If tobacco plants are in distress, they call for help with the help of fragrances. Image: William Rafti, wikipedia.org
Reading aloud Plants can communicate: If they are in distress, they call for help with the help of fragrances. At the same time they take special, tailored to the pest repellent measures. Researchers from Jena are deciphering this chemical language. In the future, this could potentially help make crops more resistant to pests. In the laboratory of the Jena Max Planck Institute for Chemical Ecology plants are tormented - with tweezers, razor blades, scissors and more recently with a small robot that mimics the chewing movements of a caterpillar. Behind this, however, are no sadistic inclinations, but the attempt to understand a phenomenon that has long been ignored: the secret cries for help from the plants.

For the green creatures are anything but mute, reports the magazine "Bild der wissenschaft" in its September issue. Rather, they have a whole arsenal of chemical vocabulary at their disposal to fend off enemies and call for help. How complex this system is, the researchers in Jena got very quickly in their laboratory torments: The tobacco plants that they dealt with razor blade and Co, responded namely not at all to the injuries - apparently because they realized that it is not the author Fressfeind acted, but to the equivalent of a hailstone or a gust of wind, against a complex defense reaction would make no sense.

It was different, however, when the scientists nibbled a robot named "MecWorm" on their plants. "MecWorm mimics the feeding process of an insect for hours, " explains Wilhelm Boland, head of the Institute of Bioorganic Chemistry. And indeed: The tobacco plants considered the artificial caterpillar a real danger and threw their emergency program - but still in the economy version. Only when the researchers additionally provided MecWorm with caterpillar saliva did the plantlets run their defensive machinery to full speed.

What follows is quite impressive: After five to ten minutes, the combination of saliva and feeding rhythm causes the entire leaf to release a hormone called jasmine. This serves as an internal alarm signal and in turn triggers a series of emergency chemical reactions. The first of these cry for help consists of so-called green leaf fragrances, which flow from the wound and spread over the wind for miles. display

After about an hour, the first genes in the plant are reprogrammed, and after about five hours, the production of toxins for defense can start - provided that it makes sense: The plant forms only toxic substances, if this the nibbling caterpillars something can affect. However, if a tobacco plant recognizes, for example, the saliva of a tobacco swarmer, it leaves the costly production the same, because its caterpillars are immune to the neurotoxin nicotine with which the plant would otherwise fight back.

Instead, it forms digestive proteins and a whole cocktail of perfumes. With that it has a very special purpose: they serve to summon allies. "Grown in place, plants had to learn in the course of evolution to effectively defend themselves, " explains the Jena plant scientist Ian Baldwin in "Bild der wissenschaft". "But why fight for yourself, when it's much cheaper and easier to let the other do it for you?"

Others are, for example, parasitic wasps, which deposit their eggs in the body of caterpillars. They learn at a relatively early stage which fragrances signal the presence of suitable host caterpillars on certain plants, and hurry to avoid the opportunity of oviposition. And that is exactly what the plant has in mind, because the wasp larvae eat the caterpillar from the inside and make it harmless.

However, there is a problem: not only the wasps smell the chemical cries for help and can interpret them correctly, even the enemies of plants are capable of doing so. As a result, the eye-catching traces of fragrance also endanger the plant's neighbors - who, however, react to this with increased defensive measures and upregulate certain genes at the first sign of danger.

If they do not succeed, they have bad maps, the Jena researchers have shown in a desert in the US state of Utah: tobacco plants that could no longer understand their neighbors due to a genetic change, so their signals could no longer be perceived, were uneven after a few days more infested with pests than their unidentified counterparts. The same was true of plants that researchers had the ability to communicate with.

Especially the latter is not only interesting for research: Due to the extreme breeding, many of today's crops such as tomatoes and cotton are chemically dumb and thus virtually helpless against insects. So, if man learns to understand the plant language, he may be able to teach these plants to communicate and ultimately reduce the use of pesticides, hopes plant scientist Baldwin.

Nadine Eckert: "The silent scream" in: bild der wissenschaft 9/2007, p. 14 ddp / science.de - Ilka Lehnen-Beyel

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