Changes in polyamines, auxins and peroxidase activity during in vitro rooting of Fraxinus angustifolia shoots: an auxin-independent rooting model

Among shoots of Fraxinus angustifolia Vahl raised in vitro, 76% rooted afte r culture on root induction medium for 5 days in darkness followed by cultu re on root expression medium for 15 days in light. The addition of 20.7 muM indole-butyric acid (IBA) to the root induction medium did not significant ly increase the rooting percentage (88%). Putrescine, spermidine, cyclohexy lamine (CHA) and aminoguanidine (AG) enhanced rooting up to 100% (98.66% fo r AG), when applied during root induction in the absence of IBA, otherwise these compounds inhibited rooting, as did spermine and difluoromethylornith ine (DFMO) + difluoromethylarginine (DFMA). The root induction phase was ch aracterized by a temporary increase in endogenous free indole-acetic acid ( IAA) and putrescine concentrations during root induction, whereas the root expression phase was characterized by increased peroxidase activity and low concentrations of polyamines. These changes were specifically associated w ith the rooting process and did not depend on the presence of exogenous IBA , because application of exogenous IBA enhanced the amount of IAA in the cu ttings but did not affect rooting or the pattern of changes in polyamines a nd peroxidase. The effects of CHA, AG and DFMO + DFMA on endogenous concent rations of auxins and polyamines highlight the close relationship between t he effects of IAA and putrescine in root induction and suggest that polyami ne catabolism has an important role in root formation and elongation.