Horizontal natural product transfer: A so far unconsidered source of contamination of medicinal plants

Abstract

In this treatise, an actual overview on the newly verbalised phenomenon of "Horizontal Natural Product Transfer" is presented. This phenomenon was recently discovered when analyzing the potential sources of contaminations of plant derived commodities by nicotine and pyrrolizidine alkaloids. It turned out that these alkaloids, leached out from decomposing alkaloid containing plant parts (donor plants), are taken up by the roots of acceptor plants. In analogy to the well-known and widespread phenomenon of the uptake of xenobiotics, it can be deduced that a wide array of alkaloids and other natural products are taken up by acceptor plants either. As such uptake generally is due to a simple diffusion of the substances across the biomembranes, the physico-chemical properties of the natural products, especially their hydrophilic as well as their lipophilic character, determines the extent of a corresponding uptake. Latest findings from co-cultivation experiments revealed that natural products are not transferred exclusively from dead and rotting donor plant material, but also from living and vital plants. Yet, up to now, the exact path, i.e., in which manner the natural products are translocated from the living plants into the acceptor plants is unknown. The finding that plants inherently are able to take up most alkaloids from the soil, derived from other plants, necessitates a reconsideration of our understanding of plant-plant-interactions. In this context, also the classical definition of xenobiotics, which up to now are considered as "non-natural" substances, might be extended by including also natural products leached out into the soil.