Plant growth inhibitory activity of p-hydroxyacetophenones and tremetones from Chilean endemic Baccharis species and some analogous:: A comparative study

Plant growth inhibitory effects of acetophenones 1-6, tremetones 7-12, and MeOH and CH2Cl2 extracts from the aerial parts of Baccharis linnearis, Baccharis magellanica, and Baccharis umbelliformis collected in Chile were assayed as growth inhibitory activity in ranges of 10-500 muM and 0.1-150 ppm, respectively. The effects on seedling growth, germination, and respiration of ryegrass, lettuce, green tomato, and red clover weedy target species were measured. In addition to the inhibitory activity on bleaching of crocin induced by alkoxyl radicals, these compounds also demonstrated scavenging properties toward 2,2-diphenyl-1-picrylhydrazyl in thin-layer chromatography autographic and spectrophotometric assays. In addition, acetophenones and tremetones also showed inhibition of H+ uptake and oxygen uptake respiration in isolated chioroplasts and mitochondria, respectively. Our results indicate that 1, 4, 7-12, and CH2Cl2 extracts interfere with the dicot preemergence properties, mainly energy metabolism of the seeds at the level of respiration. These compounds appear to have selective effects on the radicle more than shoot growth of dicot seeds. Also, the levels of radicle, inhibition obtained with some compounds on Physalis ixocarpa and Trifolium pratense are totally comparable to those of ovatifoiin, a known natural growth inhibitor. This behavior might be responsible for its plant growth inhibitory properties and its possible role as an allelopathic agent.