Contemporary analyses from co-cultivation experiments outlined that natural
products are not exclusively transferred from dead and rotting donor plant
material but also from living and vital plants. Moreover, the compounds imported
are modified within the acceptor plants.
In this chapter, an actual overview on the phenomenon of horizontal
natural product transfer is presented and its relevance for our understanding
of plant-plant-interactions is discussed. The fact that common natural
products are readily translocated from one plant into others will strongly change
our understanding of allelopathy. Up to now, in plant-plant interactions,
only “classical allelochemicals” had been taken into consideration, e.g., those
compounds that reveal certain and definite significance by inhibiting the growth
or the germination of potential competitors.
Keywords
Horizontal transfer · Natural products · Nicotine · Pyrrolizidine alkaloids ·
Xenobiotics · Alkaloids
1
Introduction
It is a matter of course that plants take up substances from the soil by the means
of their roots. Apart from inorganic nutrients, such as nitrate, phosphate, or various
metal ions, many other compounds are imported via the roots. Regarding chemical
ecology, the uptake of active compounds, denoted as allelochemicals, which inhibit
germination or growth of putative competitors, is of special interest [1]. In general,
these substances are exuded from donor plants and exhibit their effect on the plants
growing in their vicinity [2, 3]. Commonly, the allelochemicals are taken up by the
acceptor plants [1, 4]. A corresponding uptake of substances is well known
for xenobiotics, e.g., systemic herbicides and fungicides [5] or veterinary medicines
[6]. Furthermore, salicylic acid, which is responsible for systemic acquired resistance, is known to be imported by roots [7, 8].
When considering the uptake of substances by the roots, one substantial issue has
to be emphasized: whereas the import of most ionic nutrients like nitrate, sulfate,
or metal ions requires specific transporters [9–11], most of the xenobiotics are taken
up by just simple diffusion [5]. Due to their partially hydrophobic character, these
molecules are able to diffuse passively through membranes [12–14]. Although these
coherences were well established, corresponding reflections with respect to
common natural products had not been considered. The situation changed with
recent investigations, which were aimed to identify the potential sources of
various contaminations of plant-derived commodities with nicotine [15] and
pyrrolizidine alkaloids [16, 17]. Corresponding pot experiments [18] as well as
extensive field trials [19] demonstrated that nicotine, which is leached out from
dried tobacco plant material, i.e., discarded cigarette butts, is taken up massively by
acceptor plants. Analogously, pyrrolizidine alkaloids (PAs), which are leached out
from rotting PA containing weeds, e.g., Senecio jacobaea, are also taken up by
430
D. Selmar et al.
products are not exclusively transferred from dead and rotting donor plant
material but also from living and vital plants. Moreover, the compounds imported
are modified within the acceptor plants.
In this chapter, an actual overview on the phenomenon of horizontal
natural product transfer is presented and its relevance for our understanding
of plant-plant-interactions is discussed. The fact that common natural
products are readily translocated from one plant into others will strongly change
our understanding of allelopathy. Up to now, in plant-plant interactions,
only “classical allelochemicals” had been taken into consideration, e.g., those
compounds that reveal certain and definite significance by inhibiting the growth
or the germination of potential competitors.
Keywords
Horizontal transfer · Natural products · Nicotine · Pyrrolizidine alkaloids ·
Xenobiotics · Alkaloids
1
Introduction
It is a matter of course that plants take up substances from the soil by the means
of their roots. Apart from inorganic nutrients, such as nitrate, phosphate, or various
metal ions, many other compounds are imported via the roots. Regarding chemical
ecology, the uptake of active compounds, denoted as allelochemicals, which inhibit
germination or growth of putative competitors, is of special interest [1]. In general,
these substances are exuded from donor plants and exhibit their effect on the plants
growing in their vicinity [2, 3]. Commonly, the allelochemicals are taken up by the
acceptor plants [1, 4]. A corresponding uptake of substances is well known
for xenobiotics, e.g., systemic herbicides and fungicides [5] or veterinary medicines
[6]. Furthermore, salicylic acid, which is responsible for systemic acquired resistance, is known to be imported by roots [7, 8].
When considering the uptake of substances by the roots, one substantial issue has
to be emphasized: whereas the import of most ionic nutrients like nitrate, sulfate,
or metal ions requires specific transporters [9–11], most of the xenobiotics are taken
up by just simple diffusion [5]. Due to their partially hydrophobic character, these
molecules are able to diffuse passively through membranes [12–14]. Although these
coherences were well established, corresponding reflections with respect to
common natural products had not been considered. The situation changed with
recent investigations, which were aimed to identify the potential sources of
various contaminations of plant-derived commodities with nicotine [15] and
pyrrolizidine alkaloids [16, 17]. Corresponding pot experiments [18] as well as
extensive field trials [19] demonstrated that nicotine, which is leached out from
dried tobacco plant material, i.e., discarded cigarette butts, is taken up massively by
acceptor plants. Analogously, pyrrolizidine alkaloids (PAs), which are leached out
from rotting PA containing weeds, e.g., Senecio jacobaea, are also taken up by
430
D. Selmar et al.