Lignin monomer composition in untreated (Control) soybean roots and roots treated with 1.0 mM <i>p</i>-coumaric acid (<i>p</i>-COU), 1.0 mM <i>p</i>-coumaric acid plus 0.1 mM piperonylic acid (<i>p</i>-COU+PIP) and 1.0 mM <i>p</i>-coumaric acid plus 2.0 mM 3,4-(methylenedioxy)cinnamic acid (<i>p</i>-COU+MDCA).

<p>Mean ± SE values (<i>N</i> = 4) followed by different letters are significantly different according to the Scott–Knott test (<i>P</i>≤0.05). H, <i>p</i>-hydroxyphenyl; G, guaiacyl; S, syringyl.