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The thesis deals with studies on chemical structures and allelopathic effects of the Pistia stratiotes L., an exotic invasive plant cultivated in Dian chi of Kunming, Yunnan province.Sixteen compounds were isolated from Pistia stratiotes L. by the method of column chromatography with silica, Al2O3,Sephadex LH-20, Toyopearl HW-40F and RP-18 gel,and eleven compounds were identified by spectral analysis (MS,1H-NMR,13C-NMR, HMBC, H-HCOSY, HSQC). Their structures were elucidated as: (24R) - ergosta - 7, 22 - diene-3β, 5α, 6β-triol (1) 7β-hydroxysitosterol (2) sitoindoside I (3) soya-cerebroside I (4) luteolin (5) chrysoeriol 4′-O-β-D-glucopyranoiside (6) Stigmasta-5, 22-diene-3, 7-diol (7) inosine (8) annuionone E (9)β-?sitosterol (10) daucoterol (11). Compounds 1～9 were obtained from this plant for the first time.Allelopathic effects of the Pistia stratiotes L.toward the seeds of Lactuca sativa and Brassica campestris have been carried out. The results showed that the ethyl acetate phase have obvious inhibition on the seed germination and the growth of young roots and buds.The inhibiting rate of Lactuca sativa on the seed germination was -14.29%,52.38%,100%,100% at 0.00 01 g·ml-1,0.001 g·ml-1,0.01 g·ml-1,0.02 g·ml-1, and the growth of young roots and buds were 4.01%,60.65%,100%,100% and 14.41%,51.63%,100%,100%; while the Brassica campestris were -13.64%, 18.18%, 68.18%, 72.73%; -0.26 %, 13.95%, 29.40 %, 61.86% and -8.68%, 26.68%, 30.70%, 43.01%。
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