The Study Of The Structures And Allelopathy Of Glycoalkalods From Solanum Nigrum L

Glycoalkaloids are important secondary metabolites produced by numerous Solanum plants, they possess significant defense function such as toxicity to animals, inhibition to the growth of microbiology, and allelopathic effect on plants. Solamargine and solasonine are the main glycoalkaloids present in Solanum nigrum L. They share the same aglycone solasodine, but differ in their trisaccharide chain. The sugar chain attached to solamargine is chacotriose, while to solasonine is solatriose.In this paper solamargine and solasonine were separated and purified from Solanum nigrum L. The compounds were identified by TLC,HPLC and 13C NMR. The purity of the two compounds was more than 95% checking by HPLC.Bioassay results showed that solamargine and solasonine had no effect on germination of cucumber (Cucumis Sativa L) and lettuce (Lactuca Sativa L) seeds, However, they inhibited the radicle growth of cucumber and lettuce. The inhibition effect was concentration-dependent and the IC50 value of solamargine to cucumber and lettuce radicle growth was 0.53 and 0.33 mM, respectively. The IC50 value of solasonine to cucumber and lettuce radicle growth was 0.58 and 0.38 mM, respectively.In a 1:1 combination solamargine and solasonine expressed synergistic effect in inhibiting cucumber and lettuce radicle growth, the inhibition of the mixture was larger than the sum the their indiduvual inhibition effect in same concentration. Isoblediagram was used to assess possible antagonism, synergism or response addition of solamargine/solasonine in different ratios (3:1, 2:1, 3:2, 1:1, 2:3, 1:2, 1:3) in inhibiting cucumber radicle growth. The results showed solamargine and solasonine expressed synergistic effect in the ratios of 3:1, 2:1, 3:2, 1:1. The maximal synergism was in the ratio of 2:1. In contrast, solamargine and solasonine was antagonistic in the ratios of 2:3, 1:2, 1:3.In order to study the structural influence to the allelopathic activity of the glycoalkaloid, 6-O-sulfated solamargine was prepared. The allelopathic effect was tested and the results showed that 6-O-sulfated solamargine had no inhibition effect yet on the germination of cucumber as well as lettuce seeds, and the inhibition effect to the radicle growth of the two species disappeared also, in lower concentration it even accelerated the radicle growth of the two plants. The result indicated that 6-hydroxy group of solamargine played an important role on allelopathic effect.