Caprolactam, an Inhibitory Allelochemical Exuded from Germinating Buckwheat (Fagopyrum esculentum) Seeds

Abstract

An allelochemical, which showed an inhibiting activity against the radicle growth of cress seeds, was isolated from the exudates of germinating buckwheat seeds. It was identified as caprolactam based on its 1 H and 13 C NMR spectra. The occurrence of caprolactam in the exudates from seeds of various plant species was studied on the basis of HPLC retention time and its UV spectrum. Caprolactam was detected in the exudates from seeds of sunflower as well as buckwheat, but not in those from seeds of cress, rice, pea, lettuce and radish. The mode of exudation of caprolactam from buckwheat seeds into the culture solution, was studied in relation to seed germination. About 0.8 μg of caprolactam was found in a dry seed. Upon water imbibition for 1 day about 15 % of caprolactam was exuded into the culture solution. The content of caprolactam in an imbibed seed was about 0.69 μg. These results suggest that caprolactam, already presents in dry seeds, was exuded from the seeds into the environment during seed germination stage. Caprolactam inhibited the radicle growth of cress seeds at the concentrations higher than 3 mg/L. All these results suggest that caprolactam may play as an allelochemical in the inhibitory allelopathy of buckwheat seeds during seed germination stage.