Allelopathy Journal

We investigated the effects of application of juglone on the growth and cell viability, the activities of phenylalanine ammonia-lyase (PAL) and soluble and cell wall-bound peroxidase (POD), as well as the lignin content and its monomeric composition in the roots of soybean (Glycine max L. Merrill). Three-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0), with or without 5 μM juglone in a growth chamber (25°C, 12/12 h light/dark photoperiod, irradiance of 280 μmol m⁻² s⁻¹) for 24 h. After juglone exposure, the root length and the fresh and dry weights decreased drastically, followed by major loss in cell viability. The soluble and cell wall-bound POD activities decreased, while PAL activity significantly increased just after juglone exposure. Thus juglone increased the lignin content and its p-hydroxyphenyl (H) monomer in the roots of soybean seedlings. These results suggested that the exogenous application of juglone allelochemical induced the inhibition of root growth in soybean due to excessive production of lignin.