When pea seeds were cultured in a Petri dish together with cress seeds, the hypocotyl and root growth of cress was significantly inhibited, whereas the epicotyl growth of pea was promoted. These results suggest that the growth of each seeds is either inhibited or promoted with allelochemical(s) exuded from each seeds during seed germination. An allelochemical, which showed a growth-inhibiting activity against cress seeds, was isolated from the exudates of germinating pea seeds. It was identified as 6a-hydroxy-3-methoxy-8,9-methylenedioxy peterocarpan (pisatin) based on its 1H NMR spectrum. The endogenous pisatin level (22 mg/L) in the exudates from germinating pea seeds seems to be a good agreement with the exogenous concentration (&gt
3 mg/L) of pisatin required to inhibit the hypocotyl and root growth of cress. These results suggest that pisatin may play an important role in the allelopathy of pea seeds during germination. © 2005 Japan Institute of Heterocyclic Chemistry.