Naphthaleneacetic acid suppresses peroxidase activity during the induction of adventitious roots in soybean hypocotyls

The synthetic auxin naphthaleneacetic acid (NAA) promoted rooting in soybean (Glycine max) hypocotyls. The activity of anionic peroxidases (PODs, pI 3.5, pI 3.7 and pI 4.4) and cationic PODs (pI 8.3, pI 9.1 and pI 9.4) was significantly inhibited by exogenous NAA during the induction of adventitious roots. In addition, the reduction in POD activity (pI 4.4, pI 8.3 and pI 9.4) correlated with a reduction in corresponding transcription activity. POD patterns and transcription in NAA-treated hypocotyls demonstrated the specific effect of NAA on POD isozymes, indicating that NAA suppresses POD gene expression during the induction of adventitious root. The decline of POD activity in NAA-treated hypocotyls was accompanied by a decrease in lignin content. We suggest that both anionic and cationic PODs might be involved in lignin synthesis in soybean hypocotyls.