Stimulation of Striga hermonthica seed germination by 11β,13-dihydroparthenolide

Germination tests of Striga hermonthica seeds were performed using 11 beta,13-dihydroparthenolide (DHP), a sesquiterpene lactone from Ambrosia artemisifolia (common ragweed). In each test series aqueous solutions with acetone or methanol were used as negative controls. Test solutions of the strigol analogue 2-methyl-4-((2-oxo-2,3,3a,8b-tetrahydro-4H-indeno[1,2-b]furan-3-ylidene)methoxy)-but-2-en-4-olide (GR 24) in methanol as carrier system were used as positive controls. A decrease in concentration of DHP from 10(-3) to 10(-20) M resulted in several unusual "minima" and "maxima" of stimulatory activities, suggesting that the mode of action of DHP could be hormonal. The crystal structure of DHP was determined by X-ray crystallography, and the use of molecular modeling in predicting the biologically active conformations is proposed.