|NANAYAKKARA, DHAMMIKA - University Of Mississippi|
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2012
Publication Date: 1/13/2013
Citation: Owens, D.K., Nanayakkara, D.N., Dayan, F.E. 2013. In planta mechanism of action of leptospermone: Impact of its physico-chemical properties on uptake, translocation, and metabolism. Journal of Chemical Ecology. 39:262-270.
Interpretive Summary: A number of essential oils are used to as contact burn-down herbicides in organic agriculture. In contrast, manuka oil has good premergence activity previous data suggested that this essential oil acted in a more systemic manner. We report that leptospermone is readily absorbed by roots and transported to the foliage where it can exert its herbicidal activity. A detail study of the structural properties of leptospermone was used to explain some of its behavior in plants.
Technical Abstract: Leptospermone is a natural ß-triketone that specifically inhibits the enzyme p-hydrophyphenylpyruvate dioxygenase, the same molecular target site as that of the commercial herbicide mesotrione. The ß-triketone-rich essential oil of Leptospermum scoparium has both preemergence or postemergence herbicidal activity, resulting in the bleaching of the treated plants and dramatic growth reduction. Radiolabeled leptospermone was synthesized to investigate the in planta mechanism of action of this natural herbicide. Approximately 50% of the absorbed leptospermone is translocated to the foliage suggesting rapid acropetal movement of the molecule. On the other hand, very little leptospermone was translocated away from the point of application on the foliage, indicating poor phloem mobility. These observations are consistent with the physico-chemical properties, such as the experimentally measured logP and pKa, and the molecular mass, number of hydrogen donors and acceptors and the number of rotatable bonds. Consequently, it is readily taken up by roots and translocated to the reach its molecular target site. This provides additional evidence that the anecdotal observation of allelopathic suppression of plant growth under ß-triketone-producing species may be due to the release of these phytotoxins in soils.