Roots of Sorghum Exude Hydrophobic Droplets Containing Biologically Active Components1

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Abstract
Roots of Sorghum are known to exude materials that exhibit allelochemical activity, but the compounds identified do not completely account for the observed species‐specific allelochemical activities. The purpose of this investigation was to characterize both water‐soluble and water‐insoluble exudates from roots of sorghum [Sorghum bicolor (L.) Moench] seedlings grown in petri dishes. Hydrophilic exudates included phenols, protein, and 3‐deoxyanthocyanidin derivatives. Hydrophobic droplets, exuded from root hairs, tested positively for phenols and lipids. These hydrophobic exudates strongly inhibit (85%) root elongation in lettuce (Lactuca sativa cv. Great Lakes) seedlings, but do not affect that of corn (Zea mays L. cv. B73Ht), nor the germination of either of these plants. Associated with these hydrophobic droplets are novel quinones, yet unidentified. The results indicate that these hydrophobic exudate droplets contain components that may have species‐specific biological activities.