Leaching of the allelopathic substance, L-tryptophan from the foliage of mesquite (Prosopis juliflora (Sw.) DC.) plants by water spraying

The allelopathic potential of L-tryptophan in the leachate from the foliage of mesquite ( Prosopis juliflora (Sw.) DC.) plants was investigated. Distilled water (500 ml) was sprayed on mesquite plants from above for 50 min and water passing through the foliage was collected. The content of L-tryptophan in the sample ( 30 ml eq.) was analyzed using a physicochemical method and the concentration was shown to be 17.9 muM. The sample ( 30 ml eq.) caused 69.8% inhibition of the root growth of barnyard grass ( Echinochloa crus-galli L.). The concentration of authentic L-tryptophan required for 69.8% inhibition of the root growth of barnyard grass was estimated at 20.0 muM from the dose-response curve. Moreover, to establish the origin of L-tryptophan in the leachate, the amount of L-tryptophan in both the leaves and the leachates was determined. The amount of L-tryptophan containing in the foliage significantly decreased by soaking with time, whereas in the leachates the amount increased. After 60 min, its content in the leachates was nearly equivalent to that of the leaves. These results suggest that L-tryptophan leached from the foliage may play an important role in the allelopathy imposed by mesquite.