Abstract: The aim of the research was to study the morphological and histochemical evolution of the bud meristems of 'Lavinia' nectarine cultivar. Moreover, the effectiveness of Release LC (a gibberellin chemical compound) in controlling the rate of flower bud differentiation was also evaluated. During a two-year period, the Release LC was applied in postharvest to avoid problems of possible chemical residues on marketable fruits. To determine the effect of treatment, several biological parameters such as initial flower and vegetative bud number, flower bud drop, evolution of the flower bud phenological stages, rate of bloom and fruit set were recorded. To establish the floral differentiation stage, the meristematic apices were collected before and after treatment and microscopically observed. The thin sections were analysed using histological (apex size, developmental stages of meristematic apex, co-axial stage), and histochemical (RNA fluorescent staining) techniques. In 'Lavinia' cv., the critical phase of the meristematic apex evolution occurred from May to June (60 and 90 days after full bloom): the presence of triple apices increased rapidly, the co-axial phase was achieved, the width and height of the meristematic dome increased markedly and the RNA appeared by a weak staining. As regards the flower bud differentiation control by exogenous treatments with Release LC, the different results obtained in our experiments indicate that the efficacy of treatment strictly depends on the growth stage of a meristematic apex.