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Abstract: Psychotria leiocarpa is an understorey woody shrub native to the forests of southern Brazil, which occurs in groups of relatively high density. Leaves of field-grown plants contain approximately 2.5% of their dry weight as the N-glycosylated indolic alkaloid N,β-d-glucopyranosyl vincosamide (GPV). To find out if allelopathy could play a role in the distribution pattern of the species, several assays were performed. Aqueous extracts of dried powdered leaves at 4% (w/v) collected during the winter of 2004 inhibited the germination and/or early growth of three different test species. Lactuca sativa plantlets were affected when grown in soil containing dried P. leiocarpa leaves and on plates containing aqueous extracts of leaves of the same species. Partial chemical characterization of the extract was carried out and an allelopathic effect of the purified major leaf alkaloid GPV was not observed at the highest concentration tested of 10 ppm. Experiments with different organic extracts and sequential extractions were also performed. The data suggested that polar phenolic compounds or iridoids are responsible for the phytotoxic effect observed. [Copyright &y& Elsevier]

Abstract: In South Brazilian grasslands, the shrubs Heterothalamus psiadioides Less and Baccharis patens Baker show a dominance pattern that may be a consequence of allelopathy. In this study, the phytotoxic effects of H. psiadioides and B. patens and the seasonal variation in these effects were assessed. The effects of the volatiles released directly from fresh and dry leaves of the both species were evaluated on germination and growth of the target plants lettuce and onion in four seasons. The volatiles from H. psiadioides and B. patens inhibited the germination rate and speed of germination and reduced the shoot and root length of the target plants, with fresh leaves showing greater phytotoxicity. These parameters were more affected by H. psiadioides than by B. patens in all seasons and both plants showed a decrease in phytotoxicity in summer. It can be concluded that both shrubs possess allelopathic potential, with H. psiadioides showing stronger effects. Interseasonal variation of phytotoxicity should be taken into account in studies of potentially allelopathic plants. [Copyright &y& Elsevier]

Abstract: Schinus lentiscifolius March. essential oil was obtained by hydrodistillation of the leaves, and its compounds were tentatively identified using a gas chromatograph coupled to a mass spectrometer detector and a gas chromatograph with a flame ionization detector. Chromatographic analyses showed that this essential oil is a complex mixture of terpenes and that the most abundant chemicals were sesquiterpene hydrocarbons (41.52%), with δ-cadinene (14.43%) as the major compound. Phytotoxicity testing assays using this essential oil showed a decrease in the percent of germination, the speed of accumulated germination, and root and shoot length in onion and lettuce. The effects of volatiles on the mitotic processes of target species' root meristems were also evaluated. Compared to the negative control, S. lentiscifolius essential oil reduced the mitotic index of onion by 19.35% and that of lettuce by 25.14%. Essential oil also induced aneugenic and clastogenic effects on the root meristems of target species, promoting the occurrence of micronuclei and stickiness. [Copyright &y& Elsevier]