Physiological and chemical activities of parthenin and other sesquiterpene lactones

Parthenium hysterophorus is an important weed in the Caribbean and, more recently, in India and Australia. The importance of this composite as a medical hazard and agricultural pest is reviewed. The sesquiterpene lactone, parthenin, which occurs in the trichomes of leaves and stems, is responsible for an epidemic of allergic contact dermatitis in India. My study is concerned with certain chemical and biological properties of this pseudoguaianolide as well as those of a number of other sesquiterpene lactones. Adducts of parthenin and cysteine were prepared and identified by is and NMR spectrometry. Formation of these adducts was affected by temperature and cysteine concentrations. It was found that both active sites of parthenin are responsible for its biological activities. The cyclopentenone moiety appears to be responsible for antimicrobial activity while the α-methylene-γ-lactone moiety seems to be responsible for toxicity and allergenicity. Feeding experiments with alantolactone showed that this compound is a feeding deterrent and that it also has detrimental effects on the flour beetle, Tribolium confusum. The application of parthenin on hearts of grasshoppers, Melanoplus sanquinipes, resulted in inhibition of myocardic activities. These findings support the view that plants have evolved the production of sesquiterpene lactones as a means of their defence against herbivorous predators.Science, Faculty ofBotany, Department ofGraduat