Chromatographic Study of Activity of Euphorbia Eaegyptiaca extracts and their effects on germination of selected parasitic Orobanchaceae weeds

Abstract

Extracts of Euphorbia Eaegyptiaca (fresh and dry shoots and latex) were assessed for ability to induce germination of seeds of selected root parasitic weeds (Striga hermonthica sorghum and millet strains, Orobanche crenata and Phelipanche ramosa). The seeds were then used to probe the chromatographic behavior of the active substances in an endeavour to develop cleanup protocols for the active compounds as prelude for further work on elucidation of structures and synthesis of analogues and/or mimics. E. aegyptiaca shoot (dry or fresh) and latex were extracted by a series of organic solvents, hexane, chloroform and ethylacetate, chosen on differential polarity. GR24 (a synthetic germination stimulant) and distilled water were used as positive and negative controls, respectively. The aqueous control induced negligible germination (0-1%) while GR24 effected 93% germination of S. hermonthica, irrespective of strain. Achieved seed germination results ranging of Hexane, chloroform, ethanol, butanol and ethylacetate extracts of dry E. aegyptiaca dry shoots induced 44%, 86%, 87%, 93% and 88% germination of S. hermonthica strain. The corresponding germination of the pearl millet congener were 35%, 87%, 59%, 21% and 67%. P. ramosa displayed 0, 33, 5, 5 and 13% germination when challenged the extracts as above. O. crenata on the other hand displayed no germination these results explain the polarity behavior of germination stimulants. Thin layer chromatography (TLC) using a mixture of ethyl acetate and hexane (7:3) as a developing solvent showed two active spots at Rf 0.14 and 0.29. Using equi-volume (1:1) of hexane: ethyl acetate did not affect further separation. On column chromatography two active fractions were identified. Further analysis using LC-MS showed no peak or a mass dsdssspectrum corresponding to 5-deoxystrigol, strigol, strigylacetate, orobanchol, orobanchulacetate, sorgomol and sorgolactone. Lack of a ,m 7/mass spectrum corresponding to any of the aforementioned strigolactones (SLs) despite the detectable germination inducing activity suggest that the active ingredient(s) may be a novel SL, a non-SL compound or that the amount of the specific SL(s) is below the detection limits. It is noteworthy that bioassay using parasitic weed seeds are reported to be more than 100 times sensitive to SLs than instrumental analyses.