Allelopathic interactions between plants. Multi site action of allelochemicals

Allelopathy is defined as mechanism of plant-plant, plant-microorganisms, plant-virus, plant-insect, and plant-soil-plant interactions mediated by plant- or microorganism-produced chemicals released to the environment. The majority of allelochemicals are secondary metabolites and among others belong to terpenoids, phenolic compounds, organic cyanides and longchain fatty acids. The action of allelochemicals in target plant is diverse and affects a large number of biochemical reactions resulting in modifications of different physiological functions. Thus the results of allelochemical action can be detected at different levels of plant organization: molecular, structural, biochemical, physiological and ecological. Enzyme activities, cell division and ultrastructure, membrane permeability, ion uptake and as a consequence plant growth and development are modified by allelochemicals. Significant effects on photosynthesis and respiration are the best-characterized results of allelopathic interactions. Moreover allelopathic compounds seem to induce a secondary oxidative stress expressed as enhanced free radical production and induction of cellular antioxidant system. Plant survival under allelopathy stress conditions depends on plant defense leading to allelochemical detoxication, the process which may go on in parallel to cell defense reaction to oxidative stress. The article presents some aspects of the current knowledge regarding mechanisms of the allelopathy phenomenon. The allelopathy is a complex problem, thus comprehensive understanding of allelochemical mode of action requires further investigation and still remains an open question.