Cytokinin modulates catalase activity and coumarin accumulation in in vitro cultures of tobacco

Cytokinins (CKs) represent an important class of phytohormones particularly known for their antisenescence properties that might be regulated through an effect on the oxidative metabolism. In the present work, we demonstrate the effect of CKs on catalase activity in tobacco cultivated in vitro. The catalase activity observed in suspension-cultured cells decreased slightly during the first hour of CK treatment and increased thereafter to double th e level detected in untreated cells. In contrast to these results, catalase activity was inhibited in shoot cultures in which the endogenous levels of CK were elevated by the introduction of the isopentenyltransferase gene or by an exogenous feeding of CK to the cultures. Interestingly, this catalas e inhibition correlated with an accumulation of scopolin, an inducible coum arin. Taken together, our results show that CK modulates (directly or undir ectly) catalase activity. The inverse relationship that was always found be tween scopolin accumulation and catalase activity is discussed in terms of vitrification and habituation.