| dc.description.abstracteng | Secondary metabolites can contribute to the plant’s survival in the ecosystem in various ways. They include allelochemicals involved in interactions with microorganisms, herbivores, and other plants sharing the same ecological niche.
Plenty of research reported the biological activity of allelochemicals in vitro, but only a few studies have proved the allelopathy in natural settings. Therefore, to mimic nature, we extracted secondary metabolites from the apoplast of the intact plant parts using water, which is the only solvent available in the environment. Furthermore, we applied numerous bioassays and sophisticated techniques to investigate the biological activity of the isolated secondary metabolites.
We characterized secondary metabolites in the bulbs of Galanthus nivalis and the metabolites secreted by the bulbs and roots into the soil. We revealed that Amaryllidaceae alkaloids secreted into soil strongly affect gram-negative soil bacteria, as shown by quantifying major groups of soil bacteria by taxon-specific real-time PCR and by sequencing amplified bacterial rRNA genes. On the other hand, non-secreted bulb metabolites did not affect bacteria and fungi but are toxic to invertebrates, suggesting that they may confer protection against soil-dwelling herbivores. On the other hand, one of the investigated alkaloids (TBH) showed strong phytotoxicity against Lemna minor.
Furthermore, we found that coumarins were involved in the phytotoxicity of the aqueous extract of Melilotus albus. We proved that the phytotoxic coumarins were released from living plants into the environment through root exudates and leaf leachates. We suggested that the coumarins released from M. albus debris may contribute to the suppressiveness of weeds germination in the surrounding area. We also suggested that the presence of coumarins in root exudate might play an ecological role by modulating the rhizosphere to make it favorable for Rhizobia nodules initiation by inhibiting the antagonists. However, these speculations need to be proved through further experiments.
Apart from the direct ecological functions, secondary metabolites provide a vast source of lead structures for therapeutic agents to humankind. For example, fumigation with heated henbane (Hyoscyamus niger) seeds has been used in folk medicine since the time of the ancient Egyptians. In our study, we proved the nematicidal activity of the fume released from heated henbane seeds, and we characterized the potential toxic volatiles. Among the target metabolites, mixtures of toxic aldehydes that could have been formed during the heating process, mainly α, β-unsaturated aldehydes, were identified. | de |