Naringenin Inhibits the Growth and Stimulates the Lignification of Soybean Root

The flavanone naringenin, an intermediate in flavonoid biosynthesis, was tested for its effect on root growth, phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities, as well as phenolic compounds and lignin contents in soybean (Glycine max L. Merrill) seedlings. Three-day-old seedlings were cultivated in half-strength Hoagland nutrient solution (pH 6.0), with or without 0.1 to 0.4 mM naringenin in a growth chamber (25 degrees C, 12-h photoperiod, irradiance of 280 mu mol m(-2) s(-1)) for 24 h. Inhibitory effects on root growth (length, weight, cell viability), PAL and soluble POD activities were detected after naringenin treatments. These effects were associated with stimulatory activity of the cell wall-bound POD followed by an increase in the lignin contents, suggesting that naringenin-induced inhibition in soybean roots could be due to the lignification process.