Rapid effect of cadmium on lignin biosynthesis in soybean roots

The significant root inhibition growth in Cd-treated soybean (Glycine max) seedlings correlated with the increase of H2O2 levels, peroxidases and laccases activity. The increased peroxidase activity might remove excess H2O2 as the incubation was prolonged during Cd treatment, thus playing a detoxifying role. The increase of the activities of peroxidase (pI 8.8, pI 7.7, pI 5.2, pI 4.5, pI 4.4, and pI 3.7) and laccase (pI 9.2, pI 8.9, pI 8.3, pI 5.4, pI 4.2, and pI 3.7) were accompanied by the rise of lignin contents in Cd-treated tissues. In Cd-treated root tips, transcript levels of POXs (pI 7.7, pI 5.2, pI 4.5, pI 4.4, and pI 3.7 POXs) increased significantly compared with the controls after 48 h of treatment. Our results suggest that laccases are responsible for lignin biosynthesis during the early stage of Cd treatment. Laccases and peroxidases worked cooperatively in lignin synthesis when the treatment was prolonged.