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JXB Advance Access originally published online on April 8, 2009
Journal of Experimental Botany 2009 60(7):2107-2117; doi:10.1093/jxb/erp082
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Dynamic root exudation of sorgoleone and its in planta mechanism of action

Franck E. Dayan1,*, J'Lynn Howell1 and Jeffrey D. Weidenhamer2

1United States Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, University, MS 38677, USA
2Department of Chemistry, Ashland University, Ashland, OH 44805, USA

* To whom correspondence should be addressed. E-mail: fdayan{at}olemiss.edu

The oily droplets exuded from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analogue. The production of these droplets appears to be suppressed when c. 20 µg of exudate mg–1 root dry weight accumulates at the tip of the root hairs. However, more exudate is produced following gentle washing of the roots with water, suggesting that the biosynthesis of lipid benzoquinones and resorcinols is a dynamic process. Sorgoleone interferes with several molecular target sites, including photosynthetic electron transport, in in vitro assays. However, the in planta mechanism of action of sorgoleone remains controversial because it is not clear whether this lipid benzoquinone exuding from the roots of sorghum is taken up by roots of the receiving plants and translocated to their foliage where it must enter the chloroplast and inhibit PSII in the thylakoid membrane. Experiments designed to test the in planta mode of action of sorgoleone demonstrated that it has no effect on the photosynthesis of older plants, but inhibits photosynthesis in germinating seedlings. Sorgoleone is not translocated acropetally in older plants, but can be absorbed through the hypocotyl and cotyledonary tissues. Therefore, the mode of action of sorgoleone may be the result of inhibition of photosynthesis in young seedlings in concert with inhibition of its other molecular target sites in older plants.

Key words: Allelochemical, allelopathy, lipid resorcinols, mode of action, sorghum, sorgoleone

Received 7 January 2009; Revised 20 February 2009 Accepted 27 February 2009


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