| New Ag-antibiotic 702 produced by Streptomyces 702 have significant antifugal activity, but its antifugal mechanism is not yet clearly. In order to further explore new pesticides, we preliminary studied the inhibition of R. solani and its antifugal mechanism. The results are as follows:(1) Study on the effect of new Ag-antibiotic 702 against mycelium morphology, mycelial biomass, the number of sclerotia and quality as well as sclerotia germination of Rhizoctonia solani by microscope observation and mycelial dry weight. The results showed that after 4.67 μg/mL of new Ag-antibiotic702 treated, the length of fungus newborn branch, diameter significantly the branch spacing of Rhizoctonia solani than the control 65.39%,26%,75.98% shorter. Treated by new Ag-antibiotic702, mycelium shriveled, wrinkled, bacterial cells particulate matter under the microscope. In culture medium containing 6.0 μg/mL of new Ag-antibiotic702, the growth of Rhizoctonia solani mycelium was strong inhibition and mycelium biomass was 48.15% less than control. When the concentration of new Ag-antibiotic702 was up to 100μg/mL, the sclerotia formation rate was only 1.22% than controls, the sclerotia dry weight was 99.93% compared with the control. And when the concentration of new Ag-antibiotic702 was up to 350μg/mL, the rate of sclerotia germination inhibition was up to 73.33%. Preliminary exploration result showed that the new Ag-antibiotic702 has a significant impact on Rhizoctonia solani at different stages of growth and development.(2) Using different concentrations of new Ag-antibiotic702 treat target fungus, and then determined the content of total sugar, protein and fat in target fungus. The results showed that by 1.0,1.5,3.0,4.5,6.0 μg/mL of new Ag-antibiotic702 treated, the total sugar in Rhizoctonia solani were 92.88,111.27,106.47,96.00,91.74 mg/g, with the control 82.04 mg/g, at first showing a downward trend and then upward, and all were higher than the control. The content of fat was first decreased and then increased and decreased. The contents of protein were 54.15,66.82,67.60,54.84,45.81 mg/g, and the control was 50.16 mg/g, showing a downward trend at first and then upward, showing a significant difference. That indicate the Rhizoctonia solani metabolism disorders treated by new Ag-antibiotic702.(3)The effect of new Ag-antibiotic702 on Rhizoctonia solani protein bands was determined by SDS-PAGE method. SDS-PAGE results showed that after the treatment by 4.67μg/mL new Ag- antibiotic 702, original 15 fungus protein bands reduced to 8, and the bandsstrength was significantly weakened. Indicated that the new Ag- antibiotic 702 may be caused fungus protein leakage or degradation(4) The effect of new Ag-antibiotic 702 on the biological barrier was studied. The infrared spectra showed that the only role of New Ag-antibiotic 702 against cell wall is reducing the degree of crosslinking of the dextran, so that the cell wall structure is unstable, and easily broken. A significant influence on the cell membrane, such as after 1.55μg/mL of new Ag-antibiotic702 treated 48 hours, the sugar utilization rate was decreased by 29.9%. After 6.0μg/mL of new Ag-antibiotic702 treated 210 minutes, the content of Ca2+, K+ was only 41.2%,50.5% of the control, and Na+K+-ATPase activity decreased by 83.11%, and Ca2+Mg2+-ATPase activity decreased by 55.57%. When treated 300 minutes by 6.0 μg/ML of new Ag-antibiotic702, the accumulation of hydrogen peroxide was increased by 118.61% compared with the control.The site action of new Ag-antibiotic702 may in the cell membrane for further exploration.(5) Finally, determined the synthesis of ergosterol in Rhizoctonia solani by thin layer chromatography. Provided the site action of new Ag-antibiotic702 was the cell membrane ergosterol by UV scanning and addition of ergosterol method. Thin layer chromatography proved that new Ag-antibiotic 702 cannot restraint the synthesis of ergosterol. The UV scanning and addition of ergosterol showed when the new Ag-antibiotic702 and sterols were mixed and incubated for 4 h, ultraviolet absorption spectrum of the mixture produced a obviously hypochromic effect. Mixed the new Ag-antibiotic 702 and sterols into the culture medium cultured 48 hiours, the colony diameter is only 3.68, compared with the control decreased by 60.04%. That indicated sterols can combine with new Ag-antibiotic 702, caused its structure changed, so that the target of the new Ag-antibiotic 702 is ergosterol in the cell membrane.In a word, the antifugal mechanism model of new Ag-antibiotic 702 is as follows: destroy the structure of cell wall firstly, so that pesticides are able to through the cell wall and into cell membrane, and combine with ergosterol to form of ergosterol- antibiotics composite. In the end, the structure and physiological function of the cell membrane are changed; leading to the fungus’s metabolism and energy metabolism disord, eventually leading to fungus dead. |
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