,40and60μg/mLprotein. The control efficiency of60μg/mL antifungal protein of AiL3strain wassignificantly higher than43.6%of the chemicals Sportak. The bio-control mechanismof the antifungal protein to anthracnose of postharvest mango was studied and theresults showed that: the contents of soluble protein and MDA and the activities ofdefense enzymes of disease in antifungal protein treatment were compared with thesein PB and sterile water treatments. The content of soluble protein increased while thecontent of MDA decreased; the activity of superoxide dismutase （SOD）,phenylalanine ammonia lyase （PAL） increased, but peroxidase （POD） activitydecreased. Thus antifungal protein of AiL3strain could increase the content of solubleprotein, and decrease the content of harmful substance such as MDA in mango,meanwhile it could also increase the activities of some defense enzymes. All of these may inhibit the development of anthracnose of postharvest mango.3. The inhibition mechanism of antifungal protein of strain AiL3against C.gloeosporioides was studied. The influences of antifungal protein on mycelium andspore were observed by scanning electron microscope. The antifungal protein not onlyinhibited the hyphal growth, but also caused a series of marked hyphae morphologicaland cell structural alterations including excessive branching, constriction, sunken andbreaking of hyphae, the contents of hyphae exuded and the hyphae became branchedsmall fragments. The spores of C. gloeosporioides were swelled and broken, thecontents of spores exuded and left the spore a vacant shells. AiL3antifungal proteininfluenced the cell membrane and cell wall, and also influenced the DNA, protein andsugar metabolisms of C. gloeosporioides. The antifungal protein could alterpermeability of cell membrane and cause the contents of hyphae exuded, but it had noeffect on the chitin content of cell wall. The antifungal protein could increase sugarand protein contents of the mycelium, but it had no effect on DNA content. |
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