Science - October 31, 2012

Plant gives offspring organic pesticide

The seeds of Pyrethrum, a daisy-like flower, get compounds from the parent plant that protect them against soil fungi and insects. The plant produces the organic pesticide in its trichomes.

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These findings were reported this month by Wageningen plant physiologists and entomologists in Plant Cell. The discovery gives new insights in how plants function.
Pyrethrum produces the protective compounds, pyrethrins, in the trichomes on the outside of the seeds. They are also found on the plant's leaves and stalks. Pyrethrins have been used as an organic insecticide for a century. Researchers had always thought that the compounds merely formed a line of defence around the plant's exterior.
But now it turns out that the trichomes also transport compounds inside the plant. The Wageningen scientists discovered that these are monoterpenes that the plant converts into pyrethrins.  These protective compounds are absorbed in the embryo and passed on when the seeds germinate. In this way, the parent plant makes sure the offspring have plenty of pyrethrins that protect the seedlings in their early life against fungi and damaging insects.
In addition, the trichomes of the offspring also play their familiar part in the production of other pesticides for the plant. For example, they hinder the root growth of rival plants, giving Pyrethrum the advantage in the germination phase.
Now that the researchers have figured out the biosynthesis of the protective compounds, they think they will be able to create other compounds in seeds in the same manner. That could result in more or different natural pesticides, for example. The research was carried out under the auspices of the TTI Green Genetics. Two plant breeding companies contributed to the costs of the research. 

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