Chemical armament: Plants strengthen their defense with a chemical club

PPlants often use toxins to protect themselves from hungry mouths. These substances, which include caffeine and nicotine as well as the glycosides of the foxglove and the alkaloids of the opium poppy, usually come from our own production. Haller’s foam cress is one of the plants that instead extract toxic heavy metals from the ground (Arabidopsis states). Unlike the related thale cress (Arabidopsis thaliana), the preferred research object of geneticists, it forms offshoots on which – similar to strawberries – new plants grow. Instead of reproducing sexually, it can reproduce as a clone.

When Haller’s cress is nibbled, it sends its roots to places that are rich in cadmium and absorbs considerable amounts of the toxic heavy metal from the soil. The plants then not only arm their leaves, but also pass on the metal via their runners, as botanists from the University of Tübingen have discovered. In the greenhouse, Anubhav Mohiley and his colleagues each placed two plants connected by runners – that is, genetically identical – plants in different flower pots: One pot contained normal soil with a low cadmium content, the other the soil was enriched with the heavy metal.

No wonder that the cress thrive there poorly, after all, the metal also damages the plant metabolism. These plants kept the cadmium content of their leaves at just as moderate a level as their twins, who obtained water and nutrients from uncontaminated soil.

Experiment in the flower pot: potting soil with a low cadmium content on the left, with a high cadmium content on the right

Bild: Proceedings of the Royal Society B, Mohiley et al.

With chemical armament against parasites

To simulate an attack by hungry insects, the researchers poked holes in the leaves and applied jasmonic acid. This is a plant hormone that, among other things, encourages the defense against attackers. The connected potted plants reacted with chemical armament: Both tripled the cadmium content of their leaves.

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