Effect of isoalantolactone on germination, biomass production and respiration of young seedlings

Isoalantolactone, a sesquiterpene lactone occurring in many composites, significantly reduced the germination and biomass production of two weed species, Amaranthus retroflexus L. (redroot pigweed) and Chenopodium album L. (lamb's-quarters), but had no effect on seeds of lettuce and wheat. Respiration of the seedlings of both weeds was significantly affected by isoalantolactone. In pigweed, 10 mu g/ml and 20-250 mu g/ml of the lactone stimulated respiration for the first 24 h but after 48 and 72 h the larger amounts had inhibitory effects. In lamb's-quarters, isoalantolactone generally stimulated the respiration of seedlings. The respiration of wheat and lettuce was not affected by the lactone treatment.