ABSTRACT
Allelopathic interactions are mediated by secondary metabolites released from donor plants to the environment and have an influence on the growth and development in both natural and agro-ecosystems. These allelochemicals belong to many chemical groups and have different sites and modes of biochemical action. In general, when the effect of these allelochemicals decreases the growth of the receiver plant, it is considered as a biotic stress called allelochemical stress'. This environmental stress factor can act as a mechanism of interference and can influence the pattern of vegetation, weed growth and crop productivity (Dakshinief al. 1999; Weiref al 2004; Romero-Romero et al. 2005). Allelochemicals can have several molecular targets in the receiver plants, interfering with different cellular processes and thus inhibiting plant growth. Previous studies have shown that allelochemical stress can cause an (i) oxidative damage [evidenced by an increase in reactive oxygen species (ROS)] to membranes and (ii) modification in some antioxidant enzyme activities (Cruz-Ortegaef al 2002; Bais et al 2003; Weir et al 2004).
