Histological and Immunohistochemical Studies on Flower Induction in Olive Tree (Olea europaea L.).

Abstract The objective of this research study was to achieve additional information on the process of flower bud differentiation in two oil olive cultivars of the Tuscan’s germplasm (‘Leccino’ and ‘Puntino’). Moreover, we studied the effect of different crop load on flower bud differentiation. Samples of axillary meristematic apices were excised from the median portion of two types of one-year-old shoots: ‘ON’ (with fruits) and ‘OFF’ (without fruits). The samplings were periodically collected at different phenological stages from endocarp sclerification to early spring. The thin sections were analysed using histological (apex size), histochemical (starch, soluble carbohydrates, RNA) and immunohistochemical (ZR-Zeatin Riboside) techniques. The micromorphological observations and the histochemical procedures, used to characterise the changes in starch and total carbohydrate accumulation, didn’t permit distinguishing the apices sampled from ‘ON’ and ‘OFF’ shoots. ZR immuno-assay made it possible to identify a different localisation pattern between ‘ON’ and ‘OFF’ samples early on. The citokinine appeared distributed at dome level only in ‘OFF’ apices, particularly in July, at the endocarp sclerification phenological stage. At this time, the further strong signal observed for RNA detection could show that these changes are related to the floral evocation phase.