Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/2/2003
Publication Date: 11/5/2003
Citation: KAGAN, I., RIMANDO, A.M., DAYAN, F.E. CHROMATOGRAPHIC SEPARATION AND IN VITRO ACTIVITY OF SORGOLEONE CONGENERS FROM THE ROOTS OF SORGHUM BICOLOR. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2003. V. 51(26). P. 7589-7595. Interpretive Summary: The presence of sorghum (Sorghum bicolor) in a field can reduce growth of weeds and other plants. This allelopathic (plant growth inhibiting) property is partly due to sorgoleone, the most abundant component of the oily substance exuded from sorghum root hairs. The phytotoxicity of sorgoleone has been shown to be due to inhibition of photosynthesis. The root exudate also contains small amounts of sorgoleone analogues, differing only in the number of carbons or double bonds in the side chain. This research has led to the isolation and structural characterization of the sorgoleone analogues, using column chromatographic and argentation chromatographic techniques. Their inhibitory activity on photosynthesis was found to be similar to that of sorgoleone, suggesting that all of these analogues contribute to the overall allelopathic potential of sorghum. The ability to obtain these minor compounds in large enough quantities to use as pure standards will facilitate studying their role in nature.
Technical Abstract: Sorgoleone, 2-hydroxy-5-methoxy-3-[(8'Z, 11'Z)-8',11',14'-pentadecatriene]-p-benzoquinone (1), and its corresponding hydroquinone are the major components of the root exudate of Sorghum bicolor. The name sorgoleone includes minor analogues differing in the length or degree of unsaturation of the 3-alkyl side chain. These compounds are known to be phytotoxic, probably through inhibition of Photosystem II driven oxygen evolution, as previously demonstrated for 1. Scaled-up isolation of these sorgoleone congeners was achieved by C8 column chromatography and argentation thin-layer chromatography, and the purified compounds were structurally characterized. The abilities of the minor sorgoleones to inhibit Photosystem II were compared to that of the major compound.