Effects of ferulic acid on growth and lignification of conventional and glyphosate-resistant soybean

Ferulic acid (allelochemical commonly found in soil extracts) affects the root growth and lignification of soybean (Glycine max L. Merr.) seedlings. Glyphosateresistance is conferred in soybean by incorporating a gene encoding a glyphosateinsensitive enzyme (CP4-EPSP synthase), which acts in the shikimate pathway to synthesize aromatic amino acids and lignin. To evaluate the possible tolerance of glyphosate-resistant soybean to ferulic acid, comparative studies were done for its effects on the root growth and lignification of two soybean cultivars (conventional and glyphosate-resistant). Three-day-old seedlings of CD 201 (conventional soybean) and CD 214RR (glyphosate-resistant soybean) were cultivated in half-strength Hoagland nutrient solution (pH 6.0), with or without 1.0 mM ferulic acid, 0.5 mM glyphosate or a mixture of 1.0 mM ferulic acid plus 0.5 mM glyphosate in a growth chamber (25°C, 12 h/12 h light/dark photoperiod, irradiance of 280 μmol m⁻² s⁻¹, 24 to 96 h). The ferulic acid decreased the length, fresh weight and dry weight of roots of both cultivars. Root growth inhibition has been associated with an increase in lignin contents. The mixture of ferulic acid and glyphosate showed similar effects in both cultivars. These results confirm the susceptibility of both conventional and glyphosate-resistant seedlings to ferulic acid and suggest that the genetic modification in the glyphosate-resistant soybean does not develop tolerance to ferulic acid.