The reactivation of tree peony (Paeonia suffruticosa Andr.) vitroplants by chilling is correlated with modifications of abscisic acid, auxin and cytokinin levels

In vitro rooting of Paeonia suffruticosa was correlated with an arrest of shoot development. A chilling treatment reactivated shoot development of vitroplants, and this was accompanied by an increase of mitotic activity in their apices. Chilling resulted also in the disappearance of abscisic acid from vitroshoots and the accumulation of indole-3-acetic acid in shoots and cytokinins in roots. The winter cold had a similar effect on contents of these three hormones in the mother plant in vivo; however, in contrast to the roots of the mother plant, auxin was never detected in roots of the vitroplants and cytokinin accumulation in chilled vitroshoots was almost 20-fold lower than that in buds in vivo. Despite the reactivation of vitroplants by chilling, shoots did not elongate, developed only one or two leaves and no axillary buds were formed. This limited reactivation was correlated with a rapid decrease of cytokinin and indole-3-acetic acid contents and with a new abscisic acid accumulation in vitroplants. It is considered that, during in vitro culture, explants lost their capacity to regulate hormone metabolism, and this metabolic perturbation was also maintained after transfer ex vitro.