HIGH-FREQUENCY PLANT-REGENERATION FROM EUCALYPTUS-GLOBULUS LABILL. HYPOCOTYLS - ONTOGENY AND PLOIDY LEVEL OF THE REGENERANTS

Up to 70% regenerating hypocotyls provided with 5 to 20 buds were obta ined on MS medium containing 0.01 or 1 mg l(-1) NAA and 0.2 mg l(-1) B A or 0.2 mg l(-1) BA and 0.2 mg l(-1) TDZ. The ability to regenerate b uds was correlated with the presence of oil glands at a stage in germi nation when oil secretion was not yet occurring. The regeneration of s hoot meristems took place from the cells involved in the differentiati on of these glands. Such glands could also appear during callus rediff erentiation, giving rise to indirect regeneration. Rooting of the rege nerants was efficient using a two-step procedure of induction under da rkness in the presence of 3 mg l(-1) IBA, followed by root development on medium devoid of growth regulators under a 16-h photoperiod, the m edium being solidified with Gelrite. Regenerated plants showed no phen otypic alterations. Nuclear DNA contents in mother-plant material and regenerants were analysed using flow cytometry. There was no evidence of polyploidy in any of the samples, indicating the absence of polyplo idisation during cell differentiation and under in vitro conditions. N o regeneration was obtained from leaf or stem explants from micropropa gated plantlets.