Most studies conducted to test the allelopathic activity of plant parts have made use of water as solvent. However, the presence of polar, water-soluble substances, such as proteins and carbohydrates, tends to hamper the purification of active compounds. In this study, we present a simple purification procedure that separates the active fraction of the extract from the undesirable substances, thus facilitating the search for active molecules through standard chromatographic methods. Aqueous leaf extracts of three Cerrado species (Caryocar brasiliense, Qualea parviflora and Eugenia dysenterica) were prepared at 5% concentration (w/v) and stored at 4ºC (crude extracts). After 24 h, these solutions were filtered and freeze-dried. The powder obtained was dissolved in methanol, filtered again, evaporated and dissolved in water for bioassays (purified extracts). For the bioassays, seedlings of Sesamum indicum were grown for five days in aqueous solutions prepared from crude and purified extracts at concentrations ranging from 0.1% to 1.0% (w/v). Seedling growth in distilled water was set as a control. In comparison with the control, we found that test solutions prepared from both crude and purified extracts significantly inhibited sesame seedling growth. However, solutions prepared from purified extracts were two to ten times more inhibitory to seedling growth than were those prepared from crude extracts. The inhibition of root growth ranged from 35% to 77%, depending on the plant species, at a concentration as low as 0.1%. Roots were more affected than were shoots. The effects of purified extracts on seedling morphology were similar to those observed when crude extracts were employed, indicating that the procedure of purification of crude extracts did not interfere with the mode of action of the active substances
allelopathy; cerrado; freeze-drying; leaf extract; purification
