The phytotoxic lichen metabolite, usnic acid, is a potent inhibitor of plant p-hydroxyphenylpyruvate dioxygenase |
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Authors: | Romagni J G Meazza G Nanayakkara N P Dayan F E |
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Affiliation: | USDA/ARS, Natural Products Utilization Research Unit, University of Mississippi, Lafayette Co 38677, USA. romagnj@stthom.edu |
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Abstract: | The lichen secondary metabolite usnic acid exists as a (−) and a (+) enantiomer, indicating a or β projection of the methyl group at position 9b, respectively. (−)-Usnic caused a dose-dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (−)-Usnic acid inhibited protophorphyrinogen oxidase activity (I50=3 μM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase by (−)-usnic acid (apparent IC50=50 nM). |
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Keywords: | Bleaching herbicide Lichen p-Hydroxyphenylpyruvate dioxygenase Phytotoxin Alectoria sarmentosa |
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