The acute effect of copper on the levels of indole-3-acetic acid and lignin in peanut roots

Cu-treated peanut (Arachis hypogaea L.) seedlings showed a significant inhibition in peanut root growth, and a decrease in endogenous indole-3-acetic acid (IAA) content. The decline of IAA content in Cu-treated tissue was accompanied by an increase in the activity of cationic peroxidase (POD) isozyme P8.5, which was correlated with an increase in cationic POD transcripts. Cu might suppress the growth of peanut roots by inducing the synthesis of the cationic POD isozyme that degrades endogenous IAA. The increase in the activity of anionic POD isozyme P3.5 was correlated with the rise in lignin content in Cu-treated roots. We suggest that the increase in anionic POD isozyme P3.5 induced by Cu might be responsible for lignin synthesis in peanut roots, and may also remove excess hydrogen peroxide caused by Cu, thus playing a detoxifying role during Cu treatment.