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ARS Home » Southeast Area » Oxford, Mississippi » Natural Products Utilization Research » Research » Publications at this Location » Publication #236064
Title: Dynamic Root Exudation of Sorgoleone and Its in Planta Mechanism of Action

Author
item Dayan, Franck
item Howell, J Lynn
item WEIDENHAMER, JEFFREY - ASHLAND UNIVERSITY-OHIO

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2009
Publication Date: 4/8/2009
Citation: Dayan, F.E., Howell, J., Weidenhamer, J. 2009. Dynamic Root Exudation of Sorgoleone and Its in Planta Mechanism of Action. Journal of Experimental Botany. 60(7):2107-2117.

Interpretive Summary: The oily droplets exuding from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analog. The production and release appear to be suppressed when 15 to 20 µg/mg 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 inhibition of 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.

Technical Abstract: The oily droplets exuding from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analog. The production and release appear to be suppressed when 15 to 20 µg/mg 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 inhibition of 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.