THE REACTIVATION OF TREE PEONY (PEONIA-SUFFRUTICOSA ANDR) VITROPLANTSBY 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 developm ent 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-ac etic acid in shoots and cytokinins in roots. The winter cold had a sim ilar effect on contents of these three hormones in the mother plant in vivo; however, in contrast to the roots of the mother plant, auxin wa s never detected in roots of the vitroplants and cytokinin accumulatio n 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 w ere formed. This limited reactivation was correlated with a rapid decr ease of cytokinin and indole-3-acetic acid contents and with a new abs cisic acid accumulation in vitroplants. It is considered that, during in vitro culture, explants lost their capacity to regulate hormone met abolism, and this metabolic perturbation was also maintained after tra nsfer ex vitro.