An edible lily plant, one of the most important vegetables grown in Hokkaido, Japan, is often threatened by a a fungus that develops lesions in the bulbs. But the stress caused by the attack of the plant pathogen triggers a series of chemical reactions that causes the plant to make some natural pesticides, according to a research group led by Kenji Monde of Hokkaido University. Their results appear in the June 13 Web edition of the Journal of Natural Products, a joint publication of the American Chemical Society and the American Society of Pharmacognosy.
Monde's group was struck by the fact that bulb lesions were limited to the outermost scales, which suggested a "dynamic resistance of the plant to the invading pathogens." Meticulously piecing together the series of chemical events, the Hokkaido group found that the plant made these new pesticides by chlorination of a compound called orcinol, which occurs naturally in the plant. Seven chlorine-containing orcinol derivatives were found, and six showed significant antifungal activity. Although organochlorine compounds have been found in a variety of marine organisms, they are rarely found in terrestrial higher plants.
Monde says that they carefully ruled out fungal or microbial origins of these chlorine compounds, and he is convinced that only the lily plant is responsible for making these compounds to defend itself from attack. These natural organochlorine pesticides are very unstable. This natural tendency to breakdown gives them an inherent advantage over synthetic organochlorine pesticides which persist for a long time and have resulted in many environmental problems.
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