| Verticillium dahliae is a destructive soil borne fungus that penetrates the host cottonthrough the roots and spreads systematically through the xylem. Nowdays, the economic loss inthe world caused by Verticillium wilting averages about one thousand million every year. Morerecently, many a major Chinese cotton area is severely damaged by the disease, being recognizedas a serious threat to cotton production with high and stable yield in our country, especially whensuffering from defoliation type of Verticillium wilting. Why no significant advance has beenachieved in the disease prevention and the disease-resistant breeding of Verticillium wilting oncotton, besides being devoid of immunological antigens, it is mostly due to that the basicresearch on the mechanism of Verticillium pathogenesis lie in a behind situation relatively.More and more studies proved that the toxin secreted by Verticillium dahliae (orVerticillim albo-atrum )was a key factor to cause the Verticillium wilting. So to explore theproperty of wilting toxin and understand its structure and function is undoubtfully a basicresearch content necessary to reveal the pathogensis mechanism of Verticillium dahliae.In the paper, we adopted the technology of Fast Protein Liquid Chromatograph abbreviatedto FPLC, some physiological and biochemical characteristics of wilting toxin secreted by T9VD8 and SS-4, three typical isolates of Verticillum dahliae on cotton, were studied. The mainresults are as follows:　1. There was some relationship between the output of filtrating toxin and the PH of media.The output of toxin coming from the media of pH4.8 was higher than that of pH6.8. Duringdefinite time, the crude toxin appeared to increase with the prolongation of culturing time. Theyield of toxin from being cultured for 21 days was 4.07ug/ml more than that of 15 day's. Inaddition, compared with cultured in the dark, the yield of toxin was lower under cultured in thelight, their average output of toxin secreted by three isolates of Verticillium dahliae wasreduced about 3.3ug/ml.　2. PH changes of the filtrate took place during culturing the isolates of Verticillium dahliae.The PH of the filtrate appeared to increase after isolates, T9 ,VD8 and SS-4, to be cultured. Theincrement scale of pH4.8's medium was larger than that of pH6.8's, and the one with cultured for21 day's was higher than that of 15 day's. The pH increase during culturing Verticilliumdahliae implicated that it might be necessary for H+ provision to multiply the pathogensis.3. The peak value of salting out toxin secreted by V. dahliae was in the 70-80%saturation of ammonium sulfate. So 90% saturation of ammonium sulfate was enough for toxinin the filtrate to be precipitated and then to use in further separation and purification.4. Wilting toxins can induce to block the xylem of cotton seedling. Observation throughelectron microscope showed that the vessels of cotyledon veins were plugged by black tyloses,and parenchyma cells coming from cotyledon veins deformed and abnormally arranged, thediameter of stem vessels became so narrow as to hinder water conducting fluently along it.5. Crude extracting toxins of three Verticillium dahliae strains were separated into twoactive peaks by the gel filtrating column of Superose 12. The first peak's has weak wilting abilityto show the symptom of yellowish wilting type on the cotton seedling with normal root system.The second peak's results in strong wilting to induce severe greenish wilting. Furthermore, thesecond peak's toxin loses after dialysed by the dialyser of MWCO 8000-10000 Daltons, So wecannot use the dialyser or superfiltrator of 10000 or more dalton's molecular weight in the study... |
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