A complex pattern of changes in the free amino acid composition of the eluate from germinating seeds of Glycine wightii was observed using a stepped platform apparatus. The growth of lettuce fruits was strongly inhibited by the eluate from Glycine wightii seedlings. INTRODUCTION It has been suggested that one of the roles for secondary metabolites in plants may be to inhibit the germination or growth of competing species (Bell, 1976; Seigler, 1977). It has been shown that several non-protein amino acids isolated from plants are growth inhibitors of plants which do not contain them (Fowden, 1963; Wilson and Bell, 1978). Seeds of Glycine wightii are rich in the non-protein amino acid canavanine (Lackey, Isley, and Palmer, 1974), a structural analogue of arginine, which has been shown to inhibit the growth of certain plant species (Weaks and Hunt, 1973, 1974), including lettuce (Wilson and Bell, 1978). In the seeds of Glycine wightii we have also detected high concentrations of a second, unidentified ninhydrin-reacting compound. This compound, reported here for the first time, has also been isolated, but as we have not yet determined its structure we designate it GW1. In ungerminated seeds, canavanine and GW1 are the two major components of the free amino acid pool. We have devised a method for determining the changes in the free amino acid content of the eluate from germinating seeds of Glycine wightii, and have attempted to relate the amino acid content of the eluate to its effect on the growth of lettuce seedlings. This content downloaded from 157.55.39.100 on Thu, 25 Aug 2016 06:22:31 UTC All use subject to http://about.jstor.org/terms 1244 Wilson and Bell—Composition of Seedling Eluates MATERIALS AND METHODS Changes in free amino acid content A perspex, stepped platform was constructed as shown in Fig. 1 and Whatman 17 chroma paper cut to the appropriate size to dip into the upper reservoir and follow the contours down to the base. The paper was cut to a point to allow fractions to be collected. Five hundred seeds of Glycine wightii, which had previously been surface-sterilized with 5% (w/v) sodium hypochlorite solution, were sown on step B (Fig. 1) and covered with an inverted Petri dish to maintain high humidity and grown under continuous illumination. The flow rate was determined as 4 ml h_1 and the apparatus kept at 25 °C. Fractions were collected at 5 h intervals,